diff --git a/cmd/bucket-handlers.go b/cmd/bucket-handlers.go
index 23dd5b9cd..07d1a06b3 100644
--- a/cmd/bucket-handlers.go
+++ b/cmd/bucket-handlers.go
@@ -478,15 +478,11 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 	getObjectInfoFn := objectAPI.GetObjectInfo
 
 	var (
-		hasLockEnabled bool
-		dsc            ReplicateDecision
-		goi            ObjectInfo
-		gerr           error
+		dsc  ReplicateDecision
+		goi  ObjectInfo
+		gerr error
 	)
 	replicateDeletes := hasReplicationRules(ctx, bucket, deleteObjectsReq.Objects)
-	if rcfg, _ := globalBucketObjectLockSys.Get(bucket); rcfg.LockEnabled {
-		hasLockEnabled = true
-	}
 
 	type deleteResult struct {
 		delInfo DeletedObject
@@ -537,10 +533,10 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 			VersionSuspended: vc.Suspended(),
 		}
 
-		// Physical version deletes in a locked bucket are checked by the
-		// single-object path below, while its mutation lock is held. A lookup
-		// here could miss a later protection update or a protected pool copy.
-		if hasLockEnabled && object.VersionID != "" {
+		// Every physical version delete checks the version's own protection
+		// under its mutation lock. Bucket metadata may be stale or unavailable
+		// and cannot establish that a stored version is unprotected.
+		if object.VersionID != "" {
 			if first, ok := objectsToDelete[object]; ok {
 				duplicateOf[index] = first
 			} else {
@@ -605,7 +601,7 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 	bulk := make([]ObjectToDelete, 0, len(deleteList))
 	bulkIndex := make([]int, 0, len(deleteList))
 	for i, object := range deleteList {
-		if !hasLockEnabled || object.VersionID == "" {
+		if object.VersionID == "" {
 			bulk = append(bulk, object)
 			bulkIndex = append(bulkIndex, i)
 			continue
@@ -663,7 +659,7 @@ func (api objectAPIHandlers) DeleteMultipleObjectsHandler(w http.ResponseWriter,
 		// under the mutation lock, and a missing version has no stored identity.
 		dindex := objectsToDelete[deleteList[i]]
 		if errs[i] == nil || isErrObjectNotFound(errs[i]) || isErrVersionNotFound(errs[i]) {
-			if replicateDeletes && (!hasLockEnabled || deleteList[i].VersionID == "") {
+			if replicateDeletes && deleteList[i].VersionID == "" {
 				dObjects[i].ReplicationState = deleteList[i].ReplicationState()
 			}
 			deleteResults[dindex].delInfo = dObjects[i]
diff --git a/cmd/bucket-metadata-cache-security_test.go b/cmd/bucket-metadata-cache-security_test.go
new file mode 100644
index 000000000..0f511f470
--- /dev/null
+++ b/cmd/bucket-metadata-cache-security_test.go
@@ -0,0 +1,125 @@
+// Copyright (c) 2026 Feng Ruohang
+//
+// This file is part of Silo Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"context"
+	"encoding/xml"
+	"net/http"
+	"net/http/httptest"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/minio/minio/internal/auth"
+)
+
+type metadataCacheLoadBarrier struct {
+	ObjectLayer
+	key          string
+	read, resume chan struct{}
+	once         sync.Once
+}
+
+func (b *metadataCacheLoadBarrier) GetObjectNInfo(ctx context.Context, bucket, key string, rs *HTTPRangeSpec, h http.Header, opts ObjectOptions) (*GetObjectReader, error) {
+	r, err := b.ObjectLayer.GetObjectNInfo(ctx, bucket, key, rs, h, opts)
+	if bucket == minioMetaBucket && key == b.key {
+		b.once.Do(func() { close(b.read); <-b.resume })
+	}
+	return r, err
+}
+
+func TestBucketMetadataLoadPreservesConcurrentPublication(t *testing.T) {
+	defer DetectTestLeak(t)()
+	ExecObjectLayerAPITest(ExecObjectLayerAPITestArgs{
+		t: t,
+		objAPITest: func(obj ObjectLayer, backend, bucket string, _ http.Handler, _ auth.Credentials, t *testing.T) {
+			// Disk has the old unlocked config; a concurrent publication enables
+			// lock and versioning after the cache miss has started loading it.
+			enableBucketObjectLock(t, bucket)
+			newer, err := globalBucketMetadataSys.Get(bucket)
+			if err != nil {
+				t.Fatal(err)
+			}
+			globalBucketMetadataSys.Remove(bucket)
+			barrier := &metadataCacheLoadBarrier{ObjectLayer: obj, key: pathJoin(bucketMetaPrefix, bucket, bucketMetadataFile), read: make(chan struct{}), resume: make(chan struct{})}
+			previous := newObjectLayerFn()
+			setObjectLayer(barrier)
+			defer setObjectLayer(previous)
+			release := sync.OnceFunc(func() { close(barrier.resume) })
+			defer release()
+			type result struct {
+				meta     BucketMetadata
+				reloaded bool
+				err      error
+			}
+			done := make(chan result, 1)
+			go func() {
+				meta, reloaded, err := globalBucketMetadataSys.GetConfig(t.Context(), bucket)
+				done <- result{meta, reloaded, err}
+			}()
+			select {
+			case <-barrier.read:
+			case <-time.After(10 * time.Second):
+				t.Fatal("metadata load did not reach disk")
+			}
+			globalBucketMetadataSys.Set(bucket, newer)
+			release()
+			select {
+			case got := <-done:
+				if got.err != nil || got.reloaded || got.meta.objectLockConfig == nil || got.meta.objectLockConfig.ObjectLockEnabled != "Enabled" {
+					t.Fatalf("%s: stale load replaced the publication: %+v", backend, got)
+				}
+			case <-time.After(10 * time.Second):
+				t.Fatal("metadata load did not finish")
+			}
+			cached, err := globalBucketMetadataSys.Get(bucket)
+			if err != nil || cached.objectLockConfig == nil || cached.objectLockConfig.ObjectLockEnabled != "Enabled" {
+				t.Fatalf("cached lock lost: %+v %v", cached, err)
+			}
+		},
+	})
+}
+
+func TestBulkDeleteVersionLockWithStaleBucketCache(t *testing.T) {
+	for _, pools := range []int{1, 2} {
+		z, _ := bulkDeletePools(t, pools)
+		bucket, router, err := initAPIHandlerTest(t.Context(), z, nil, MakeBucketOptions{LockEnabled: true})
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, protection := range batchLockKinds {
+			oi := batchPutVersion(t, z, bucket, protection, batchLockMeta(protection))
+			saved, err := globalBucketMetadataSys.Get(bucket)
+			if err != nil {
+				t.Fatal(err)
+			}
+			globalBucketMetadataSys.Set(bucket, newBucketMetadata(bucket))
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, bulkDeleteLockRequest(t, bucket, protection, oi.VersionID))
+			globalBucketMetadataSys.Set(bucket, saved)
+			var response DeleteObjectsResponse
+			if err := xml.Unmarshal(rec.Body.Bytes(), &response); err != nil {
+				t.Fatal(err)
+			}
+			if rec.Code != http.StatusOK || len(response.Errors) != 1 || len(response.DeletedObjects) != 0 || !batchVersionExists(t, z, bucket, protection, oi.VersionID) {
+				t.Fatalf("pools=%d %s: stale bucket cache bypassed version lock: %s", pools, protection, rec.Body.String())
+			}
+		}
+	}
+}
diff --git a/cmd/bucket-metadata-sys.go b/cmd/bucket-metadata-sys.go
index afe09e6aa..2ca8dab0f 100644
--- a/cmd/bucket-metadata-sys.go
+++ b/cmd/bucket-metadata-sys.go
@@ -697,7 +697,7 @@ func (sys *BucketMetadataSys) GetConfig(ctx context.Context, bucket string) (met
 	}
 
 	val, err, _ := sys.group.Do(bucket, func() (val any, err error) {
-		meta, err = loadBucketMetadata(ctx, objAPI, bucket)
+		meta, err := loadBucketMetadata(ctx, objAPI, bucket)
 		if err != nil {
 			if !sys.Initialized() {
 				// bucket metadata not yet initialized
@@ -707,13 +707,18 @@ func (sys *BucketMetadataSys) GetConfig(ctx context.Context, bucket string) (met
 		return meta, err
 	})
 	meta, _ = val.(BucketMetadata)
+	sys.Lock()
+	defer sys.Unlock()
+	// A writer may have published a newer configuration while the disk read
+	// was in flight. Never replace that publication with the older load.
+	if current, ok := sys.metadataMap[bucket]; ok {
+		return current, false, nil
+	}
 	if err != nil {
 		return meta, false, err
 	}
-	sys.Lock()
 	sys.metadataMap[bucket] = meta
 	sys.clearLoadFailure(bucket)
-	sys.Unlock()
 
 	return meta, true, nil
 }
diff --git a/cmd/bucket-object-lock.go b/cmd/bucket-object-lock.go
index f791d7a12..25fdcaa1e 100644
--- a/cmd/bucket-object-lock.go
+++ b/cmd/bucket-object-lock.go
@@ -491,6 +491,25 @@ func (s objectLockState) legalHoldIsOlderThan(src time.Time) bool {
 	return olderThan(s.legalHoldTimestamp, src)
 }
 
+// A peer's ordering timestamp cannot override an unexpired COMPLIANCE lock.
+// Otherwise it could first remove retention with a same-content retransmit,
+// then replace the now-unprotected version in a second request.
+func (s objectLockState) complianceWouldWeaken(incoming objectLockState) bool {
+	if s.mode != string(objectlock.RetCompliance) {
+		return false
+	}
+	until, err := time.Parse(time.RFC3339Nano, s.retainUntil)
+	if err != nil {
+		return true
+	}
+	now, err := objectlock.UTCNowNTP()
+	if err == nil && !until.After(now) {
+		return false
+	}
+	nextUntil, nextErr := time.Parse(time.RFC3339Nano, incoming.retainUntil)
+	return incoming.mode != string(objectlock.RetCompliance) || nextErr != nil || nextUntil.Before(until)
+}
+
 // restoreRetention and restoreLegalHold put the stored state back into
 // metadata that was rebuilt from a request whose update was not applied.
 func (s objectLockState) restoreRetention(metadata map[string]string) {
@@ -610,7 +629,7 @@ func reconcileStoredObjectLock(metadata map[string]string, stored objectLockStat
 	incoming := storedObjectLockState(metadata)
 
 	incomingRetentionTS, _ := time.Parse(time.RFC3339Nano, incoming.retentionTimestamp)
-	if !stored.retentionIsOlderThan(incomingRetentionTS) {
+	if !stored.retentionIsOlderThan(incomingRetentionTS) || stored.complianceWouldWeaken(incoming) {
 		// The stored retention is at least as new as the incoming one (or the
 		// incoming update is unordered): drop the incoming value and put the stored
 		// state back, which may itself be a removal (value keys absent, timestamp
diff --git a/cmd/erasure-multipart.go b/cmd/erasure-multipart.go
index 12b662fe5..5049b1320 100644
--- a/cmd/erasure-multipart.go
+++ b/cmd/erasure-multipart.go
@@ -1722,6 +1722,9 @@ func (er erasureObjects) CompleteMultipartUpload(ctx context.Context, bucket str
 		}
 	}
 
+	if err := er.checkReplicaContent(ctx, bucket, object, minioMetaMultipartBucket, uploadIDPath, partsMetadata, onlineDisks, opts); err != nil {
+		return oi, toObjectErr(err, bucket, object)
+	}
 	er.cleanupMultipartPath(ctx, paths...) // cleanup all part.N.meta, and skipped part.N's before final rename().
 
 	defer func() {
diff --git a/cmd/erasure-object.go b/cmd/erasure-object.go
index 61a31aa15..fec815c73 100644
--- a/cmd/erasure-object.go
+++ b/cmd/erasure-object.go
@@ -148,6 +148,17 @@ func (er erasureObjects) CopyObject(ctx context.Context, srcBucket, srcObject, d
 			fi.IsLatest = true // we are creating a new version so this is latest.
 		}
 	}
+	if srcInfo.versionOnly && (dstOpts.ReplicaLockReconcile || dstOpts.ReplicationRequest) && !dstOpts.DataMovement {
+		candidate := slices.Clone(metaArr)
+		for i := range candidate {
+			candidate[i].VersionID = versionID
+			candidate[i].Metadata = srcInfo.UserDefined
+		}
+		readDisks, readMeta := shuffleDisksAndPartsMetadataByIndex(onlineDisks, candidate, fi)
+		if err := er.checkReplicaContent(ctx, dstBucket, dstObject, srcBucket, srcObject, readMeta, readDisks, dstOpts); err != nil {
+			return oi, err
+		}
+	}
 
 	if !dstOpts.ReplicationRequest && !dstOpts.ReplicaLockReconcile && !dstOpts.DataMovement &&
 		(versionID == "" || versionID == nullVersionID) {
@@ -1722,6 +1733,9 @@ func (er erasureObjects) putObject(ctx context.Context, bucket string, object st
 	}
 
 	// Rename the successfully written temporary object to final location.
+	if err := er.checkReplicaContent(ctx, bucket, object, minioMetaTmpBucket, tempObj, partsMetadata, onlineDisks, opts); err != nil {
+		return ObjectInfo{}, toObjectErr(err, bucket, object)
+	}
 	onlineDisks, versions, oldDataDir, err := renameData(ctx, onlineDisks, minioMetaTmpBucket, tempObj, partsMetadata, bucket, object, writeQuorum)
 	if err != nil {
 		if errors.Is(err, errFileNotFound) {
diff --git a/cmd/erasure-server-pool-put-conditional_test.go b/cmd/erasure-server-pool-put-conditional_test.go
index cd4897921..cef91faa2 100644
--- a/cmd/erasure-server-pool-put-conditional_test.go
+++ b/cmd/erasure-server-pool-put-conditional_test.go
@@ -590,9 +590,9 @@ func TestSinglePoolConditionalPutHTTP(t *testing.T) {
 	}
 }
 
-// An internal replica callback without an addressed version is not a public
-// condition. Preserve its availability when another pool is unreadable. An
-// addressed replica already requires all pools for lock/tag reconciliation.
+// Replica overwrites must establish protection across every pool, including
+// the null version of an unversioned request. An unreadable pool may hold a
+// protected copy, so neither addressed nor unaddressed writes may replace it.
 func TestPoolsConditionalPutReplicaAvailability(t *testing.T) {
 	for _, addressed := range []bool{false, true} {
 		t.Run(fmt.Sprintf("addressed=%t", addressed), func(t *testing.T) {
@@ -615,10 +615,9 @@ func TestPoolsConditionalPutReplicaAvailability(t *testing.T) {
 				xhttp.MinIOSourceETag:               fmt.Sprintf("%x", md5.Sum([]byte("replacement"))),
 			}
 			url := getPutObjectURL("", bucket, object)
-			wantStatus, wantBody := http.StatusOK, "replacement"
+			wantStatus, wantBody := http.StatusServiceUnavailable, "old"
 			if addressed {
 				url += "?versionId=" + oi.VersionID
-				wantStatus, wantBody = http.StatusServiceUnavailable, "old"
 			}
 			put := multipartConditionRequest(t, router, http.MethodPut, url, "replacement", headers)
 			if put.Code != wantStatus {
diff --git a/cmd/erasure-server-pool.go b/cmd/erasure-server-pool.go
index 907a88b18..6a9dbdd6e 100644
--- a/cmd/erasure-server-pool.go
+++ b/cmd/erasure-server-pool.go
@@ -1195,6 +1195,7 @@ func (z *erasureServerPools) PutObject(ctx context.Context, bucket string, objec
 	if opts.replicaObjectInfo == nil && (opts.ReplicaLockReconcile || !opts.ReplicationRequest) {
 		opts.replicaObjectInfo = z.replicaObjectInfo
 	}
+	opts.replicaContentGuard = z.guardReplicaContent
 	oi, err := z.serverPools[idx].PutObject(ctx, bucket, object, data, opts)
 	if err == nil && opts.ReplicaLockReconcile && !opts.DataMovement {
 		err = z.retireReplicaCopies(ctx, bucket, object, idx, oi)
@@ -1749,6 +1750,9 @@ func (z *erasureServerPools) CopyObject(ctx context.Context, srcBucket, srcObjec
 		return objInfo, err
 	}
 
+	if !z.SinglePool() {
+		dstOpts.replicaContentGuard = z.guardReplicaContent
+	}
 	if !z.SinglePool() && (dstOpts.ReplicaLockReconcile || !dstOpts.ReplicationRequest) {
 		dstOpts.replicaObjectInfo = z.replicaObjectInfo
 		if dstOpts.ReplicaLockReconcile && !dstOpts.DataMovement {
@@ -1799,6 +1803,7 @@ func (z *erasureServerPools) CopyObject(ctx context.Context, srcBucket, srcObjec
 		ReplicaLockReconcile:       dstOpts.ReplicaLockReconcile,
 		DataMovement:               dstOpts.DataMovement,
 		replicaObjectInfo:          dstOpts.replicaObjectInfo,
+		replicaContentGuard:        dstOpts.replicaContentGuard,
 	}
 
 	return z.serverPools[poolIdx].PutObject(ctx, dstBucket, dstObject, srcInfo.PutObjReader, putOpts)
@@ -2524,6 +2529,7 @@ func (z *erasureServerPools) CompleteMultipartUpload(ctx context.Context, bucket
 		opts.replicaObjectInfo = z.replicaObjectInfo
 	}
 
+	opts.replicaContentGuard = z.guardReplicaContent
 	for idx, pool := range z.serverPools {
 		if z.IsSuspended(idx) {
 			continue
diff --git a/cmd/object-api-interface.go b/cmd/object-api-interface.go
index 2ad350169..ffd21230d 100644
--- a/cmd/object-api-interface.go
+++ b/cmd/object-api-interface.go
@@ -122,6 +122,8 @@ type ObjectOptions struct {
 
 	// Pools-layer version resolver; the caller holds the shared object lock.
 	replicaObjectInfo GetObjectInfoFn
+	// Verifies protected content in every pool before a replica commits.
+	replicaContentGuard replicaContentGuardFn
 
 	// RefuseLockedOverwrite refuses, under the destination's write lock, a
 	// write that would replace a stored version Object Lock protects: the
diff --git a/cmd/replica-content.go b/cmd/replica-content.go
new file mode 100644
index 000000000..542130c14
--- /dev/null
+++ b/cmd/replica-content.go
@@ -0,0 +1,205 @@
+// Copyright (c) 2026 Feng Ruohang
+//
+// This file is part of Silo Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"net/http"
+
+	"github.com/minio/minio/internal/crypto"
+	"github.com/minio/minio/internal/hash/sha256"
+	xioutil "github.com/minio/minio/internal/ioutil"
+)
+
+type replicaContentGuardFn func(context.Context, string, string, ObjectInfo, func() (*GetObjectReader, error)) error
+
+// verifyLockedReplica compares the actual data, never a sender's ETag or
+// checksum assertion. A peer may retransmit a protected version to update its
+// metadata, but may not replace its content. Call under the object write lock.
+func verifyLockedReplica(ctx context.Context, incoming, stored ObjectInfo, openIncoming, openStored func() (*GetObjectReader, error)) error {
+	if !enforceRetentionForDeletion(ctx, stored) {
+		return nil
+	}
+	locked := ObjectLocked{Bucket: stored.Bucket, Object: stored.Name, VersionID: stored.VersionID}
+	if storedObjectLockState(stored.UserDefined).complianceWouldWeaken(storedObjectLockState(incoming.UserDefined)) {
+		return locked
+	}
+	inSSEC, oldSSEC := crypto.SSEC.IsEncrypted(incoming.UserDefined), crypto.SSEC.IsEncrypted(stored.UserDefined)
+	if inSSEC != oldSSEC {
+		return locked
+	}
+	if inSSEC {
+		inSize, inErr := incoming.GetActualSize()
+		oldSize, oldErr := stored.GetActualSize()
+		if inErr != nil || oldErr != nil || inSize != oldSize {
+			return locked
+		}
+		// Without the customer key, compare ciphertext and its interpretation.
+		// Equal ciphertext with a changed seal or multipart framing is not the
+		// same object, even if the supplied ETag and size are unchanged.
+		for _, key := range []string{
+			crypto.MetaIV, crypto.MetaAlgorithm, crypto.MetaSealedKeySSEC,
+			ReservedMetadataPrefix + "compression",
+		} {
+			if incoming.UserDefined[key] != stored.UserDefined[key] {
+				return locked
+			}
+		}
+		if crypto.IsMultiPart(incoming.UserDefined) != crypto.IsMultiPart(stored.UserDefined) || incoming.isMultipart() != stored.isMultipart() {
+			return locked
+		}
+		if crypto.IsMultiPart(incoming.UserDefined) {
+			if len(incoming.Parts) != len(stored.Parts) {
+				return locked
+			}
+			for i, p := range incoming.Parts {
+				old := stored.Parts[i]
+				if p.Number != old.Number || p.Size != old.Size {
+					return locked
+				}
+			}
+		}
+	}
+	in, err := openIncoming()
+	if err != nil {
+		return err
+	}
+	defer in.Close()
+	old, err := openStored()
+	if err != nil {
+		return err
+	}
+	defer old.Close()
+	ih, oh := sha256.New(), sha256.New()
+	inSize, err := io.Copy(ih, in)
+	if err != nil {
+		return err
+	}
+	oldSize, err := io.Copy(oh, old)
+	if err != nil {
+		return err
+	}
+	if inSize != oldSize || !bytes.Equal(ih.Sum(nil), oh.Sum(nil)) {
+		return locked
+	}
+	return nil
+}
+
+func (er erasureObjects) guardReplicaContent(ctx context.Context, bucket, object string, incoming ObjectInfo, openIncoming func() (*GetObjectReader, error)) error {
+	opts := ObjectOptions{VersionID: incoming.VersionID, NoLock: true, NoAuditLog: true, ReplicationRequest: true}
+	if opts.VersionID == "" {
+		opts.VersionID = nullVersionID
+	}
+	stored, err := er.getObjectInfo(ctx, bucket, object, opts)
+	if isErrObjectNotFound(err) || isErrVersionNotFound(err) || isErrMethodNotAllowed(err) {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	return verifyLockedReplica(ctx, incoming, stored, openIncoming, func() (*GetObjectReader, error) {
+		return er.GetObjectNInfo(ctx, bucket, object, nil, http.Header{}, opts)
+	})
+}
+
+func (z *erasureServerPools) guardReplicaContent(ctx context.Context, bucket, object string, incoming ObjectInfo, openIncoming func() (*GetObjectReader, error)) error {
+	opts := ObjectOptions{VersionID: incoming.VersionID, NoLock: true, NoAuditLog: true, ReplicationRequest: true}
+	if opts.VersionID == "" {
+		opts.VersionID = nullVersionID
+	}
+	copies, err := z.objectPoolInfos(ctx, bucket, object, opts)
+	if isErrObjectNotFound(err) || isErrVersionNotFound(err) {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+	for _, copy := range copies {
+		if err := verifyLockedReplica(ctx, incoming, copy.ObjInfo, openIncoming, func() (*GetObjectReader, error) {
+			return z.serverPools[copy.Index].GetObjectNInfo(ctx, bucket, object, nil, http.Header{}, opts)
+		}); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// checkReplicaContent reads the staged version before rename commits it. Its
+// data is decoded/decrypted just like a GET (raw ciphertext for SSE-C), so this
+// covers multipart, compression and destination SSE-S3/KMS re-encryption.
+// disks and metadata are in erasure shard order, as passed to renameData.
+func (er erasureObjects) checkReplicaContent(ctx context.Context, bucket, object, stageBucket, stageObject string, metadata []FileInfo, disks []StorageAPI, opts ObjectOptions) error {
+	if (!opts.ReplicaLockReconcile && !opts.ReplicationRequest) || opts.DataMovement {
+		return nil
+	}
+	var fi FileInfo
+	for i, disk := range disks {
+		if disk != nil {
+			fi = metadata[i]
+			break
+		}
+	}
+	incoming := fi.ToObjectInfo(bucket, object, opts.Versioned || opts.VersionSuspended)
+	guard := opts.replicaContentGuard
+	if guard == nil {
+		guard = er.guardReplicaContent
+	}
+	return guard(ctx, bucket, object, incoming, func() (*GetObjectReader, error) {
+		// A marker-only peer write does not reconcile the stored protection.
+		// It therefore cannot replace a protected version, even with equal data.
+		if !opts.ReplicaLockReconcile {
+			return nil, ObjectLocked{Bucket: bucket, Object: decodeDirObject(object), VersionID: incoming.VersionID}
+		}
+		if incoming.IsCompressed() {
+			// A replica may assert the source's logical size. A compressed GET
+			// limits its output to that size, so verify it against the lengths
+			// recorded while consuming the uploaded parts before comparing GETs.
+			// Otherwise a forged zero size could hide a non-empty replacement.
+			var actual int64
+			for _, part := range incoming.Parts {
+				actual += part.ActualSize
+			}
+			declared, err := incoming.GetActualSize()
+			if err != nil || declared != actual {
+				return nil, ObjectLocked{Bucket: bucket, Object: decodeDirObject(object), VersionID: incoming.VersionID}
+			}
+		}
+		readOpts := ObjectOptions{NoDecryption: crypto.SSEC.IsEncrypted(incoming.UserDefined)}
+		fn, off, length, err := NewGetObjectReader(nil, incoming, readOpts, http.Header{})
+		if err != nil {
+			return nil, err
+		}
+		// The ordinary reader expects original drive order, not shard order.
+		readDisks, readMeta := make([]StorageAPI, len(disks)), make([]FileInfo, len(metadata))
+		for i, shard := range fi.Erasure.Distribution {
+			readDisks[i], readMeta[i] = disks[shard-1], metadata[shard-1]
+			readMeta[i].Erasure.Index = shard
+		}
+		pr, pw := xioutil.WaitPipe()
+		go func() {
+			pw.CloseWithError(er.getObjectWithFileInfo(ctx, stageBucket, stageObject, off, length, pw, fi, readMeta, readDisks))
+		}()
+		reader, err := fn(pr, http.Header{}, func() { pr.CloseWithError(nil) })
+		if err != nil {
+			pr.CloseWithError(err)
+		}
+		return reader, err
+	})
+}
diff --git a/cmd/replica-content_test.go b/cmd/replica-content_test.go
new file mode 100644
index 000000000..5291f4b1e
--- /dev/null
+++ b/cmd/replica-content_test.go
@@ -0,0 +1,314 @@
+// Copyright (c) 2026 Feng Ruohang
+//
+// This file is part of Silo Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"bytes"
+	"encoding/xml"
+	"fmt"
+	"io"
+	"maps"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/minio/minio/internal/auth"
+	"github.com/minio/minio/internal/crypto"
+	xhttp "github.com/minio/minio/internal/http"
+	"github.com/minio/minio/internal/kms"
+)
+
+func TestAPIReplicaPreservesProtectedContent(t *testing.T) {
+	defer DetectTestLeak(t)()
+	ExecObjectLayerAPITest(ExecObjectLayerAPITestArgs{
+		t: t, makeBucketOptions: MakeBucketOptions{LockEnabled: true},
+		objAPITest: func(obj ObjectLayer, backend, bucket string, router http.Handler, cred auth.Credentials, t *testing.T) {
+			oldTLS, oldKMS := globalIsTLS, GlobalKMS
+			globalIsTLS, GlobalKMS = true, kms.NewStub("replica-content")
+			defer func() { globalIsTLS, GlobalKMS = oldTLS, oldKMS }()
+			restoreCompression := disableCompression()
+			defer restoreCompression()
+			request := func(method, url string, data []byte, headers map[string]string) *httptest.ResponseRecorder {
+				t.Helper()
+				req, err := newTestSignedRequestV4(method, url, int64(len(data)), bytes.NewReader(data), cred.AccessKey, cred.SecretKey, headers)
+				if err != nil {
+					t.Fatal(err)
+				}
+				rec := httptest.NewRecorder()
+				router.ServeHTTP(rec, req)
+				return rec
+			}
+			for _, encryption := range []string{"plain", "sse-s3", "sse-kms", "sse-c", "plain-compressed", "sse-s3-compressed"} {
+				restore := func() {}
+				if strings.HasSuffix(encryption, "-compressed") {
+					restore = setCopyChecksumCompression(true)
+				}
+				for _, multipart := range []bool{false, true} {
+					for _, protection := range []string{"COMPLIANCE", "LEGALHOLD", "GOVERNANCE"} {
+						key := fmt.Sprintf("protected/%s/%v/%s.txt", encryption, multipart, protection)
+						enc := map[string]string{}
+						switch encryption {
+						case "sse-s3", "sse-s3-compressed":
+							enc[xhttp.AmzServerSideEncryption] = xhttp.AmzEncryptionAES
+						case "sse-kms":
+							enc[xhttp.AmzServerSideEncryption] = xhttp.AmzEncryptionKMS
+							enc[xhttp.AmzServerSideEncryptionKmsID] = "replica-content"
+						case "sse-c":
+							enc = ssecKeyHeaders(bytes.Repeat([]byte{0x37}, 32), false)
+						}
+						headers := maps.Clone(enc)
+						maps.Copy(headers, batchLockMeta(protection))
+						// Both inline and disk-backed writes are exercised.
+						body := bytes.Repeat([]byte("immutable content "), 20000)
+						switch protection {
+						case "LEGALHOLD":
+							body = body[:64]
+						case "GOVERNANCE":
+							body = nil
+						}
+						if !multipart {
+							putCopyChecksumSource(t, router, cred, bucket, key, body, headers)
+						} else {
+							initRec := request(http.MethodPost, getNewMultipartURL("", bucket, key), nil, headers)
+							if initRec.Code != http.StatusOK {
+								t.Fatalf("source initiate: %d %s", initRec.Code, initRec.Body.String())
+							}
+							var init InitiateMultipartUploadResponse
+							if err := xml.Unmarshal(initRec.Body.Bytes(), &init); err != nil {
+								t.Fatal(err)
+							}
+							part := request(http.MethodPut, getPutObjectPartURL("", bucket, key, init.UploadID, "1"), body, enc)
+							if part.Code != http.StatusOK {
+								t.Fatalf("source part: %d %s", part.Code, part.Body.String())
+							}
+							complete, err := xml.Marshal(CompleteMultipartUpload{Parts: []CompletePart{{PartNumber: 1, ETag: canonicalizeETag(part.Header()[xhttp.ETag][0])}}})
+							if err != nil {
+								t.Fatal(err)
+							}
+							rec := request(http.MethodPost, getCompleteMultipartUploadURL("", bucket, key, init.UploadID), complete, enc)
+							if rec.Code != http.StatusOK {
+								t.Fatalf("source complete: %d %s", rec.Code, rec.Body.String())
+							}
+						}
+						gr, err := obj.GetObjectNInfo(t.Context(), bucket, key, nil, http.Header{}, ObjectOptions{ReplicationRequest: true})
+						if err != nil {
+							t.Fatal(err)
+						}
+						src := gr.ObjInfo
+						wire, err := io.ReadAll(gr)
+						gr.Close()
+						if err != nil {
+							t.Fatal(err)
+						}
+						for _, altered := range []bool{true, false} {
+							data := bytes.Clone(wire)
+							if altered {
+								if len(data) == 0 {
+									data = []byte("x")
+								} else {
+									data[len(data)-1] ^= 0x20
+								}
+							}
+							opts, _, err := putReplicationOpts(t.Context(), "", src)
+							if err != nil {
+								t.Fatal(err)
+							}
+							hdrs := map[string]string{}
+							for k, vs := range opts.Header() {
+								if len(vs) > 0 {
+									hdrs[k] = vs[0]
+								}
+							}
+							hdrs[xhttp.MinIOSourceReplicationRequest] = "true"
+							hdrs[xhttp.AmzBucketReplicationStatus] = "REPLICA"
+							// Forge the old ETag and size along with a newer tag revision:
+							// the body comparison must still reject different bytes.
+							hdrs[xhttp.MinIOSourceETag] = src.ETag
+							hdrs[xhttp.MinIOSourceTaggingTimestamp] = UTCNow().Add(time.Minute).Format(time.RFC3339Nano)
+							hdrs[xhttp.AmzObjectTagging] = "replica=updated"
+							var rec *httptest.ResponseRecorder
+							if !multipart {
+								rec = request(http.MethodPut, getPutObjectURL("", bucket, key)+"?versionId="+src.VersionID, data, hdrs)
+							} else {
+								initRec := request(http.MethodPost, getNewMultipartURL("", bucket, key)+"&versionId="+src.VersionID, nil, hdrs)
+								if initRec.Code != http.StatusOK {
+									t.Fatalf("%s %s initiate: %d %s", backend, key, initRec.Code, initRec.Body.String())
+								}
+								var init InitiateMultipartUploadResponse
+								if err := xml.Unmarshal(initRec.Body.Bytes(), &init); err != nil {
+									t.Fatal(err)
+								}
+								partHdrs := map[string]string{xhttp.MinIOSourceReplicationRequest: "true"}
+								partRec := request(http.MethodPut, getPutObjectPartURL("", bucket, key, init.UploadID, "1"), data, partHdrs)
+								if partRec.Code != http.StatusOK && (!altered || !strings.Contains(partRec.Body.String(), "XMinioObjectTampered")) {
+									t.Fatalf("%s %s part: %d %s", backend, key, partRec.Code, partRec.Body.String())
+								}
+								if partRec.Code != http.StatusOK {
+									rec = partRec
+								} else {
+									complete, err := xml.Marshal(CompleteMultipartUpload{Parts: []CompletePart{{PartNumber: 1, ETag: canonicalizeETag(partRec.Header()[xhttp.ETag][0])}}})
+									if err != nil {
+										t.Fatal(err)
+									}
+									actual, err := src.GetActualSize()
+									if err != nil {
+										t.Fatal(err)
+									}
+									partHdrs[xhttp.MinIOReplicationActualObjectSize] = strconv.FormatInt(actual, 10)
+									rec = request(http.MethodPost, getCompleteMultipartUploadURL("", bucket, key, init.UploadID), complete, partHdrs)
+								}
+							}
+							if altered {
+								if rec.Code < 400 || !strings.Contains(rec.Body.String(), "WORM") && !strings.Contains(rec.Body.String(), "XMinioObjectTampered") {
+									t.Fatalf("%s %s: different content not refused: %d %s", backend, key, rec.Code, rec.Body.String())
+								}
+							} else if rec.Code != http.StatusOK {
+								t.Fatalf("%s %s: same content refused: %d %s", backend, key, rec.Code, rec.Body.String())
+							}
+							getHdrs := map[string]string{}
+							if encryption == "sse-c" {
+								getHdrs = enc
+							}
+							got := request(http.MethodGet, getGetObjectURL("", bucket, key)+"?versionId="+src.VersionID, nil, getHdrs)
+							if got.Code != http.StatusOK || !bytes.Equal(got.Body.Bytes(), body) {
+								t.Fatalf("%s %s: protected content changed or became unreadable: %d", backend, key, got.Code)
+							}
+						}
+					}
+				}
+				restore()
+			}
+		},
+	})
+}
+
+func TestPoolsReplicaProtectedContentAcrossPools(t *testing.T) {
+	z, bucket := consistencyPools(t)
+	const key = "protected-across-pools"
+	id := mustGetUUID()
+	stamp := UTCNow().Add(-time.Hour)
+	putConsistencyObject(t, z, bucket, key, 0, "original", ObjectOptions{Versioned: true, VersionID: id, MTime: stamp})
+	putConsistencyObject(t, z, bucket, key, 1, "original", ObjectOptions{Versioned: true, VersionID: id, MTime: stamp, UserDefined: batchLockMeta("COMPLIANCE")})
+	_, err := z.PutObject(t.Context(), bucket, key, mustGetPutObjReader(t, strings.NewReader("tampered"), 8, "", ""), ObjectOptions{Versioned: true, VersionID: id, ReplicationRequest: true, ReplicaLockReconcile: true, UserDefined: map[string]string{}})
+	if _, ok := err.(ObjectLocked); !ok {
+		t.Fatalf("protected pool copy allowed overwrite: %v", err)
+	}
+	for i, pool := range z.serverPools {
+		gr, err := pool.GetObjectNInfo(t.Context(), bucket, key, nil, http.Header{}, ObjectOptions{VersionID: id})
+		if err != nil {
+			t.Fatal(err)
+		}
+		data, err := io.ReadAll(gr)
+		gr.Close()
+		if err != nil || string(data) != "original" {
+			t.Fatalf("pool %d: changed protected data: %q %v", i, data, err)
+		}
+	}
+}
+
+func TestLockedSSECReplicaRejectsChangedSeal(t *testing.T) {
+	stored := ObjectInfo{Bucket: "bucket", Name: "key", Size: 0, UserDefined: batchLockMeta("LEGALHOLD")}
+	stored.UserDefined[crypto.MetaSealedKeySSEC] = "stored-seal"
+	incoming := stored
+	incoming.UserDefined = maps.Clone(stored.UserDefined)
+	incoming.UserDefined[crypto.MetaSealedKeySSEC] = "changed-seal"
+	open := func() (*GetObjectReader, error) {
+		t.Fatal("changed seal must be rejected before reading")
+		return nil, nil
+	}
+	if err := verifyLockedReplica(t.Context(), incoming, stored, open, open); err == nil {
+		t.Fatal("changed SSE-C seal accepted")
+	}
+}
+
+func TestAPIReplicaCopyPreservesProtectedVersion(t *testing.T) {
+	defer DetectTestLeak(t)()
+	ExecObjectLayerAPITest(ExecObjectLayerAPITestArgs{
+		t: t, makeBucketOptions: MakeBucketOptions{LockEnabled: true},
+		objAPITest: func(obj ObjectLayer, backend, bucket string, router http.Handler, cred auth.Credentials, t *testing.T) {
+			const key = "copy-protected-version"
+			original := batchPutVersion(t, obj, bucket, key, batchLockMeta("COMPLIANCE"))
+			data := []byte("different source version")
+			source, err := obj.PutObject(t.Context(), bucket, key, mustGetPutObjReader(t, bytes.NewReader(data), int64(len(data)), "", ""), ObjectOptions{Versioned: true})
+			if err != nil {
+				t.Fatal(err)
+			}
+			headers := map[string]string{
+				xhttp.AmzCopySource:                 url.QueryEscape("/"+bucket+"/"+key) + "?versionId=" + source.VersionID,
+				xhttp.MinIOSourceReplicationRequest: "true", xhttp.AmzBucketReplicationStatus: "REPLICA",
+				xhttp.AmzMetadataDirective: replaceDirective,
+			}
+			req, err := newTestSignedRequestV4(http.MethodPut, getCopyObjectURL("", bucket, key)+"?versionId="+original.VersionID, 0, nil, cred.AccessKey, cred.SecretKey, headers)
+			if err != nil {
+				t.Fatal(err)
+			}
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, req)
+			if rec.Code < 400 || !strings.Contains(rec.Body.String(), "WORM") {
+				t.Fatalf("%s: copy replaced protected version: %d %s", backend, rec.Code, rec.Body.String())
+			}
+			gr, err := obj.GetObjectNInfo(t.Context(), bucket, key, nil, http.Header{}, ObjectOptions{VersionID: original.VersionID})
+			if err != nil {
+				t.Fatal(err)
+			}
+			got, err := io.ReadAll(gr)
+			gr.Close()
+			if err != nil || string(got) != "batch lock "+key {
+				t.Fatalf("%s: protected body changed: %q %v", backend, got, err)
+			}
+		},
+	})
+}
+
+func TestAPIReplicaCannotWeakenCompliance(t *testing.T) {
+	defer DetectTestLeak(t)()
+	ExecObjectLayerAPITest(ExecObjectLayerAPITestArgs{
+		t: t, makeBucketOptions: MakeBucketOptions{LockEnabled: true},
+		objAPITest: func(obj ObjectLayer, backend, bucket string, router http.Handler, cred auth.Credentials, t *testing.T) {
+			const key = "compliance-removal"
+			oi := batchPutVersion(t, obj, bucket, key, batchLockMeta("COMPLIANCE"))
+			until := oi.UserDefined[strings.ToLower(xhttp.AmzObjectLockRetainUntilDate)]
+			for _, copyRequest := range []bool{false, true} {
+				headers := map[string]string{xhttp.MinIOSourceReplicationRequest: "true", xhttp.AmzBucketReplicationStatus: "REPLICA", xhttp.MinIOSourceObjectRetentionTimestamp: UTCNow().Add(time.Hour).Format(time.RFC3339Nano)}
+				body := []byte("batch lock " + key)
+				if copyRequest {
+					headers[xhttp.AmzCopySource] = url.QueryEscape("/"+bucket+"/"+key) + "?versionId=" + oi.VersionID
+					headers[xhttp.AmzMetadataDirective] = replaceDirective
+					body = nil
+				}
+				req, err := newTestSignedRequestV4(http.MethodPut, getPutObjectURL("", bucket, key)+"?versionId="+oi.VersionID, int64(len(body)), bytes.NewReader(body), cred.AccessKey, cred.SecretKey, headers)
+				if err != nil {
+					t.Fatal(err)
+				}
+				rec := httptest.NewRecorder()
+				router.ServeHTTP(rec, req)
+				if rec.Code != http.StatusOK {
+					t.Fatalf("%s copy=%v: %d %s", backend, copyRequest, rec.Code, rec.Body.String())
+				}
+				stored, err := obj.GetObjectInfo(t.Context(), bucket, key, ObjectOptions{VersionID: oi.VersionID})
+				if err != nil || stored.UserDefined[strings.ToLower(xhttp.AmzObjectLockMode)] != "COMPLIANCE" || stored.UserDefined[strings.ToLower(xhttp.AmzObjectLockRetainUntilDate)] != until {
+					t.Fatalf("%s copy=%v: a replica cleared COMPLIANCE: %+v %v", backend, copyRequest, stored.UserDefined, err)
+				}
+			}
+		},
+	})
+}
diff --git a/cmd/replication-signed-headers_test.go b/cmd/replication-signed-headers_test.go
new file mode 100644
index 000000000..7e02a6e13
--- /dev/null
+++ b/cmd/replication-signed-headers_test.go
@@ -0,0 +1,94 @@
+// Copyright (c) 2026 Feng Ruohang
+//
+// This file is part of Silo Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"bytes"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/minio/minio/internal/auth"
+	xhttp "github.com/minio/minio/internal/http"
+)
+
+func TestReplicationControlsRequireSignedHeaders(t *testing.T) {
+	for _, header := range replicationRequestHeaders {
+		t.Run(header, func(t *testing.T) {
+			req, err := newTestSignedRequestV4(http.MethodGet, "http://localhost/bucket/key", 0, nil, "access-key", "secret-key", nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			// Membership matters even for a present-empty internal header.
+			req.Header.Set(header, "")
+			if replicationHeadersSigned(req) {
+				t.Fatal("unsigned control granted replication trust")
+			}
+			if err := signRequestV4(req, "access-key", "secret-key"); err != nil {
+				t.Fatal(err)
+			}
+			if !replicationHeadersSigned(req) {
+				t.Fatal("signed control rejected")
+			}
+		})
+	}
+	for _, authorization := range []string{"", "AWS access-key:signature", "Credential=access-key"} {
+		req := httptest.NewRequest(http.MethodGet, "/bucket/key", nil)
+		req.Header.Set(xhttp.Authorization, authorization)
+		req.Header.Set(xhttp.MinIOSourceReplicationRequest, "true")
+		if replicationHeadersSigned(req) {
+			t.Fatalf("non-SigV4 authorization granted trust: %q", authorization)
+		}
+	}
+	req := httptest.NewRequest(http.MethodGet, "http://localhost/bucket/key", nil)
+	req.Header.Set(xhttp.MinIOSourceReplicationRequest, "true")
+	presignBoundaryRequest(t, req, UTCNow(), []string{"host", "x-minio-source-replication-request"}, auth.Credentials{AccessKey: "access-key", SecretKey: "secret-key"})
+	getRequestAuthType(req)
+	if replicationHeadersSigned(req) {
+		t.Fatal("presigned request granted peer trust")
+	}
+}
+
+func TestAPIUnsignedReplicationControlsAreIgnored(t *testing.T) {
+	defer DetectTestLeak(t)()
+	ExecObjectLayerAPITest(ExecObjectLayerAPITestArgs{
+		t: t, endpoints: []string{"PutObject"},
+		objAPITest: func(obj ObjectLayer, backend, bucket string, router http.Handler, cred auth.Credentials, t *testing.T) {
+			for _, signedMarker := range []bool{false, true} {
+				headers := map[string]string{}
+				if signedMarker {
+					headers[xhttp.MinIOSourceReplicationRequest] = "true"
+				}
+				body := []byte("replication controls are authenticated")
+				req, err := newTestSignedRequestV4(http.MethodPut, getPutObjectURL("", bucket, "key"), int64(len(body)), bytes.NewReader(body), cred.AccessKey, cred.SecretKey, headers)
+				if err != nil {
+					t.Fatal(err)
+				}
+				req.Header.Set(xhttp.MinIOSourceReplicationRequest, "true")
+				req.Header.Set(xhttp.MinIOSourceMTime, "2100-01-01T00:00:00Z")
+				req.Header.Set(xhttp.MinIOSourceETag, "forged-source-etag")
+				rec := httptest.NewRecorder()
+				router.ServeHTTP(rec, req)
+				oi, err := obj.GetObjectInfo(t.Context(), bucket, "key", ObjectOptions{})
+				if rec.Code != http.StatusOK || err != nil || oi.ModTime.Year() == 2100 || oi.ETag == "forged-source-etag" {
+					t.Fatalf("%s signedMarker=%v: unsigned replication state was accepted: HTTP=%d info=%+v err=%v", backend, signedMarker, rec.Code, oi, err)
+				}
+			}
+		},
+	})
+}
diff --git a/cmd/replication-ssec-retransmit_test.go b/cmd/replication-ssec-retransmit_test.go
index c845b4668..50114d0e7 100644
--- a/cmd/replication-ssec-retransmit_test.go
+++ b/cmd/replication-ssec-retransmit_test.go
@@ -1850,6 +1850,12 @@ func testReplicaLockReconcileNullVersion(obj ObjectLayer, instanceType, bucketNa
 	_ http.Handler, _ auth.Credentials, t *testing.T,
 ) {
 	ctx := t.Context()
+	// A protected retransmit must preserve both the source ciphertext and
+	// its seal. Generate it once for the stored null version and its retry.
+	var ciphertext bytes.Buffer
+	if _, err := sio.Encrypt(&ciphertext, bytes.NewReader([]byte("data")), sio.Config{Key: bytes.Repeat([]byte{1}, 32)}); err != nil {
+		t.Fatal(err)
+	}
 
 	// completeNullMPU runs an SSE-C replica multipart upload addressing the null
 	// version (VersionSuspended) carrying uploadLock, through the reconcile.
@@ -1861,13 +1867,6 @@ func testReplicaLockReconcileNullVersion(obj ObjectLayer, instanceType, bucketNa
 		if err != nil {
 			t.Fatal(err)
 		}
-		// PutObjectPart now validates the DARE stream length (#119). This
-		// object-layer fixture needs an encrypted body before it can exercise
-		// the completion-time null-version metadata reconciliation.
-		var ciphertext bytes.Buffer
-		if _, err := sio.Encrypt(&ciphertext, bytes.NewReader([]byte("data")), sio.Config{Key: bytes.Repeat([]byte{1}, 32)}); err != nil {
-			t.Fatal(err)
-		}
 		part, err := obj.PutObjectPart(ctx, bucketName, object, res.UploadID, 1,
 			mustGetPutObjReader(t, bytes.NewReader(ciphertext.Bytes()), int64(ciphertext.Len()), "", ""), ObjectOptions{})
 		if err != nil {
@@ -1884,8 +1883,9 @@ func testReplicaLockReconcileNullVersion(obj ObjectLayer, instanceType, bucketNa
 		object := "reconcile/null-vs-uuid"
 		// The null version holds a newer legal hold ON@10:00.
 		if _, err := obj.PutObject(ctx, bucketName, object,
-			mustGetPutObjReader(t, bytes.NewReader([]byte("data")), 4, "", ""),
+			mustGetPutObjReader(t, bytes.NewReader(ciphertext.Bytes()), int64(ciphertext.Len()), "", ""),
 			ObjectOptions{VersionSuspended: true, MTime: time.Date(2026, 9, 3, 10, 0, 0, 0, time.UTC), UserDefined: map[string]string{
+				crypto.MetaSealedKeySSEC:                                   "dummy-sealed-key",
 				strings.ToLower(xhttp.AmzObjectLockLegalHold):              "ON",
 				ReservedMetadataPrefixLower + ObjectLockLegalHoldTimestamp: objectLockTestStamp1000,
 			}}); err != nil {
diff --git a/cmd/replication-trust.go b/cmd/replication-trust.go
index 0f8cd5320..c7ba9a674 100644
--- a/cmd/replication-trust.go
+++ b/cmd/replication-trust.go
@@ -13,6 +13,8 @@ package cmd
 import (
 	"context"
 	"net/http"
+	"slices"
+	"strings"
 
 	objectreplication "github.com/minio/minio/internal/bucket/replication"
 	xhttp "github.com/minio/minio/internal/http"
@@ -62,7 +64,7 @@ func isReplicaTrusted(ctx context.Context) bool {
 // grant must not turn client-controlled internal headers into trusted state.
 func replicationPermissionAllowed(ctx context.Context, r *http.Request, bucket, object string, action policy.Action) bool {
 	reqInfo := logger.GetReqInfo(ctx)
-	if reqInfo == nil || reqInfo.Cred.AccessKey == "" {
+	if reqInfo == nil || reqInfo.Cred.AccessKey == "" || !replicationHeadersSigned(r) {
 		return false
 	}
 	reqInfo.BucketName = bucket
@@ -70,6 +72,25 @@ func replicationPermissionAllowed(ctx context.Context, r *http.Request, bucket,
 	return authorizeRequest(ctx, r, action) == ErrNone
 }
 
+// replicationHeadersSigned binds every internal control to the authenticated
+// header signature. Query grants and SigV2 requests cannot confer peer trust.
+// Call only after the request's signature has been verified.
+func replicationHeadersSigned(r *http.Request) bool {
+	if !isRequestSignatureV4(r) || isRequestPresignedSignatureV4(r) {
+		return false
+	}
+	sig, errCode := parseSignV4(r.Header.Get(xhttp.Authorization), globalSite.Region(), serviceS3)
+	if errCode != ErrNone {
+		return false
+	}
+	for _, name := range replicationRequestHeaders {
+		if _, present := r.Header[http.CanonicalHeaderKey(name)]; present && !slices.Contains(sig.SignedHeaders, strings.ToLower(name)) {
+			return false
+		}
+	}
+	return true
+}
+
 // evaluateReplicationTrust decides whether a request may carry replication
 // semantics for the given action. A request that declares itself a replica
 // without holding the replication permission is rejected. trusted reports that
diff --git a/cmd/s3-zip-handlers.go b/cmd/s3-zip-handlers.go
index b7fe426bf..62ae864e1 100644
--- a/cmd/s3-zip-handlers.go
+++ b/cmd/s3-zip-handlers.go
@@ -144,13 +144,7 @@ func (api objectAPIHandlers) getObjectInArchiveFileHandler(ctx context.Context,
 
 	zipInfo := zipObjInfo.ArchiveInfo(r.Header)
 	if len(zipInfo) == 0 {
-		opts.EncryptFn, err = zipObjInfo.metadataEncryptFn(r.Header)
-		if err != nil {
-			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
-			return
-		}
-
-		zipInfo, err = updateObjectMetadataWithZipInfo(ctx, objectAPI, bucket, zipPath, opts)
+		zipInfo, _, err = readObjectZIPInfo(ctx, objectAPI, bucket, zipPath, opts)
 	}
 	if err != nil {
 		writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
@@ -245,8 +239,7 @@ func listObjectsV2InArchive(ctx context.Context, objectAPI ObjectLayer, bucket,
 
 	zipInfo := zipObjInfo.ArchiveInfo(h)
 	if len(zipInfo) == 0 {
-		// Always update the latest version
-		zipInfo, err = updateObjectMetadataWithZipInfo(ctx, objectAPI, bucket, zipPath, ObjectOptions{})
+		zipInfo, _, err = readObjectZIPInfo(ctx, objectAPI, bucket, zipPath, ObjectOptions{})
 	}
 	if err != nil {
 		return ListObjectsV2Info{}, err
@@ -437,12 +430,7 @@ func (api objectAPIHandlers) headObjectInArchiveFileHandler(ctx context.Context,
 
 	zipInfo := zipObjInfo.ArchiveInfo(r.Header)
 	if len(zipInfo) == 0 {
-		opts.EncryptFn, err = zipObjInfo.metadataEncryptFn(r.Header)
-		if err != nil {
-			writeErrorResponseHeadersOnly(w, toAPIError(ctx, err))
-			return
-		}
-		zipInfo, err = updateObjectMetadataWithZipInfo(ctx, objectAPI, bucket, zipPath, opts)
+		zipInfo, _, err = readObjectZIPInfo(ctx, objectAPI, bucket, zipPath, opts)
 	}
 	if err != nil {
 		writeErrorResponseHeadersOnly(w, toAPIError(ctx, err))
@@ -482,15 +470,22 @@ func (api objectAPIHandlers) headObjectInArchiveFileHandler(ctx context.Context,
 	w.WriteHeader(http.StatusOK)
 }
 
-// Update the passed zip object metadata with the zip contents info, file name, modtime, size, etc.
-// The returned zip index will de decrypted.
-func updateObjectMetadataWithZipInfo(ctx context.Context, objectAPI ObjectLayer, bucket, object string, opts ObjectOptions) ([]byte, error) {
+// readObjectZIPInfo builds an index without modifying the object. A GET, HEAD
+// or archive listing must remain read-only even when no index was stored.
+func readObjectZIPInfo(ctx context.Context, objectAPI ObjectLayer, bucket, object string, opts ObjectOptions) ([]byte, ObjectInfo, error) {
 	files, srcInfo, err := getFilesListFromZIPObject(ctx, objectAPI, bucket, object, opts)
 	if err != nil {
-		return nil, err
+		return nil, srcInfo, err
 	}
 	files.OptimizeSize()
 	zipInfo, err := files.Serialize()
+	return zipInfo, srcInfo, err
+}
+
+// updateObjectMetadataWithZipInfo persists an index only for upload operations
+// that explicitly request extraction. The returned index is decrypted.
+func updateObjectMetadataWithZipInfo(ctx context.Context, objectAPI ObjectLayer, bucket, object string, opts ObjectOptions) ([]byte, error) {
+	zipInfo, srcInfo, err := readObjectZIPInfo(ctx, objectAPI, bucket, object, opts)
 	if err != nil {
 		return nil, err
 	}
@@ -500,7 +495,6 @@ func updateObjectMetadataWithZipInfo(ctx context.Context, objectAPI ObjectLayer,
 		at = archiveTypeEnc
 		zipInfoStr = string(opts.EncryptFn(archiveTypeEnc, zipInfo))
 	}
-	srcInfo.UserDefined[archiveTypeMetadataKey] = at
 	popts := ObjectOptions{
 		MTime:     srcInfo.ModTime,
 		VersionID: srcInfo.VersionID,
diff --git a/cmd/s3-zip-readonly_test.go b/cmd/s3-zip-readonly_test.go
new file mode 100644
index 000000000..22c2b5e78
--- /dev/null
+++ b/cmd/s3-zip-readonly_test.go
@@ -0,0 +1,109 @@
+// Copyright (c) 2026 Feng Ruohang
+//
+// This file is part of Silo Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"archive/zip"
+	"bytes"
+	"fmt"
+	"maps"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/minio/minio/internal/auth"
+)
+
+func TestAPIArchiveReadsDoNotPersistMetadata(t *testing.T) {
+	defer DetectTestLeak(t)()
+	ExecObjectLayerAPITest(ExecObjectLayerAPITestArgs{
+		t: t, makeBucketOptions: MakeBucketOptions{LockEnabled: true},
+		objAPITest: func(obj ObjectLayer, backend, bucket string, router http.Handler, cred auth.Credentials, t *testing.T) {
+			var archive bytes.Buffer
+			zw := zip.NewWriter(&archive)
+			file, err := zw.Create("entry.txt")
+			if err != nil {
+				t.Fatal(err)
+			}
+			if _, err = file.Write([]byte("archive content")); err != nil {
+				t.Fatal(err)
+			}
+			if err = zw.Close(); err != nil {
+				t.Fatal(err)
+			}
+			reader := newObjectAttributesAuthzUser(t, backend, bucket, `"s3:GetObject","s3:ListBucket"`)
+			policy := fmt.Appendf(nil, `{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Principal":"*","Action":["s3:GetObject","s3:ListBucket"],"Resource":["arn:aws:s3:::%s","arn:aws:s3:::%s/*"]}]}`, bucket, bucket)
+			if _, err = globalBucketMetadataSys.Update(t.Context(), bucket, bucketPolicyConfig, policy); err != nil {
+				t.Fatal(err)
+			}
+			for _, anonymous := range []bool{false, true} {
+				for _, method := range []string{http.MethodGet, http.MethodHead, "LIST"} {
+					key := fmt.Sprintf("archive-%v-%s.zip", anonymous, method)
+					before, err := obj.PutObject(t.Context(), bucket, key, mustGetPutObjReader(t, bytes.NewReader(archive.Bytes()), int64(archive.Len()), "", ""), ObjectOptions{Versioned: true, UserDefined: batchLockMeta("COMPLIANCE")})
+					if err != nil {
+						t.Fatal(err)
+					}
+					before, err = obj.GetObjectInfo(t.Context(), bucket, key, ObjectOptions{VersionID: before.VersionID})
+					if err != nil {
+						t.Fatal(err)
+					}
+					url := getGetObjectURL("", bucket, key+"/entry.txt")
+					verb := method
+					if method == "LIST" {
+						verb = http.MethodGet
+						url = "/" + bucket + "?list-type=2&prefix=" + key + "/"
+					}
+					req, err := newTestSignedRequestV4(verb, url, 0, nil, reader.AccessKey, reader.SecretKey, map[string]string{xMinIOExtract: "true"})
+					if err != nil {
+						t.Fatal(err)
+					}
+					if anonymous {
+						req.Header.Del("Authorization")
+					}
+					rec := httptest.NewRecorder()
+					router.ServeHTTP(rec, req)
+					if rec.Code != http.StatusOK {
+						t.Fatalf("%s anonymous=%v %s: %d %s", backend, anonymous, method, rec.Code, rec.Body.String())
+					}
+					if method == http.MethodGet && rec.Body.String() != "archive content" {
+						t.Fatalf("wrong archive entry: %s", rec.Body.String())
+					}
+					if method == "LIST" && !bytes.Contains(rec.Body.Bytes(), []byte("entry.txt")) {
+						t.Fatal("archive listing omitted entry")
+					}
+					after, err := obj.GetObjectInfo(t.Context(), bucket, key, ObjectOptions{VersionID: before.VersionID})
+					if err != nil || !maps.Equal(before.UserDefined, after.UserDefined) || !after.ModTime.Equal(before.ModTime) || after.ETag != before.ETag {
+						t.Fatalf("%s anonymous=%v %s changed stored metadata: before=%v after=%v err=%v", backend, anonymous, method, before.UserDefined, after.UserDefined, err)
+					}
+				}
+			}
+			// Explicit extraction during an authorized upload still builds and
+			// persists the index for subsequent reads.
+			req, err := newTestSignedRequestV4(http.MethodPut, getPutObjectURL("", bucket, "indexed.zip"), int64(archive.Len()), bytes.NewReader(archive.Bytes()), cred.AccessKey, cred.SecretKey, map[string]string{xMinIOExtract: "true"})
+			if err != nil {
+				t.Fatal(err)
+			}
+			rec := httptest.NewRecorder()
+			router.ServeHTTP(rec, req)
+			oi, err := obj.GetObjectInfo(t.Context(), bucket, "indexed.zip", ObjectOptions{})
+			if rec.Code != http.StatusOK || err != nil || len(oi.ArchiveInfo(nil)) == 0 {
+				t.Fatalf("explicit extraction lost index: %d %s %v", rec.Code, rec.Body.String(), err)
+			}
+		},
+	})
+}
diff --git a/cmd/streaming-auth-boundary_test.go b/cmd/streaming-auth-boundary_test.go
new file mode 100644
index 000000000..2daeb43bb
--- /dev/null
+++ b/cmd/streaming-auth-boundary_test.go
@@ -0,0 +1,114 @@
+// Copyright (c) 2026 Feng Ruohang
+//
+// This file is part of Silo Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+package cmd
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/minio/minio/internal/auth"
+	xhttp "github.com/minio/minio/internal/http"
+)
+
+func TestAPIStreamingAuthenticationBoundaries(t *testing.T) {
+	defer DetectTestLeak(t)()
+	ExecObjectLayerAPITest(ExecObjectLayerAPITestArgs{
+		t: t, endpoints: []string{"PutObject"},
+		objAPITest: func(obj ObjectLayer, backend, bucket string, router http.Handler, cred auth.Credentials, t *testing.T) {
+			data := []byte("authenticated streaming payload")
+			for _, mode := range []string{"valid", "missing-algorithm", "wrong-algorithm", "wrong-signature"} {
+				req, err := newStreamingUnsignedTrailerRequest(http.MethodPut, getPutObjectURL("", bucket, mode), data, UTCNow())
+				if err != nil {
+					t.Fatal(err)
+				}
+				if err := signRequestV4(req, cred.AccessKey, cred.SecretKey); err != nil {
+					t.Fatal(err)
+				}
+				authorization := req.Header.Get(xhttp.Authorization)
+				switch mode {
+				case "missing-algorithm":
+					authorization = strings.TrimPrefix(authorization, signV4Algorithm+" ")
+				case "wrong-algorithm":
+					authorization = strings.Replace(authorization, signV4Algorithm, "INVALID", 1)
+				case "wrong-signature":
+					prefix, _, found := strings.Cut(authorization, "Signature=")
+					if !found {
+						t.Fatal("signed request has no signature")
+					}
+					authorization = prefix + "Signature=" + strings.Repeat("0", 64)
+				}
+				req.Header.Set(xhttp.Authorization, authorization)
+				rec := httptest.NewRecorder()
+				router.ServeHTTP(rec, req)
+				_, stored := obj.GetObjectInfo(t.Context(), bucket, mode, ObjectOptions{})
+				if mode == "valid" {
+					if rec.Code != http.StatusOK || stored != nil {
+						t.Fatalf("%s %s: %d %s, object: %v", backend, mode, rec.Code, rec.Body.String(), stored)
+					}
+				} else if rec.Code < 400 || stored == nil {
+					t.Errorf("%s %s: malformed authentication wrote an object: %d %s", backend, mode, rec.Code, rec.Body.String())
+				}
+			}
+			for _, trailers := range []bool{false, true} {
+				req, err := newTestStreamingSignedRequest(http.MethodPut, getPutObjectURL("", bucket, "tagged"), int64(len(data)), 64*1024, bytes.NewReader(data), cred.AccessKey, cred.SecretKey)
+				if err != nil {
+					t.Fatal(err)
+				}
+				if trailers {
+					req.Header.Set(xhttp.AmzContentSha256, streamingContentSHA256Trailer)
+					req.Header.Set(awsTrailerHeader, "x-amz-checksum-crc32")
+					if err := signRequestV4(req, cred.AccessKey, cred.SecretKey); err != nil {
+						t.Fatal(err)
+					}
+				}
+				getRequestAuthType(req)
+				if _, _, _, _, code := calculateSeedSignature(req, trailers); code != ErrNone {
+					t.Fatalf("%s trailers=%v: valid seed rejected: %v", backend, trailers, code)
+				}
+				req.Header.Set(xhttp.AmzObjectTagging, "unsigned=injected")
+				if _, code := newSignV4ChunkedReader(req, trailers); code != ErrUnsignedHeaders {
+					t.Errorf("%s trailers=%v: unsigned tags accepted: %v", backend, trailers, code)
+				}
+				rec := httptest.NewRecorder()
+				router.ServeHTTP(rec, req)
+				if _, err := obj.GetObjectInfo(t.Context(), bucket, "tagged", ObjectOptions{}); rec.Code < 400 || err == nil {
+					t.Errorf("%s trailers=%v: injected metadata stored: %d", backend, trailers, rec.Code)
+				}
+			}
+			// A public bucket can still use the unsigned trailer decoder without
+			// claiming credentials; authorization remains the handler's job.
+			req, err := newStreamingUnsignedTrailerRequest(http.MethodPut, "/public/key", data, UTCNow())
+			if err != nil {
+				t.Fatal(err)
+			}
+			rd, code := newUnsignedV4ChunkedReader(req, true)
+			if code != ErrNone {
+				t.Fatal(code)
+			}
+			got, err := io.ReadAll(rd)
+			rd.Close()
+			if err != nil || !bytes.Equal(got, data) {
+				t.Fatalf("anonymous decoder: %q %v", got, err)
+			}
+		},
+	})
+}
diff --git a/cmd/streaming-signature-v4.go b/cmd/streaming-signature-v4.go
index 702714be0..eef479a0c 100644
--- a/cmd/streaming-signature-v4.go
+++ b/cmd/streaming-signature-v4.go
@@ -127,6 +127,9 @@ func calculateSeedSignature(r *http.Request, trailers bool) (cred auth.Credentia
 	if errCode != ErrNone {
 		return cred, "", "", time.Time{}, errCode
 	}
+	if errCode := checkUnsignedHeaders(extractedSignedHeaders, r); errCode != ErrNone {
+		return cred, "", "", time.Time{}, errCode
+	}
 
 	cred, _, errCode = checkKeyValid(r, signV4Values.Credential.accessKey)
 	if errCode != ErrNone {
diff --git a/cmd/streaming-v4-unsigned.go b/cmd/streaming-v4-unsigned.go
index 04014c5c5..11c524a3a 100644
--- a/cmd/streaming-v4-unsigned.go
+++ b/cmd/streaming-v4-unsigned.go
@@ -24,6 +24,8 @@ import (
 	"io"
 	"net/http"
 	"strings"
+
+	xhttp "github.com/minio/minio/internal/http"
 )
 
 // newUnsignedV4ChunkedReader returns a new s3UnsignedChunkedReader that translates
@@ -42,8 +44,10 @@ func newUnsignedV4ChunkedReader(req *http.Request, trailer bool) (io.ReadCloser,
 	if isRequestPresignedSignatureV4(req) {
 		return nil, ErrSignatureVersionNotSupported
 	}
-	if isRequestSignatureV4(req) {
-		if errCode := reqSignatureV4Verify(req, globalSite.Region(), serviceS3); errCode != ErrNone {
+	// Any claimed header credential must pass the complete SigV4 parser. The
+	// streaming auth classification does not require the algorithm prefix.
+	if req.Header.Get(xhttp.Authorization) != "" {
+		if errCode := doesSignatureMatch(unsignedPayloadTrailer, req, globalSite.Region(), serviceS3); errCode != ErrNone {
 			return nil, errCode
 		}
 	}