diff --git a/cmd/auth-handler.go b/cmd/auth-handler.go
index 6e824e312..e1e54d650 100644
--- a/cmd/auth-handler.go
+++ b/cmd/auth-handler.go
@@ -343,6 +343,26 @@ func checkRequestAuthType(ctx context.Context, r *http.Request, action policy.Ac
 	return s3Err
 }
 
+func checkRequestAuthTypeWithExistingTags(ctx context.Context, r *http.Request, action policy.Action, bucketName, objectName, existingTags string) (s3Err APIErrorCode) {
+	logger.GetReqInfo(ctx).BucketName = bucketName
+	logger.GetReqInfo(ctx).ObjectName = objectName
+
+	if s3Err = authenticateRequest(ctx, r, action); s3Err != ErrNone {
+		return s3Err
+	}
+	return authorizeRequestWithExistingTags(ctx, r, action, existingTags)
+}
+
+func checkRequestAuthTypeWithRequestTags(ctx context.Context, r *http.Request, action policy.Action, bucketName, objectName string, requestTags *string) (s3Err APIErrorCode) {
+	logger.GetReqInfo(ctx).BucketName = bucketName
+	logger.GetReqInfo(ctx).ObjectName = objectName
+
+	if s3Err = authenticateRequest(ctx, r, action); s3Err != ErrNone {
+		return s3Err
+	}
+	return authorizeRequestWithTags(ctx, r, action, "", requestTags)
+}
+
 // checkRequestAuthTypeWithVID is similar to checkRequestAuthType
 // passes versionID additionally.
 func checkRequestAuthTypeWithVID(ctx context.Context, r *http.Request, action policy.Action, bucketName, objectName, versionID string) (s3Err APIErrorCode) {
@@ -416,6 +436,14 @@ func authenticateRequest(ctx context.Context, r *http.Request, action policy.Act
 }
 
 func authorizeRequest(ctx context.Context, r *http.Request, action policy.Action) (s3Err APIErrorCode) {
+	return authorizeRequestWithExistingTags(ctx, r, action, "")
+}
+
+func authorizeRequestWithExistingTags(ctx context.Context, r *http.Request, action policy.Action, existingTags string) (s3Err APIErrorCode) {
+	return authorizeRequestWithTags(ctx, r, action, existingTags, nil)
+}
+
+func authorizeRequestWithTags(ctx context.Context, r *http.Request, action policy.Action, existingTags string, requestTags *string) (s3Err APIErrorCode) {
 	reqInfo := logger.GetReqInfo(ctx)
 	if reqInfo == nil {
 		return ErrAccessDenied
@@ -435,7 +463,7 @@ func authorizeRequest(ctx context.Context, r *http.Request, action policy.Action
 			Groups:          cred.Groups,
 			Action:          action,
 			BucketName:      bucket,
-			ConditionValues: getConditionValues(r, region, auth.AnonymousCredentials),
+			ConditionValues: getConditionValuesWithTags(r, region, auth.AnonymousCredentials, existingTags, requestTags),
 			IsOwner:         false,
 			ObjectName:      object,
 		}) {
@@ -451,7 +479,7 @@ func authorizeRequest(ctx context.Context, r *http.Request, action policy.Action
 				Groups:          cred.Groups,
 				Action:          policy.ListBucketAction,
 				BucketName:      bucket,
-				ConditionValues: getConditionValues(r, region, auth.AnonymousCredentials),
+				ConditionValues: getConditionValuesWithTags(r, region, auth.AnonymousCredentials, existingTags, requestTags),
 				IsOwner:         false,
 				ObjectName:      object,
 			}) {
@@ -468,7 +496,7 @@ func authorizeRequest(ctx context.Context, r *http.Request, action policy.Action
 			Groups:          cred.Groups,
 			Action:          policy.Action(policy.DeleteObjectVersionAction),
 			BucketName:      bucket,
-			ConditionValues: getConditionValues(r, "", cred),
+			ConditionValues: getConditionValuesWithTags(r, "", cred, existingTags, requestTags),
 			ObjectName:      object,
 			IsOwner:         owner,
 			Claims:          cred.Claims,
@@ -482,7 +510,7 @@ func authorizeRequest(ctx context.Context, r *http.Request, action policy.Action
 		Groups:          cred.Groups,
 		Action:          action,
 		BucketName:      bucket,
-		ConditionValues: getConditionValues(r, "", cred),
+		ConditionValues: getConditionValuesWithTags(r, "", cred, existingTags, requestTags),
 		ObjectName:      object,
 		IsOwner:         owner,
 		Claims:          cred.Claims,
@@ -499,7 +527,7 @@ func authorizeRequest(ctx context.Context, r *http.Request, action policy.Action
 			Groups:          cred.Groups,
 			Action:          policy.ListBucketAction,
 			BucketName:      bucket,
-			ConditionValues: getConditionValues(r, "", cred),
+			ConditionValues: getConditionValuesWithTags(r, "", cred, existingTags, requestTags),
 			ObjectName:      object,
 			IsOwner:         owner,
 			Claims:          cred.Claims,
@@ -720,6 +748,10 @@ func isPutRetentionAllowed(bucketName, objectName string, retDays int, retDate t
 // call verifies bucket policies and IAM policies, supports multi user
 // checks etc.
 func isPutActionAllowed(ctx context.Context, atype authType, bucketName, objectName string, r *http.Request, action policy.Action) (s3Err APIErrorCode) {
+	return isPutActionAllowedWithRequestTags(ctx, atype, bucketName, objectName, r, action, nil)
+}
+
+func isPutActionAllowedWithRequestTags(ctx context.Context, atype authType, bucketName, objectName string, r *http.Request, action policy.Action, requestTags *string) (s3Err APIErrorCode) {
 	var cred auth.Credentials
 	var owner bool
 	region := globalSite.Region()
@@ -760,7 +792,7 @@ func isPutActionAllowed(ctx context.Context, atype authType, bucketName, objectN
 			Groups:          cred.Groups,
 			Action:          action,
 			BucketName:      bucketName,
-			ConditionValues: getConditionValues(r, "", auth.AnonymousCredentials),
+			ConditionValues: getConditionValuesWithTags(r, "", auth.AnonymousCredentials, "", requestTags),
 			IsOwner:         false,
 			ObjectName:      objectName,
 		}) {
@@ -774,7 +806,7 @@ func isPutActionAllowed(ctx context.Context, atype authType, bucketName, objectN
 		Groups:          cred.Groups,
 		Action:          action,
 		BucketName:      bucketName,
-		ConditionValues: getConditionValues(r, "", cred),
+		ConditionValues: getConditionValuesWithTags(r, "", cred, "", requestTags),
 		ObjectName:      objectName,
 		IsOwner:         owner,
 		Claims:          cred.Claims,
diff --git a/cmd/bucket-policy.go b/cmd/bucket-policy.go
index 0bcbe2e66..d096705b2 100644
--- a/cmd/bucket-policy.go
+++ b/cmd/bucket-policy.go
@@ -34,6 +34,7 @@ import (
 	xhttp "github.com/minio/minio/internal/http"
 	"github.com/minio/minio/internal/logger"
 	"github.com/minio/pkg/v3/policy"
+	"github.com/minio/pkg/v3/policy/condition"
 )
 
 // PolicySys - policy subsystem.
@@ -75,7 +76,104 @@ func getSTSConditionValues(r *http.Request, lc string, cred auth.Credentials) ma
 	return m
 }
 
+type conditionValueSource uint8
+
+const (
+	conditionValueFromHeader conditionValueSource = 1 << iota
+	conditionValueFromQuery
+)
+
+// clientSuppliedConditionKeys records where each request-derived condition
+// value actually comes from. Most x-amz-* values are headers, list parameters
+// are query-only, and storage class retains the compatible query form consumed
+// by object operations.
+var clientSuppliedConditionKeys = map[string]conditionValueSource{
+	"prefix":    conditionValueFromQuery,
+	"delimiter": conditionValueFromQuery,
+	"max-keys":  conditionValueFromQuery,
+	// AWS explicitly excludes the query-string form from this policy key,
+	// even though MinIO may consume it separately while verifying a presign.
+	"x-amz-content-sha256":                            conditionValueFromHeader,
+	"x-amz-copy-source":                               conditionValueFromHeader,
+	"x-amz-metadata-directive":                        conditionValueFromHeader,
+	"x-amz-server-side-encryption":                    conditionValueFromHeader,
+	"x-amz-server-side-encryption-aws-kms-key-id":     conditionValueFromHeader,
+	"x-amz-server-side-encryption-customer-algorithm": conditionValueFromHeader,
+	"x-amz-storage-class":                             conditionValueFromHeader | conditionValueFromQuery,
+}
+
+func acceptsConditionValueSource(key string, source conditionValueSource) bool {
+	name := strings.ToLower(key)
+	allowed, ok := clientSuppliedConditionKeys[name]
+	if !ok {
+		return true
+	}
+	if allowed&source == 0 {
+		return false
+	}
+	return source != conditionValueFromQuery || key == name
+}
+
+// internalConditionKeys holds every other name a condition key can resolve to.
+// Those name values MinIO derives for itself - identity from the credential,
+// time from the clock, transport from the connection - and a request must never
+// write one, whether or not the server populated it this time round: a name the
+// server left empty is as forgeable as one it filled in, and the condition
+// reading it cannot tell the difference.
+//
+// Deriving the set from the condition keys rather than from what
+// getConditionValues writes is what makes it complete. The engine reads by key
+// name, so the key list is the attack surface; enumerating the writes misses
+// every key the server has no value for, which is most of jwt: and ldap:. It
+// also defaults new upstream keys to reserved, which is the safe direction.
+//
+// Reserving a name only removes it from the condition map. Request handling is
+// untouched - a handler still reads its own query parameters and headers.
+//
+// aws:SourceIp is still only as trustworthy as the forwarding headers it is
+// computed from, see the note on GetSourceIPFromHeaders.
+var internalConditionKeys = func() map[string]struct{} {
+	keys := make(map[string]struct{}, 2*len(condition.AllSupportedKeys))
+	for _, keyName := range condition.AllSupportedKeys {
+		name := keyName.ToKey().Name()
+		if _, clientSupplied := clientSuppliedConditionKeys[name]; clientSupplied {
+			continue
+		}
+		// A condition key resolves against its exact name and falls back to the
+		// canonical MIME form, so both spellings have to be held. This is also
+		// what covers object lock, stored as Object-Lock-Mode and read as
+		// s3:object-lock-mode.
+		keys[name] = struct{}{}
+		keys[http.CanonicalHeaderKey(name)] = struct{}{}
+	}
+	return keys
+}()
+
+// Tag conditions name one tag key each, so the variable forms are reserved by
+// prefix; the bare names come from the loop above.
+var internalConditionKeyPrefixes = []string{"ExistingObjectTag/", "RequestObjectTag/"}
+
+func isInternalConditionKey(key string) bool {
+	if _, ok := internalConditionKeys[key]; ok {
+		return true
+	}
+	for _, prefix := range internalConditionKeyPrefixes {
+		if strings.HasPrefix(key, prefix) {
+			return true
+		}
+	}
+	return false
+}
+
 func getConditionValues(r *http.Request, lc string, cred auth.Credentials) map[string][]string {
+	return getConditionValuesWithExistingTags(r, lc, cred, "")
+}
+
+func getConditionValuesWithExistingTags(r *http.Request, lc string, cred auth.Credentials, existingTags string) map[string][]string {
+	return getConditionValuesWithTags(r, lc, cred, existingTags, nil)
+}
+
+func getConditionValuesWithTags(r *http.Request, lc string, cred auth.Credentials, existingTags string, requestTags *string) map[string][]string {
 	currTime := UTCNow()
 
 	var (
@@ -144,26 +242,44 @@ func getConditionValues(r *http.Request, lc string, cred auth.Credentials) map[s
 	if lc != "" {
 		args["LocationConstraint"] = []string{lc}
 	}
-
-	cloneHeader := r.Header.Clone()
-	if v := cloneHeader.Get("x-amz-signature-age"); v != "" {
-		args["signatureAge"] = []string{v}
-		cloneHeader.Del("x-amz-signature-age")
+	if storageClass, ok := getRequestHeaderOrQueryValue(r, xhttp.AmzStorageClass); ok {
+		args[strings.ToLower(xhttp.AmzStorageClass)] = []string{storageClass}
 	}
 
-	if userTags := cloneHeader.Get(xhttp.AmzObjectTagging); userTags != "" {
+	cloneHeader := r.Header.Clone()
+	signatureAge := cloneHeader.Get("x-amz-signature-age")
+	cloneHeader.Del("x-amz-signature-age")
+	// The presigned V4 verifier overwrites this internal scratch header after
+	// validating the signature. Ignore a value supplied on every other request
+	// type, where it would otherwise synthesize s3:signatureAge.
+	if authType == authTypePresigned && signatureAge != "" {
+		args["signatureAge"] = []string{signatureAge}
+	}
+
+	userTags := cloneHeader.Get(xhttp.AmzObjectTagging)
+	if requestTags != nil {
+		userTags = *requestTags
+	}
+	if userTags != "" {
 		tag, _ := tags.ParseObjectTags(userTags)
 		if tag != nil {
 			tagMap := tag.ToMap()
 			keys := make([]string, 0, len(tagMap))
 			for k, v := range tagMap {
-				args[pathJoin("ExistingObjectTag", k)] = []string{v}
 				args[pathJoin("RequestObjectTag", k)] = []string{v}
 				keys = append(keys, k)
 			}
 			args["RequestObjectTagKeys"] = keys
 		}
 	}
+	if existingTags != "" {
+		tag, _ := tags.ParseObjectTags(existingTags)
+		if tag != nil {
+			for k, v := range tag.ToMap() {
+				args[pathJoin("ExistingObjectTag", k)] = []string{v}
+			}
+		}
+	}
 
 	for _, objLock := range []string{
 		xhttp.AmzObjectLockMode,
@@ -176,8 +292,20 @@ func getConditionValues(r *http.Request, lc string, cred auth.Credentials) map[s
 		cloneHeader.Del(objLock)
 	}
 
+	// The two loops below fold raw header and query values into the same map
+	// the server just filled in. Anything they add is indistinguishable, to a
+	// condition, from a value the server derived - and they merge by appending,
+	// so a supplied entry sits alongside the real one rather than replacing it.
+	// The source check keeps headers and query parameters in their actual roles;
+	// isInternalConditionKey keeps both apart from server-derived values.
 	for key, values := range cloneHeader {
-		if strings.EqualFold(key, xhttp.AmzObjectTagging) {
+		if strings.EqualFold(key, xhttp.AmzObjectTagging) || strings.EqualFold(key, xhttp.AmzStorageClass) {
+			continue
+		}
+		if !acceptsConditionValueSource(key, conditionValueFromHeader) {
+			continue
+		}
+		if isInternalConditionKey(key) {
 			continue
 		}
 		if existingValues, found := args[key]; found {
@@ -190,18 +318,16 @@ func getConditionValues(r *http.Request, lc string, cred auth.Credentials) map[s
 	cloneURLValues := make(url.Values, len(r.Form))
 	maps.Copy(cloneURLValues, r.Form)
 
-	for _, objLock := range []string{
-		xhttp.AmzObjectLockMode,
-		xhttp.AmzObjectLockLegalHold,
-		xhttp.AmzObjectLockRetainUntilDate,
-	} {
-		if values, ok := cloneURLValues[objLock]; ok {
-			args[strings.TrimPrefix(objLock, "X-Amz-")] = values
-		}
-		cloneURLValues.Del(objLock)
-	}
-
 	for key, values := range cloneURLValues {
+		if strings.EqualFold(key, xhttp.AmzObjectTagging) || strings.EqualFold(key, xhttp.AmzStorageClass) {
+			continue
+		}
+		if !acceptsConditionValueSource(key, conditionValueFromQuery) {
+			continue
+		}
+		if isInternalConditionKey(key) {
+			continue
+		}
 		if existingValues, found := args[key]; found {
 			args[key] = append(existingValues, values...)
 		} else {
diff --git a/cmd/bucket-policy_test.go b/cmd/bucket-policy_test.go
new file mode 100644
index 000000000..4e24d3e6c
--- /dev/null
+++ b/cmd/bucket-policy_test.go
@@ -0,0 +1,482 @@
+// Copyright (c) 2015-2026 MinIO, Inc.
+//
+// This file is part of MinIO 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 (
+	"net"
+	"net/http"
+	"net/url"
+	"slices"
+	"strings"
+	"testing"
+
+	"github.com/minio/minio/internal/auth"
+	xhttp "github.com/minio/minio/internal/http"
+	"github.com/minio/pkg/v3/policy"
+	"github.com/minio/pkg/v3/policy/condition"
+)
+
+const (
+	testCondSourceIP  = "203.0.113.5"
+	testCondRemoteILP = testCondSourceIP + ":12345"
+)
+
+func condValuesForRequest(t *testing.T, rawURL string, header map[string]string) map[string][]string {
+	return condValuesForRequestWithTags(t, rawURL, header, "", nil)
+}
+
+func condValuesForRequestWithExistingTags(t *testing.T, rawURL string, header map[string]string, existingTags string) map[string][]string {
+	return condValuesForRequestWithTags(t, rawURL, header, existingTags, nil)
+}
+
+func condValuesForRequestWithTags(t *testing.T, rawURL string, header map[string]string, existingTags string, requestTags *string) map[string][]string {
+	t.Helper()
+	r, err := http.NewRequest(http.MethodGet, rawURL, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.RemoteAddr = testCondRemoteILP
+	for k, v := range header {
+		r.Header.Set(k, v)
+	}
+	if err := r.ParseForm(); err != nil {
+		t.Fatal(err)
+	}
+	return getConditionValuesWithTags(r, "us-east-1", auth.Credentials{AccessKey: "lowpriv"}, existingTags, requestTags)
+}
+
+func resolvedConditionValues(values map[string][]string, name string) []string {
+	if v := values[name]; len(v) > 0 {
+		return v
+	}
+	return values[http.CanonicalHeaderKey(name)]
+}
+
+// A client must not be able to reach a condition key that the server computes
+// for itself. Both routes are covered: a header whose canonical spelling
+// collides with the key name, and a query parameter that collides with it
+// exactly. The query route is the sharper one, because the merge appended to
+// the server's value rather than replacing it and a condition function matches
+// when any single value matches.
+func TestGetConditionValuesRejectsClientSuppliedServerKeys(t *testing.T) {
+	honest := condValuesForRequest(t, "http://minio.local/bkt/obj", nil)
+
+	for _, kn := range condition.AllSupportedKeys {
+		name := kn.ToKey().Name()
+		if _, clientSupplied := clientSuppliedConditionKeys[name]; clientSupplied {
+			continue // the request is where this one is supposed to come from
+		}
+		// Deliberately not skipped when the server left the key empty. An empty
+		// name is exactly as forgeable as a populated one, and the keys the
+		// server has no value for - most of jwt: and ldap: - are the ones a
+		// resource variable expands.
+		want := honest[name]
+		canonical := http.CanonicalHeaderKey(name)
+
+		t.Run("query/"+name, func(t *testing.T) {
+			got := condValuesForRequest(t,
+				"http://minio.local/bkt/obj?"+url.Values{name: {"ATTACKER"}}.Encode(), nil)
+			if slices.Contains(got[name], "ATTACKER") {
+				t.Errorf("?%s= reached %v, server computed %v", name, got[name], want)
+			}
+			if !slices.Equal(got[name], want) {
+				t.Errorf("%v changed to %v", want, got[name])
+			}
+		})
+
+		// aws:Referer is read out of the Referer header, so the header is its
+		// source of truth rather than a way to forge it. aws:UserAgent is not
+		// in the same position: it comes from User-Agent, which does not
+		// canonicalise to "Useragent".
+		if kn == condition.AWSReferer {
+			continue
+		}
+
+		t.Run("header/"+canonical, func(t *testing.T) {
+			got := condValuesForRequest(t, "http://minio.local/bkt/obj",
+				map[string]string{canonical: "ATTACKER"})
+			// The lookup the policy engine itself performs, exact name first
+			// with the canonical form as fallback.
+			seen := got[name]
+			if len(seen) == 0 {
+				seen = got[canonical]
+			}
+			if slices.Contains(seen, "ATTACKER") {
+				t.Errorf("%s: header reached the lookup as %v, server computed %v",
+					canonical, seen, want)
+			}
+		})
+	}
+}
+
+func TestGetConditionValuesUsesActualRequestSource(t *testing.T) {
+	for name, source := range clientSuppliedConditionKeys {
+		t.Run(name, func(t *testing.T) {
+			fromHeader := condValuesForRequest(t, "http://minio.local/bkt/obj",
+				map[string]string{name: "HEADER"})
+			fromQuery := condValuesForRequest(t,
+				"http://minio.local/bkt/obj?"+url.Values{name: {"QUERY"}}.Encode(), nil)
+			fromCanonicalQuery := condValuesForRequest(t,
+				"http://minio.local/bkt/obj?"+url.Values{http.CanonicalHeaderKey(name): {"QUERY"}}.Encode(), nil)
+			if got, want := slices.Contains(resolvedConditionValues(fromHeader, name), "HEADER"), source&conditionValueFromHeader != 0; got != want {
+				t.Errorf("header accepted=%v, want %v: %v", got, want, fromHeader)
+			}
+			if got, want := slices.Contains(resolvedConditionValues(fromQuery, name), "QUERY"), source&conditionValueFromQuery != 0; got != want {
+				t.Errorf("query accepted=%v, want %v: %v", got, want, fromQuery)
+			}
+			canonicalQueryAllowed := name == strings.ToLower(xhttp.AmzStorageClass)
+			if got := slices.Contains(resolvedConditionValues(fromCanonicalQuery, name), "QUERY"); got != canonicalQueryAllowed {
+				t.Errorf("case-variant query accepted=%v, want %v: %v", got, canonicalQueryAllowed, fromCanonicalQuery)
+			}
+		})
+	}
+
+	storageURL := "http://minio.local/bkt/obj?" + url.Values{
+		strings.ToLower(xhttp.AmzStorageClass): {"QUERY"},
+	}.Encode()
+	storageValues := condValuesForRequest(t, storageURL, map[string]string{xhttp.AmzStorageClass: "HEADER"})
+	if got := resolvedConditionValues(storageValues, strings.ToLower(xhttp.AmzStorageClass)); !slices.Equal(got, []string{"HEADER"}) {
+		t.Errorf("storage class did not use header precedence: %v", got)
+	}
+
+	fromQuery := condValuesForRequest(t,
+		"http://minio.local/bkt/obj?"+url.Values{xhttp.AmzObjectLockMode: {"COMPLIANCE"}}.Encode(), nil)
+	if got := resolvedConditionValues(fromQuery, "object-lock-mode"); len(got) != 0 {
+		t.Errorf("object-lock query value reached header condition as %v", got)
+	}
+}
+
+func TestGetConditionValuesUsesEffectiveRequestTags(t *testing.T) {
+	rawURL := "http://minio.local/bkt/obj?" + url.Values{
+		strings.ToLower(xhttp.AmzObjectTagging): {"security=public&virus=true"},
+	}.Encode()
+
+	// Generic operations such as CopyObject must not gain RequestObjectTag
+	// values from a query parameter they do not consume.
+	withoutEffectiveTags := condValuesForRequest(t, rawURL, nil)
+	if len(withoutEffectiveTags["RequestObjectTag/security"]) != 0 || len(withoutEffectiveTags["RequestObjectTagKeys"]) != 0 {
+		t.Fatalf("query tags leaked into a generic operation: %v", withoutEffectiveTags)
+	}
+
+	effectiveTags := "security=public&virus=true"
+	withEffectiveTags := condValuesForRequestWithTags(t, rawURL, nil, "", &effectiveTags)
+	if !slices.Equal(withEffectiveTags["RequestObjectTag/security"], []string{"public"}) {
+		t.Fatalf("effective request tag missing: %v", withEffectiveTags)
+	}
+	if !slices.Contains(withEffectiveTags["RequestObjectTagKeys"], "security") ||
+		!slices.Contains(withEffectiveTags["RequestObjectTagKeys"], "virus") {
+		t.Fatalf("effective request tag keys missing: %v", withEffectiveTags["RequestObjectTagKeys"])
+	}
+
+	security, err := condition.NewStringEqualsFunc("", condition.NewKey(condition.RequestObjectTag, "security"), "public")
+	if err != nil {
+		t.Fatal(err)
+	}
+	allowedKeys, err := condition.NewStringLikeFunc("ForAllValues", condition.RequestObjectTagKeys.ToKey(), "security", "virus")
+	if err != nil {
+		t.Fatal(err)
+	}
+	conditions := condition.NewFunctions(security, allowedKeys)
+	if conditions.Evaluate(withoutEffectiveTags) {
+		t.Fatal("query upload satisfied request-tag policy without effective tags")
+	}
+	if !conditions.Evaluate(withEffectiveTags) {
+		t.Fatal("effective query tags did not satisfy request-tag policy")
+	}
+}
+
+func TestBucketPolicySSEConditionUsesHeader(t *testing.T) {
+	fn, err := condition.NewStringEqualsFunc("", condition.S3XAmzServerSideEncryption.ToKey(), "aws:kms")
+	if err != nil {
+		t.Fatal(err)
+	}
+	conditions := condition.NewFunctions(fn)
+	if conditions.Evaluate(condValuesForRequest(t,
+		"http://minio.local/bkt/obj?x-amz-server-side-encryption=aws%3Akms", nil)) {
+		t.Error("query parameter satisfied a condition on the SSE request header")
+	}
+	if !conditions.Evaluate(condValuesForRequest(t, "http://minio.local/bkt/obj",
+		map[string]string{xhttp.AmzServerSideEncryption: "aws:kms"})) {
+		t.Error("SSE request header did not satisfy its condition")
+	}
+}
+
+// The end to end shape of the bypass: an IpAddress condition restricting a
+// bucket to an internal range, against a request from outside it.
+func TestBucketPolicySourceIPCannotBeForged(t *testing.T) {
+	_, cidr, err := net.ParseCIDR("10.0.0.0/8")
+	if err != nil {
+		t.Fatal(err)
+	}
+	fn, err := condition.NewIPAddressFunc(condition.AWSSourceIP.ToKey(), cidr)
+	if err != nil {
+		t.Fatal(err)
+	}
+	bp := policy.BucketPolicy{
+		Version: policy.DefaultVersion,
+		Statements: []policy.BPStatement{{
+			Effect:     policy.Allow,
+			Principal:  policy.NewPrincipal("*"),
+			Actions:    policy.NewActionSet(policy.GetObjectAction),
+			Resources:  policy.NewResourceSet(policy.NewResource("bkt/*")),
+			Conditions: condition.NewFunctions(fn),
+		}},
+	}
+	allowed := func(rawURL string, header map[string]string) bool {
+		return bp.IsAllowed(policy.BucketPolicyArgs{
+			Action:          policy.GetObjectAction,
+			BucketName:      "bkt",
+			ObjectName:      "obj",
+			ConditionValues: condValuesForRequest(t, rawURL, header),
+		})
+	}
+
+	if allowed("http://minio.local/bkt/obj", nil) {
+		t.Fatal("baseline: an address outside 10.0.0.0/8 must not satisfy the condition")
+	}
+	if allowed("http://minio.local/bkt/obj?SourceIp=10.1.2.3", nil) {
+		t.Error("a query parameter forged aws:SourceIp")
+	}
+	if allowed("http://minio.local/bkt/obj", map[string]string{"Sourceip": "10.1.2.3"}) {
+		t.Error("a header forged aws:SourceIp")
+	}
+}
+
+// "Deny unless the connection is TLS" is the usual hardening statement, and
+// aws:SecureTransport is computed from r.TLS.
+func TestBucketPolicySecureTransportCannotBeForged(t *testing.T) {
+	fn, err := condition.NewBoolFunc(condition.AWSSecureTransport.ToKey(), false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	bp := policy.BucketPolicy{
+		Version: policy.DefaultVersion,
+		Statements: []policy.BPStatement{
+			{
+				Effect: policy.Allow, Principal: policy.NewPrincipal("*"),
+				Actions:   policy.NewActionSet(policy.GetObjectAction),
+				Resources: policy.NewResourceSet(policy.NewResource("bkt/*")),
+			},
+			{
+				Effect: policy.Deny, Principal: policy.NewPrincipal("*"),
+				Actions:    policy.NewActionSet(policy.GetObjectAction),
+				Resources:  policy.NewResourceSet(policy.NewResource("bkt/*")),
+				Conditions: condition.NewFunctions(fn),
+			},
+		},
+	}
+	allowed := func(rawURL string, header map[string]string) bool {
+		return bp.IsAllowed(policy.BucketPolicyArgs{
+			Action:          policy.GetObjectAction,
+			BucketName:      "bkt",
+			ObjectName:      "obj",
+			ConditionValues: condValuesForRequest(t, rawURL, header),
+		})
+	}
+
+	// r.TLS is nil throughout, so every one of these is a plaintext request.
+	if allowed("http://minio.local/bkt/obj", nil) {
+		t.Fatal("baseline: a plaintext request must be denied")
+	}
+	if allowed("http://minio.local/bkt/obj?SecureTransport=true", nil) {
+		t.Error("a query parameter forged aws:SecureTransport")
+	}
+	if allowed("http://minio.local/bkt/obj", map[string]string{"Securetransport": "true"}) {
+		t.Error("a header forged aws:SecureTransport")
+	}
+}
+
+// Reserving the server's own keys must not stop the request from supplying the
+// values that are client-derived by design.
+func TestGetConditionValuesKeepsClientDerivedKeys(t *testing.T) {
+	got := condValuesForRequest(t, "http://minio.local/bkt/obj?prefix=team%2F",
+		map[string]string{
+			xhttp.AmzObjectLockMode:       "GOVERNANCE",
+			xhttp.AmzServerSideEncryption: "aws:kms",
+			"X-Amz-Meta-Team":             "storage",
+			xhttp.AmzObjectTagging:        "project=silo",
+		})
+
+	for _, tc := range []struct {
+		key  string
+		want string
+	}{
+		{"Object-Lock-Mode", "GOVERNANCE"},
+		{xhttp.AmzServerSideEncryption, "aws:kms"},
+		{"X-Amz-Meta-Team", "storage"},
+		{"RequestObjectTag/project", "silo"},
+		{"prefix", "team/"},
+	} {
+		if !slices.Contains(got[tc.key], tc.want) {
+			t.Errorf("%s: expected %q, got %v", tc.key, tc.want, got[tc.key])
+		}
+	}
+	if !slices.Contains(got["RequestObjectTagKeys"], "project") {
+		t.Errorf("RequestObjectTagKeys: expected project, got %v", got["RequestObjectTagKeys"])
+	}
+
+	if len(got["ExistingObjectTag/project"]) != 0 {
+		t.Errorf("request tags leaked into ExistingObjectTag: %v", got["ExistingObjectTag/project"])
+	}
+}
+
+func TestGetConditionValuesSeparatesRequestAndExistingTags(t *testing.T) {
+	got := condValuesForRequestWithExistingTags(t, "http://minio.local/bkt/obj",
+		map[string]string{xhttp.AmzObjectTagging: "project=request&new=yes"},
+		"project=stored&old=yes")
+
+	for _, tc := range []struct {
+		key  string
+		want string
+	}{
+		{"RequestObjectTag/project", "request"},
+		{"RequestObjectTag/new", "yes"},
+		{"ExistingObjectTag/project", "stored"},
+		{"ExistingObjectTag/old", "yes"},
+	} {
+		if !slices.Equal(got[tc.key], []string{tc.want}) {
+			t.Errorf("%s: expected %q, got %v", tc.key, tc.want, got[tc.key])
+		}
+	}
+	if len(got["ExistingObjectTag/new"]) != 0 || len(got["RequestObjectTag/old"]) != 0 {
+		t.Errorf("tag sources crossed: request new=%v, existing old=%v",
+			got["ExistingObjectTag/new"], got["RequestObjectTag/old"])
+	}
+}
+
+// Keys the server did not populate for this request are as forgeable as ones it
+// did, so the reservation cannot depend on presence.
+func TestGetConditionValuesRejectsAbsentInternalKeys(t *testing.T) {
+	for _, key := range []string{
+		"signatureAge",
+		"groups",
+		"DurationSeconds",
+		"ExistingObjectTag/security",
+		"RequestObjectTag/security",
+		"RequestObjectTagKeys",
+		"object-lock-mode",
+		"object-lock-remaining-retention-days",
+	} {
+		t.Run(key, func(t *testing.T) {
+			got := condValuesForRequest(t,
+				"http://minio.local/bkt/obj?"+url.Values{key: {"ATTACKER"}}.Encode(), nil)
+			if slices.Contains(got[key], "ATTACKER") {
+				t.Errorf("?%s= was accepted into the condition values as %v", key, got[key])
+			}
+		})
+	}
+}
+
+func TestGetConditionValuesOnlyAcceptsPresignedSignatureAge(t *testing.T) {
+	const signatureAgeHeader = "x-amz-signature-age"
+
+	for _, tc := range []struct {
+		name    string
+		target  string
+		headers map[string]string
+		want    bool
+	}{
+		{
+			name:    "anonymous client header",
+			target:  "http://minio.local/bkt/obj",
+			headers: map[string]string{signatureAgeHeader: "1"},
+		},
+		{
+			name:   "header-signed client header",
+			target: "http://minio.local/bkt/obj",
+			headers: map[string]string{
+				xhttp.Authorization: signV4Algorithm + " attacker",
+				signatureAgeHeader:  "1",
+			},
+		},
+		{
+			name: "presigned verifier value",
+			target: "http://minio.local/bkt/obj?" + url.Values{
+				xhttp.AmzCredential: {"access/20260803/us-east-1/s3/aws4_request"},
+			}.Encode(),
+			headers: map[string]string{signatureAgeHeader: "250"},
+			want:    true,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			got := condValuesForRequest(t, tc.target, tc.headers)
+			_, ok := got["signatureAge"]
+			if ok != tc.want {
+				t.Fatalf("signatureAge presence: expected %v, got %v", tc.want, got["signatureAge"])
+			}
+		})
+	}
+}
+
+// The object-lock value is stored under the header spelling while the policy key
+// that reads it is lower case. Reserving only one spelling lets the other be
+// supplied and resolved in its place - which the policy package's exact-name
+// lookup then prefers over the real one.
+func TestGetConditionValuesObjectLockSpelling(t *testing.T) {
+	got := condValuesForRequest(t,
+		"http://minio.local/bkt/obj?object-lock-mode=COMPLIANCE",
+		map[string]string{xhttp.AmzObjectLockMode: "GOVERNANCE"})
+
+	if v, ok := got["object-lock-mode"]; ok {
+		t.Errorf("the lower-case spelling was accepted: %v", v)
+	}
+	if !slices.Equal(got["Object-Lock-Mode"], []string{"GOVERNANCE"}) {
+		t.Errorf("expected the header value to stand, got %v", got["Object-Lock-Mode"])
+	}
+
+	fn, err := condition.NewStringEqualsFunc("",
+		condition.S3ObjectLockMode.ToKey(), "COMPLIANCE")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if condition.NewFunctions(fn).Evaluate(got) {
+		t.Error("a policy requiring COMPLIANCE was satisfied by a GOVERNANCE request")
+	}
+}
+
+// Resource variables read the condition map directly, so a forgeable key is a
+// forgeable resource path. ${ldap:user} and ${jwt:preferred_username} are the
+// home-directory idiom for LDAP and OIDC deployments; the server derives them
+// from the credential, and a request must not be able to answer them.
+func TestBucketPolicyResourceVariableCannotBeForged(t *testing.T) {
+	for _, tc := range []struct{ variable, param, value string }{
+		{"${ldap:user}", "user", "alice"},
+		{"${ldap:username}", "username", "alice"},
+		{"${jwt:preferred_username}", "preferred_username", "alice"},
+		{"${jwt:sub}", "sub", "alice"},
+		{"${aws:username}", "username", "alice"},
+	} {
+		t.Run(tc.variable, func(t *testing.T) {
+			bp := policy.BucketPolicy{Version: policy.DefaultVersion, Statements: []policy.BPStatement{{
+				Effect:    policy.Allow,
+				Principal: policy.NewPrincipal("*"),
+				Actions:   policy.NewActionSet(policy.GetObjectAction),
+				Resources: policy.NewResourceSet(policy.NewResource("bkt/" + tc.variable + "/*")),
+			}}}
+			args := policy.BucketPolicyArgs{
+				Action: policy.GetObjectAction, BucketName: "bkt", ObjectName: tc.value + "/secret",
+			}
+			args.ConditionValues = condValuesForRequest(t,
+				"http://minio.local/bkt/"+tc.value+"/secret?"+
+					url.Values{tc.param: {tc.value}}.Encode(), nil)
+			if bp.IsAllowed(args) {
+				t.Errorf("?%s=%s expanded %s and granted the prefix", tc.param, tc.value, tc.variable)
+			}
+		})
+	}
+}
diff --git a/cmd/handler-utils.go b/cmd/handler-utils.go
index 7e70d5cb2..ad087dcf4 100644
--- a/cmd/handler-utils.go
+++ b/cmd/handler-utils.go
@@ -142,7 +142,62 @@ var userMetadataKeyPrefixes = []string{
 
 // extractMetadataFromReq extracts metadata from HTTP header and HTTP queryString.
 func extractMetadataFromReq(ctx context.Context, r *http.Request) (metadata map[string]string, err error) {
-	return extractMetadata(ctx, textproto.MIMEHeader(r.Form), textproto.MIMEHeader(r.Header))
+	metadata, err = extractMetadata(ctx, textproto.MIMEHeader(r.Form), textproto.MIMEHeader(r.Header))
+	if err != nil {
+		return nil, err
+	}
+
+	// Keep the metadata consumed by object operations in lock-step with policy
+	// conditions: an explicitly present header wins, otherwise use the query
+	// value accepted by the existing S3-compatible request path.
+	for _, name := range []string{xhttp.AmzStorageClass, xhttp.AmzObjectTagging} {
+		if value, ok := getRequestHeaderOrQueryValue(r, name); ok {
+			metadata[name] = value
+		}
+	}
+	return metadata, nil
+}
+
+// getRequestHeaderOrQueryValue returns the effective value of a request field.
+// Header presence takes precedence even when its value is empty. Query lookup
+// remains case-insensitive for compatibility with extractMetadataFromReq.
+func getRequestHeaderOrQueryValue(r *http.Request, name string) (string, bool) {
+	if values, ok := getRequestValues(r.Header, name, http.CanonicalHeaderKey(name)); ok {
+		return strings.Join(values, ","), true
+	}
+	if values, ok := getRequestValues(http.Header(r.Form), name, strings.ToLower(name)); ok {
+		return strings.Join(values, ","), true
+	}
+	return "", false
+}
+
+func getRequestValues(values http.Header, name, preferred string) ([]string, bool) {
+	if value, ok := values[preferred]; ok {
+		return value, true
+	}
+
+	canonical, lower := http.CanonicalHeaderKey(name), strings.ToLower(name)
+	for _, key := range []string{canonical, lower} {
+		if key == preferred {
+			continue
+		}
+		if value, ok := values[key]; ok {
+			return value, true
+		}
+	}
+
+	// Multiple differently-cased spellings are malformed but were previously
+	// accepted. Pick one deterministically instead of depending on map order.
+	match := ""
+	for key := range values {
+		if strings.EqualFold(key, name) && (match == "" || key < match) {
+			match = key
+		}
+	}
+	if match != "" {
+		return values[match], true
+	}
+	return nil, false
 }
 
 func extractMetadata(ctx context.Context, mimesHeader ...textproto.MIMEHeader) (metadata map[string]string, err error) {
diff --git a/cmd/handler-utils_test.go b/cmd/handler-utils_test.go
index f6691d329..6a7bcd611 100644
--- a/cmd/handler-utils_test.go
+++ b/cmd/handler-utils_test.go
@@ -27,6 +27,7 @@ import (
 	"net/url"
 	"os"
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/minio/minio/internal/config"
@@ -194,6 +195,63 @@ func TestExtractMetadataHeaders(t *testing.T) {
 	}
 }
 
+func TestExtractMetadataFromRequestUsesHeaderPrecedence(t *testing.T) {
+	query := make(url.Values)
+	query.Set(strings.ToLower(xhttp.AmzStorageClass), "QUERY-CLASS")
+	query.Set(strings.ToLower(xhttp.AmzObjectTagging), "source=query")
+	req, err := http.NewRequest(http.MethodGet, "http://localhost/test?"+query.Encode(), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req.Header.Set(xhttp.AmzStorageClass, "HEADER-CLASS")
+	req.Header.Set(xhttp.AmzObjectTagging, "source=header")
+	if err = req.ParseForm(); err != nil {
+		t.Fatal(err)
+	}
+
+	metadata, err := extractMetadataFromReq(t.Context(), req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := metadata[xhttp.AmzStorageClass]; got != "HEADER-CLASS" {
+		t.Fatalf("storage class: expected header, got %q", got)
+	}
+	if got := metadata[xhttp.AmzObjectTagging]; got != "source=header" {
+		t.Fatalf("tagging: expected header, got %q", got)
+	}
+
+	// Presence, rather than a non-empty value, establishes precedence. This
+	// prevents a query value from taking over when a signed header is empty.
+	req.Header[xhttp.AmzObjectTagging] = []string{""}
+	if got, ok := getRequestHeaderOrQueryValue(req, xhttp.AmzObjectTagging); !ok || got != "" {
+		t.Fatalf("empty header did not override query: value=%q present=%v", got, ok)
+	}
+}
+
+func TestExtractMetadataFromRequestKeepsQueryCompatibility(t *testing.T) {
+	query := make(url.Values)
+	query.Set(strings.ToLower(xhttp.AmzStorageClass), "REDUCED_REDUNDANCY")
+	query.Set(strings.ToLower(xhttp.AmzObjectTagging), "security=public")
+	req, err := http.NewRequest(http.MethodGet, "http://localhost/test?"+query.Encode(), nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = req.ParseForm(); err != nil {
+		t.Fatal(err)
+	}
+
+	metadata, err := extractMetadataFromReq(t.Context(), req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := metadata[xhttp.AmzStorageClass]; got != "REDUCED_REDUNDANCY" {
+		t.Fatalf("storage class query value lost: %q", got)
+	}
+	if got := metadata[xhttp.AmzObjectTagging]; got != "security=public" {
+		t.Fatalf("tagging query value lost: %q", got)
+	}
+}
+
 func TestExtractReplicationMetadataHeaders(t *testing.T) {
 	header := http.Header{
 		"X-Minio-Replication-Server-Side-Encryption-Sealed-Key":     []string{"sealed-key"},
diff --git a/cmd/object-handlers.go b/cmd/object-handlers.go
index 7b04337bf..296817ed5 100644
--- a/cmd/object-handlers.go
+++ b/cmd/object-handlers.go
@@ -387,11 +387,7 @@ func (api objectAPIHandlers) getObjectHandler(ctx context.Context, objectAPI Obj
 			return true
 		}
 
-		if oi.UserTags != "" {
-			r.Header.Set(xhttp.AmzObjectTagging, oi.UserTags)
-		}
-
-		if s3Error := authorizeRequest(ctx, r, policy.GetObjectAction); s3Error != ErrNone {
+		if s3Error := authorizeRequestWithExistingTags(ctx, r, policy.GetObjectAction, oi.UserTags); s3Error != ErrNone {
 			writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
 			return true
 		}
@@ -429,15 +425,17 @@ func (api objectAPIHandlers) getObjectHandler(ctx context.Context, objectAPI Obj
 			}
 		}
 		if reader == nil || !proxy.Proxy {
+			// The conditional callback has already written 304/412. Do not
+			// authorize again without the stored tags or write a second response.
+			if isErrPreconditionFailed(err) {
+				return
+			}
 			// validate if the request indeed was authorized, if it wasn't we need to return "ErrAccessDenied"
 			// instead of any namespace related error.
 			if s3Error := authorizeRequest(ctx, r, policy.GetObjectAction); s3Error != ErrNone {
 				writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
 				return
 			}
-			if isErrPreconditionFailed(err) {
-				return
-			}
 			if proxy.Err != nil {
 				writeErrorResponse(ctx, w, toAPIError(ctx, proxy.Err), r.URL)
 				return
@@ -839,12 +837,7 @@ func (api objectAPIHandlers) headObjectHandler(ctx context.Context, objectAPI Ob
 		}
 	}
 
-	if objInfo.UserTags != "" {
-		// Set this such that authorization policies can be applied on the object tags.
-		r.Header.Set(xhttp.AmzObjectTagging, objInfo.UserTags)
-	}
-
-	if s3Error := authorizeRequest(ctx, r, policy.GetObjectAction); s3Error != ErrNone {
+	if s3Error := authorizeRequestWithExistingTags(ctx, r, policy.GetObjectAction, objInfo.UserTags); s3Error != ErrNone {
 		writeErrorResponseHeadersOnly(w, errorCodes.ToAPIErr(s3Error))
 		return
 	}
@@ -1055,10 +1048,7 @@ func getCpObjMetadataFromHeader(ctx context.Context, r *http.Request, userMeta m
 	// Storage class is special, it can be replaced regardless of the
 	// metadata directive, if set should be preserved and replaced
 	// to the destination metadata.
-	sc := r.Header.Get(xhttp.AmzStorageClass)
-	if sc == "" {
-		sc = r.Form.Get(xhttp.AmzStorageClass)
-	}
+	sc, _ := getRequestHeaderOrQueryValue(r, xhttp.AmzStorageClass)
 
 	// if x-amz-metadata-directive says REPLACE then
 	// we extract metadata from the input headers.
@@ -1256,9 +1246,10 @@ func (api objectAPIHandlers) CopyObjectHandler(w http.ResponseWriter, r *http.Re
 		return
 	}
 
-	// Validate storage class metadata if present
-	dstSc := r.Header.Get(xhttp.AmzStorageClass)
-	if dstSc != "" && !storageclass.IsValid(dstSc) {
+	// Validate the storage class header if present. Query values retain the
+	// existing compatibility path, including its historical validation behavior.
+	dstSc, _ := getRequestHeaderOrQueryValue(r, xhttp.AmzStorageClass)
+	if headerStorageClass := r.Header.Get(xhttp.AmzStorageClass); headerStorageClass != "" && !storageclass.IsValid(headerStorageClass) {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidStorageClass), r.URL)
 		return
 	}
@@ -1857,7 +1848,8 @@ func (api objectAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Req
 		return
 	}
 
-	// Validate storage class metadata if present
+	// Validate the storage class header if present. Query values retain the
+	// existing compatibility path, including its historical validation behavior.
 	if sc := r.Header.Get(xhttp.AmzStorageClass); sc != "" {
 		if !storageclass.IsValid(sc) {
 			writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidStorageClass), r.URL)
@@ -1906,13 +1898,11 @@ func (api objectAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Req
 		return
 	}
 
-	if objTags := r.Header.Get(xhttp.AmzObjectTagging); objTags != "" {
+	if objTags := metadata[xhttp.AmzObjectTagging]; objTags != "" {
 		if _, err := tags.ParseObjectTags(objTags); err != nil {
 			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
 			return
 		}
-
-		metadata[xhttp.AmzObjectTagging] = objTags
 	}
 
 	var (
@@ -1924,7 +1914,12 @@ func (api objectAPIHandlers) PutObjectHandler(w http.ResponseWriter, r *http.Req
 	)
 
 	// Check if put is allowed
-	if s3Err = isPutActionAllowed(ctx, rAuthType, bucket, object, r, policy.PutObjectAction); s3Err != ErrNone {
+	requestTags, hasRequestTags := metadata[xhttp.AmzObjectTagging]
+	var requestTagsPtr *string
+	if hasRequestTags {
+		requestTagsPtr = &requestTags
+	}
+	if s3Err = isPutActionAllowedWithRequestTags(ctx, rAuthType, bucket, object, r, policy.PutObjectAction, requestTagsPtr); s3Err != ErrNone {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Err), r.URL)
 		return
 	}
@@ -2271,13 +2266,12 @@ func (api objectAPIHandlers) PutObjectExtractHandler(w http.ResponseWriter, r *h
 		return
 	}
 
-	// Validate storage class metadata if present
-	sc := r.Header.Get(xhttp.AmzStorageClass)
-	if sc != "" {
-		if !storageclass.IsValid(sc) {
-			writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidStorageClass), r.URL)
-			return
-		}
+	// Validate the storage class header if present. PutObjectExtract now also
+	// consumes the compatible query value so policy and operation stay aligned.
+	sc, _ := getRequestHeaderOrQueryValue(r, xhttp.AmzStorageClass)
+	if headerStorageClass := r.Header.Get(xhttp.AmzStorageClass); headerStorageClass != "" && !storageclass.IsValid(headerStorageClass) {
+		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidStorageClass), r.URL)
+		return
 	}
 
 	clientETag, err := etag.FromContentMD5(r.Header)
@@ -3205,12 +3199,7 @@ func (api objectAPIHandlers) GetObjectTaggingHandler(w http.ResponseWriter, r *h
 		}
 	}
 
-	// Set this such that authorization policies can be applied on the object tags.
-	if tags := ot.String(); tags != "" {
-		r.Header.Set(xhttp.AmzObjectTagging, tags)
-	}
-
-	if s3Error := authorizeRequest(ctx, r, policy.GetObjectTaggingAction); s3Error != ErrNone {
+	if s3Error := authorizeRequestWithExistingTags(ctx, r, policy.GetObjectTaggingAction, ot.String()); s3Error != ErrNone {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
 		return
 	}
@@ -3264,12 +3253,14 @@ func (api objectAPIHandlers) PutObjectTaggingHandler(w http.ResponseWriter, r *h
 		writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
 		return
 	}
+	tagsStr := tags.String()
 
 	// Set this such that authorization policies can be applied on the object tags.
-	r.Header.Set(xhttp.AmzObjectTagging, tags.String())
+	r.Header.Set(xhttp.AmzObjectTagging, tagsStr)
 
-	// Allow putObjectTagging if policy action is set
-	if s3Error := checkRequestAuthType(ctx, r, policy.PutObjectTaggingAction, bucket, object); s3Error != ErrNone {
+	logger.GetReqInfo(ctx).BucketName = bucket
+	logger.GetReqInfo(ctx).ObjectName = object
+	if s3Error := authenticateRequest(ctx, r, policy.PutObjectTaggingAction); s3Error != ErrNone {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
 		return
 	}
@@ -3281,6 +3272,14 @@ func (api objectAPIHandlers) PutObjectTaggingHandler(w http.ResponseWriter, r *h
 	}
 
 	objInfo, err := objAPI.GetObjectInfo(ctx, bucket, object, opts)
+	existingTags := ""
+	if err == nil {
+		existingTags = objInfo.UserTags
+	}
+	if s3Error := authorizeRequestWithExistingTags(ctx, r, policy.PutObjectTaggingAction, existingTags); s3Error != ErrNone {
+		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
+		return
+	}
 	if err != nil {
 		// if object is not found locally, but exists on peer site - proxy
 		// the tagging request to peer site. The response to client will
@@ -3314,7 +3313,6 @@ func (api objectAPIHandlers) PutObjectTaggingHandler(w http.ResponseWriter, r *h
 		writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
 		return
 	}
-	tagsStr := tags.String()
 
 	dsc := mustReplicate(ctx, bucket, object, getMustReplicateOptions(objInfo.UserDefined, tagsStr, objInfo.ReplicationStatus, replication.MetadataReplicationType, opts))
 	if dsc.ReplicateAny() {
@@ -3413,13 +3411,8 @@ func (api objectAPIHandlers) DeleteObjectTaggingHandler(w http.ResponseWriter, r
 		return
 	}
 
-	if userTags := oi.UserTags; userTags != "" {
-		// Set this such that authorization policies can be applied on the object tags.
-		r.Header.Set(xhttp.AmzObjectTagging, oi.UserTags)
-	}
-
 	// Allow deleteObjectTagging if policy action is set
-	if s3Error := checkRequestAuthType(ctx, r, policy.DeleteObjectTaggingAction, bucket, object); s3Error != ErrNone {
+	if s3Error := checkRequestAuthTypeWithExistingTags(ctx, r, policy.DeleteObjectTaggingAction, bucket, object, oi.UserTags); s3Error != ErrNone {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
 		return
 	}
diff --git a/cmd/object-multipart-handlers.go b/cmd/object-multipart-handlers.go
index 048bf7076..fcc6d5b64 100644
--- a/cmd/object-multipart-handlers.go
+++ b/cmd/object-multipart-handlers.go
@@ -80,7 +80,12 @@ func (api objectAPIHandlers) NewMultipartUploadHandler(w http.ResponseWriter, r
 		return
 	}
 
-	if s3Error := checkRequestAuthType(ctx, r, policy.PutObjectAction, bucket, object); s3Error != ErrNone {
+	requestTags, hasRequestTags := getRequestHeaderOrQueryValue(r, xhttp.AmzObjectTagging)
+	var requestTagsPtr *string
+	if hasRequestTags {
+		requestTagsPtr = &requestTags
+	}
+	if s3Error := checkRequestAuthTypeWithRequestTags(ctx, r, policy.PutObjectAction, bucket, object, requestTagsPtr); s3Error != ErrNone {
 		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(s3Error), r.URL)
 		return
 	}
@@ -91,7 +96,8 @@ func (api objectAPIHandlers) NewMultipartUploadHandler(w http.ResponseWriter, r
 		AutoEncrypt: globalAutoEncryption,
 	})
 
-	// Validate storage class metadata if present
+	// Validate the storage class header if present. Query values retain the
+	// existing compatibility path, including its historical validation behavior.
 	if sc := r.Header.Get(xhttp.AmzStorageClass); sc != "" {
 		if !storageclass.IsValid(sc) {
 			writeErrorResponse(ctx, w, errorCodes.ToAPIErr(ErrInvalidStorageClass), r.URL)
@@ -148,13 +154,11 @@ func (api objectAPIHandlers) NewMultipartUploadHandler(w http.ResponseWriter, r
 		return
 	}
 
-	if objTags := r.Header.Get(xhttp.AmzObjectTagging); objTags != "" {
+	if objTags := metadata[xhttp.AmzObjectTagging]; objTags != "" {
 		if _, err := tags.ParseObjectTags(objTags); err != nil {
 			writeErrorResponse(ctx, w, toAPIError(ctx, err), r.URL)
 			return
 		}
-
-		metadata[xhttp.AmzObjectTagging] = objTags
 	}
 	if r.Header.Get(xhttp.AmzBucketReplicationStatus) == replication.Replica.String() {
 		if s3Err := isPutActionAllowed(ctx, getRequestAuthType(r), bucket, object, r, policy.ReplicateObjectAction); s3Err != ErrNone {
@@ -968,7 +972,7 @@ func (api objectAPIHandlers) CompleteMultipartUploadHandler(w http.ResponseWrite
 
 	// The parts list must be strictly increasing by part number. Gaps are
 	// allowed, repeats are not - sort.SliceIsSorted() with a '<' predicate
-	// considers equal neighbours sorted, so it is checked explicitly here,
+	// considers equal neighbors sorted, so it is checked explicitly here,
 	// before anything is assembled into the target object.
 	for i := 1; i < len(complMultipartUpload.Parts); i++ {
 		if complMultipartUpload.Parts[i-1].PartNumber >= complMultipartUpload.Parts[i].PartNumber {
diff --git a/cmd/object-multipart-handlers_test.go b/cmd/object-multipart-handlers_test.go
index 79189b92e..87bd2ef14 100644
--- a/cmd/object-multipart-handlers_test.go
+++ b/cmd/object-multipart-handlers_test.go
@@ -68,7 +68,7 @@ func testAPICompleteMultipartHandlerPartOrder(obj ObjectLayer, instanceType, buc
 	}{
 		// Defect reproduction. A duplicated part number is the case that
 		// sort.SliceIsSorted() used to accept, because its '<' predicate treats
-		// equal neighbours as sorted. Each of these assembled the same part into
+		// equal neighbors as sorted. Each of these assembled the same part into
 		// the object more than once, inflating it past what was uploaded.
 		{
 			name:               "duplicate-part",
diff --git a/cmd/sts-handlers_test.go b/cmd/sts-handlers_test.go
index f4aa65981..24882745a 100644
--- a/cmd/sts-handlers_test.go
+++ b/cmd/sts-handlers_test.go
@@ -41,6 +41,8 @@ import (
 	"github.com/minio/minio-go/v7"
 	cr "github.com/minio/minio-go/v7/pkg/credentials"
 	"github.com/minio/minio-go/v7/pkg/set"
+	"github.com/minio/minio-go/v7/pkg/tags"
+	xhttp "github.com/minio/minio/internal/http"
 	"github.com/minio/pkg/v3/ldap"
 )
 
@@ -417,6 +419,15 @@ func (s *TestSuiteIAM) TestSTSWithTags(c *check) {
       "Resource":    "arn:aws:s3:::%s/*",
       "Condition": {  "StringEquals": {"s3:ExistingObjectTag/security": "public" } }
     },
+    {
+      "Effect":     "Allow",
+      "Action":     "s3:PutObjectTagging",
+      "Resource":    "arn:aws:s3:::%s/*",
+      "Condition": { "StringEquals": {
+        "s3:ExistingObjectTag/virus": "true",
+        "s3:RequestObjectTag/security": "public"
+      } }
+    },
     {
       "Effect":     "Allow",
       "Action":     "s3:DeleteObject",
@@ -431,6 +442,9 @@ func (s *TestSuiteIAM) TestSTSWithTags(c *check) {
         "arn:aws:s3:::%s/*"
       ],
       "Condition": {
+        "StringEquals": {
+          "s3:RequestObjectTag/security": "public"
+        },
         "ForAllValues:StringLike": {
           "s3:RequestObjectTagKeys": [
             "security",
@@ -440,7 +454,7 @@ func (s *TestSuiteIAM) TestSTSWithTags(c *check) {
       }
     }
   ]
-}`, bucket, bucket, bucket, bucket)
+}`, bucket, bucket, bucket, bucket, bucket)
 	err = s.adm.AddCannedPolicy(ctx, policy, policyBytes)
 	if err != nil {
 		c.Fatalf("policy add error: %v", err)
@@ -462,8 +476,108 @@ func (s *TestSuiteIAM) TestSTSWithTags(c *check) {
 
 	// confirm that the user is able to access the bucket
 	uClient := s.getUserClient(c, accessKey, secretKey, "")
+	queryObject := object + "-query-tags"
+	queryTags := "security=public&virus=true"
+	// Query storage-class values were historically accepted without the strict
+	// header validation. Pin that compatibility while proving they are consumed.
+	presignedPut, err := uClient.Presign(ctx, http.MethodPut, bucket, queryObject, time.Minute, url.Values{
+		"x-amz-storage-class": {"CUSTOM_COMPAT"},
+		"x-amz-tagging":       {queryTags},
+	})
+	if err != nil {
+		c.Fatalf("unable to presign query-tagged upload: %v", err)
+	}
+	putReq, err := http.NewRequestWithContext(ctx, http.MethodPut, presignedPut.String(), bytes.NewReader([]byte("stuff")))
+	if err != nil {
+		c.Fatalf("unable to build query-tagged upload: %v", err)
+	}
+	putResp, err := s.TestSuiteCommon.client.Do(putReq)
+	if err != nil {
+		c.Fatalf("query-tagged upload failed: %v", err)
+	}
+	putBody, readErr := io.ReadAll(putResp.Body)
+	putResp.Body.Close()
+	if readErr != nil {
+		c.Fatalf("unable to read query-tagged upload response: %v", readErr)
+	}
+	if putResp.StatusCode != http.StatusOK {
+		c.Fatalf("query-tagged upload returned %s: %s", putResp.Status, putBody)
+	}
+	storedTags, err := s.client.GetObjectTagging(ctx, bucket, queryObject, minio.GetObjectTaggingOptions{})
+	if err != nil {
+		c.Fatalf("unable to read persisted query tags: %v", err)
+	}
+	if got := storedTags.ToMap(); got["security"] != "public" || got["virus"] != "true" {
+		c.Fatalf("query tags were not persisted: %v", got)
+	}
+	queryObjectInfo, err := s.testServer.Obj.GetObjectInfo(ctx, bucket, queryObject, ObjectOptions{})
+	if err != nil {
+		c.Fatalf("unable to inspect query-tagged object: %v", err)
+	}
+	if queryObjectInfo.StorageClass != "CUSTOM_COMPAT" {
+		c.Fatalf("query storage class was not persisted: %q", queryObjectInfo.StorageClass)
+	}
+	c.mustGetObject(ctx, uClient, bucket, queryObject)
+
+	multipartObject := object + "-multipart-query-tags"
+	presignedMultipart, err := uClient.Presign(ctx, http.MethodPost, bucket, multipartObject, time.Minute, url.Values{
+		"uploads":       {""},
+		"x-amz-tagging": {queryTags},
+	})
+	if err != nil {
+		c.Fatalf("unable to presign query-tagged multipart upload: %v", err)
+	}
+	multipartReq, err := http.NewRequestWithContext(ctx, http.MethodPost, presignedMultipart.String(), nil)
+	if err != nil {
+		c.Fatalf("unable to build query-tagged multipart upload: %v", err)
+	}
+	multipartResp, err := s.TestSuiteCommon.client.Do(multipartReq)
+	if err != nil {
+		c.Fatalf("query-tagged multipart upload failed: %v", err)
+	}
+	multipartBody, readErr := io.ReadAll(multipartResp.Body)
+	multipartResp.Body.Close()
+	if readErr != nil {
+		c.Fatalf("unable to read query-tagged multipart response: %v", readErr)
+	}
+	if multipartResp.StatusCode != http.StatusOK {
+		c.Fatalf("query-tagged multipart upload returned %s: %s", multipartResp.Status, multipartBody)
+	}
+	var multipartResult InitiateMultipartUploadResponse
+	if err = xml.Unmarshal(multipartBody, &multipartResult); err != nil || multipartResult.UploadID == "" {
+		c.Fatalf("invalid query-tagged multipart response: uploadID=%q err=%v", multipartResult.UploadID, err)
+	}
+	if err = (minio.Core{Client: s.client}).AbortMultipartUpload(ctx, bucket, multipartObject, multipartResult.UploadID); err != nil {
+		c.Fatalf("unable to clean up query-tagged multipart upload: %v", err)
+	}
+
 	c.mustPutObjectWithTags(ctx, uClient, bucket, object)
 	c.mustGetObject(ctx, uClient, bucket, object)
+	objectInfo, err := s.client.StatObject(ctx, bucket, object, minio.StatObjectOptions{})
+	if err != nil {
+		c.Fatalf("unable to stat object for conditional GET: %v", err)
+	}
+	presignedGet, err := uClient.PresignedGetObject(ctx, bucket, object, time.Minute, nil)
+	if err != nil {
+		c.Fatalf("unable to presign conditional GET: %v", err)
+	}
+	getReq, err := http.NewRequestWithContext(ctx, http.MethodGet, presignedGet.String(), nil)
+	if err != nil {
+		c.Fatalf("unable to build conditional GET: %v", err)
+	}
+	getReq.Header.Set(xhttp.IfNoneMatch, `"`+objectInfo.ETag+`"`)
+	getResp := httptest.NewRecorder()
+	s.testServer.Server.Config.Handler.ServeHTTP(getResp, getReq)
+	if getResp.Code != http.StatusNotModified || getResp.Body.Len() != 0 {
+		c.Fatalf("conditional GET returned status %d with body %q", getResp.Code, getResp.Body.String())
+	}
+	replacementTags, err := tags.NewTags(map[string]string{"security": "public", "reviewed": "yes"}, true)
+	if err != nil {
+		c.Fatalf("unable to build replacement tags: %v", err)
+	}
+	if err = uClient.PutObjectTagging(ctx, bucket, object, replacementTags, minio.PutObjectTaggingOptions{}); err != nil {
+		c.Fatalf("user is unable to replace object tags: %v", err)
+	}
 
 	assumeRole := cr.STSAssumeRole{
 		Client:      s.TestSuiteCommon.client,
@@ -502,6 +616,9 @@ func (s *TestSuiteIAM) TestSTSWithTags(c *check) {
 	if err = minioClient.RemoveObject(ctx, bucket, object, minio.RemoveObjectOptions{}); err != nil {
 		c.Fatalf("user is unable to delete the object: %v", err)
 	}
+	if err = minioClient.RemoveObject(ctx, bucket, queryObject, minio.RemoveObjectOptions{}); err != nil {
+		c.Fatalf("user is unable to delete the query-tagged object: %v", err)
+	}
 }
 
 func (s *TestSuiteIAM) TestSTS(c *check) {
@@ -1948,9 +2065,7 @@ func TestSTSLDAPLoginRateLimiterCleanup(t *testing.T) {
 }
 
 func TestWriteSTSThrottledResponse(t *testing.T) {
-	req := httptest.NewRequest(http.MethodPost, "http://minio.test", strings.NewReader(""))
 	rr := httptest.NewRecorder()
-	req = req.WithContext(newContext(req, rr, "test-throttle"))
 
 	writeSTSThrottledResponse(rr)
 
diff --git a/internal/handlers/proxy.go b/internal/handlers/proxy.go
index f095b1fdb..886101a62 100644
--- a/internal/handlers/proxy.go
+++ b/internal/handlers/proxy.go
@@ -85,6 +85,17 @@ func GetSourceScheme(r *http.Request) string {
 	return scheme
 }
 
+// SECURITY NOTE: these headers are trusted from any peer. There is no
+// trusted-proxy boundary, X-Forwarded-For is honoured by default, and X-Real-IP
+// and Forwarded are not gated at all, so any client that can reach the server
+// directly can set the address the rest of the process believes it came from.
+// That includes aws:SourceIp, which means an IpAddress policy condition is not
+// enforceable on a directly reachable deployment - put MinIO behind a proxy
+// that overwrites these headers, or set _MINIO_API_XFF_HEADER=off and keep the
+// other two out at the edge. Adding a trusted-proxy allowlist here would change
+// what every deployment behind a load balancer resolves to, so it is recorded
+// rather than changed.
+//
 // GetSourceIPFromHeaders retrieves the IP from the X-Forwarded-For, X-Real-IP
 // and RFC7239 Forwarded headers (in that order)
 func GetSourceIPFromHeaders(r *http.Request) string {