diff --git a/cmd/auth-handler-unread-tags_test.go b/cmd/auth-handler-unread-tags_test.go
new file mode 100644
index 000000000..16a45dc66
--- /dev/null
+++ b/cmd/auth-handler-unread-tags_test.go
@@ -0,0 +1,246 @@
+// Copyright (c) 2026 Denis Babchuk
+//
+// 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"
+	"encoding/xml"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+
+	"github.com/minio/minio/internal/auth"
+	xhttp "github.com/minio/minio/internal/http"
+	"github.com/pgsty/silo-pkg/v3/policy"
+)
+
+// objectReadFault takes the first n drives of the set that holds object
+// offline for the metadata reads of that object only, so that IAM and bucket
+// metadata stay readable. It returns a function that restores the drives.
+func objectReadFault(z *erasureServerPools, bucket, object string, n int) func() {
+	pool := z.serverPools[0]
+	setIndex := pool.getHashedSetIndex(object)
+	pool.erasureDisksMu.Lock()
+	defer pool.erasureDisksMu.Unlock()
+	previous := pool.erasureDisks[setIndex]
+	disks := append([]StorageAPI(nil), previous...)
+	for i := range n {
+		disks[i] = consistencyReadFaultDisk{StorageAPI: disks[i], bucket: bucket, object: object}
+	}
+	pool.erasureDisks[setIndex] = disks
+	return func() {
+		pool.erasureDisksMu.Lock()
+		pool.erasureDisks[setIndex] = previous
+		pool.erasureDisksMu.Unlock()
+	}
+}
+
+// A caller allowed to read an object only through s3:ExistingObjectTag must
+// get the storage error, which clients retry, and not AccessDenied, when the
+// object's tags cannot be read because read quorum is lost. A caller that no
+// tags would let through must still get AccessDenied, and nothing changes
+// while the tags can be read.
+func TestExistingObjectTagAuthReadQuorumLost(t *testing.T) {
+	ctx, cancel := context.WithCancel(t.Context())
+	defer cancel()
+	obj, dirs, err := prepareErasure16(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	z := obj.(*erasureServerPools)
+	previous := newObjectLayerFn()
+	setObjectLayer(z)
+	defer func() {
+		z.Shutdown(context.Background())
+		removeRoots(dirs)
+		setObjectLayer(previous)
+	}()
+	bucket, router, err := initAPIHandlerTest(ctx, z, nil, MakeBucketOptions{})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	statement := func(effect, resource, conditions string) string {
+		st := fmt.Sprintf(`{"Effect": %q, "Action": ["s3:GetObject", "s3:PutObjectTagging"], "Resource": ["arn:aws:s3:::%s/%s"]`,
+			effect, bucket, resource)
+		if conditions != "" {
+			st += `, "Condition": ` + conditions
+		}
+		return st + "}"
+	}
+	tagStatement := func(effect, resource, value string) string {
+		return statement(effect, resource, fmt.Sprintf(`{"StringEquals": {"s3:ExistingObjectTag/k": %q}}`, value))
+	}
+	newUser := func(statements ...string) auth.Credentials {
+		return newDeleteAuthzPolicyUser(t, "", bucket, "["+strings.Join(statements, ",")+"]")
+	}
+	newServiceAccount := func(parent auth.Credentials, statements string) auth.Credentials {
+		sessionPolicy, err := policy.ParseConfig(strings.NewReader(`{"Version": "2012-10-17", "Statement": [` + statements + `]}`))
+		if err != nil {
+			t.Fatal(err)
+		}
+		cred, _, err := globalIAMSys.NewServiceAccount(ctx, parent.AccessKey, nil, newServiceAccountOpts{sessionPolicy: sessionPolicy})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return cred
+	}
+
+	type user struct {
+		name  string
+		creds auth.Credentials
+		// The status with the object's tags readable and with read quorum
+		// lost: 200 and 503 for a caller that some tags let through, 403
+		// and 403 for a caller that none do.
+		healthy, quorumLost int
+	}
+	allowedByTags := func(name string, creds auth.Credentials) user {
+		return user{name, creds, http.StatusOK, http.StatusServiceUnavailable}
+	}
+	deniedByAnyTags := func(name string, creds auth.Credentials) user {
+		return user{name, creds, http.StatusForbidden, http.StatusForbidden}
+	}
+	// Each case below that tests a tag key of its own uses a key no other
+	// policy asks for.
+	ownerCondition := `{"StringEquals": {"s3:ExistingObjectTag/owner": "${aws:username}"}}`
+	owner := newUser(statement("Allow", "*", ownerCondition))
+	users := []user{
+		// Allowed only while the object carries k=v.
+		allowedByTags("tagged", newUser(tagStatement("Allow", "*", "v"))),
+		// Allowed while the object carries a tag np, whatever its value.
+		allowedByTags("nullFalse", newUser(statement("Allow", "*", `{"Null": {"s3:ExistingObjectTag/np": "false"}}`))),
+		// Allowed while a tag ne is there and is not w.
+		allowedByTags("notEquals", newUser(statement("Allow", "*",
+			`{"Null": {"s3:ExistingObjectTag/ne": "false"}, "StringNotEquals": {"s3:ExistingObjectTag/ne": "w"}}`))),
+		// Allowed while every value of tag fa differs from w; that needs a tag fa.
+		allowedByTags("forAllNotEquals", newUser(statement("Allow", "*", `{"ForAllValues:StringNotEquals": {"s3:ExistingObjectTag/fa": "w"}}`))),
+		// Allowed while the object is tagged with the caller's name.
+		allowedByTags("owner", owner),
+		// Allowed, but denied unless the object carries du=1.
+		allowedByTags("denyUnlessTagged", newUser(statement("Allow", "*", ""),
+			statement("Deny", "*", `{"StringNotEquals": {"s3:ExistingObjectTag/du": "1"}}`))),
+		// A service account whose parent asks for k=v and whose own policy
+		// asks for j=w: only an object carrying both lets it through.
+		allowedByTags("serviceAccount", newServiceAccount(newUser(tagStatement("Allow", "*", "v")),
+			statement("Allow", "*", `{"StringEquals": {"s3:ExistingObjectTag/j": "w"}}`))),
+
+		// Allowed only for k=w: the decision still depends on the tags.
+		{"otherValue", newUser(tagStatement("Allow", "*", "w")), http.StatusForbidden, http.StatusServiceUnavailable},
+
+		// Allowed for k=v under another prefix only.
+		deniedByAnyTags("otherPrefix", newUser(tagStatement("Allow", "other/*", "v"))),
+		// Allowed and denied for k=v alike.
+		deniedByAnyTags("allowDeny", newUser(tagStatement("Allow", "*", "v"), tagStatement("Deny", "*", "v"))),
+		// Allowed only without a tag nc that is 1.
+		deniedByAnyTags("nullConflict", newUser(statement("Allow", "*",
+			`{"Null": {"s3:ExistingObjectTag/nc": "true"}, "StringEquals": {"s3:ExistingObjectTag/nc": "1"}}`))),
+		// Tagged with the caller's name, under another prefix only.
+		deniedByAnyTags("ownerPrefix", newUser(statement("Allow", "other/*", ownerCondition))),
+		// Denied unless the object carries db=1, and denied if it does.
+		deniedByAnyTags("denyBoth", newUser(statement("Allow", "*", ""),
+			statement("Deny", "*", `{"StringNotEquals": {"s3:ExistingObjectTag/db": "1"}}`),
+			statement("Deny", "*", `{"StringEquals": {"s3:ExistingObjectTag/db": "1"}}`))),
+		// The parent asks for k=v and the service account for k=x.
+		deniedByAnyTags("serviceAccountConflict", newServiceAccount(newUser(tagStatement("Allow", "*", "v")),
+			tagStatement("Allow", "*", "x"))),
+	}
+
+	const object, missing = "tagged", "missing"
+	if _, err := z.PutObject(ctx, bucket, object, mustGetPutObjReader(t, bytes.NewReader([]byte("data")), 4, "", ""),
+		ObjectOptions{UserDefined: map[string]string{xhttp.AmzObjectTagging: "k=v&j=w&np=1&ne=1&fa=1&du=1&owner=" + owner.AccessKey}}); err != nil {
+		t.Fatal(err)
+	}
+	// Anonymous reads are allowed by the bucket policy while the object carries k=v.
+	if _, err := globalBucketMetadataSys.Update(ctx, bucket, bucketPolicyConfig, []byte(`{"Version": "2012-10-17", "Statement": [
+  {"Effect": "Allow", "Principal": {"AWS": ["*"]}, "Action": ["s3:GetObject"], "Resource": ["arn:aws:s3:::`+bucket+`/*"],
+   "Condition": {"StringEquals": {"s3:ExistingObjectTag/k": "v"}}}]}`)); err != nil {
+		t.Fatal(err)
+	}
+
+	type request struct {
+		name           string
+		method, target string
+		header         map[string]string
+		body           []byte
+	}
+	objectURL := getGetObjectURL("", bucket, object)
+	get := request{"GET", http.MethodGet, objectURL, nil, nil}
+	head := request{"HEAD", http.MethodHead, objectURL, nil, nil}
+	taggingURL := makeTestTargetURL("", bucket, object, url.Values{"tagging": []string{""}})
+	taggingBody := []byte(`<Tagging><TagSet><Tag><Key>k</Key><Value>v</Value></Tag></TagSet></Tagging>`)
+	putTagging := request{"PutObjectTagging", http.MethodPut, taggingURL, nil, taggingBody}
+	check := func(stage string, creds auth.Credentials, name string, req request, want int) {
+		t.Helper()
+		var rec *httptest.ResponseRecorder
+		if creds.AccessKey == "" {
+			anonymous, err := newTestRequest(req.method, req.target, 0, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			rec = httptest.NewRecorder()
+			router.ServeHTTP(rec, anonymous)
+		} else {
+			var body io.ReadSeeker
+			if req.body != nil {
+				body = bytes.NewReader(req.body)
+			}
+			signed, err := newTestSignedRequestV4(req.method, req.target, int64(len(req.body)), body, creds.AccessKey, creds.SecretKey, req.header)
+			if err != nil {
+				t.Fatal(err)
+			}
+			rec = httptest.NewRecorder()
+			router.ServeHTTP(rec, signed)
+		}
+		if rec.Code != want {
+			var apiErr APIErrorResponse
+			_ = xml.Unmarshal(rec.Body.Bytes(), &apiErr)
+			t.Errorf("%s: %s by %s: status %d %s, want %d", stage, req.name, name, rec.Code, apiErr.Code, want)
+		}
+	}
+
+	var anonymous auth.Credentials
+	for _, u := range users {
+		check("healthy", u.creds, u.name, get, u.healthy)
+	}
+	check("healthy", anonymous, "anonymous", get, http.StatusOK)
+	// The tags were read and allow the request: the range error is the answer.
+	check("healthy", users[0].creds, users[0].name,
+		request{"GET bytes=100-200", http.MethodGet, objectURL, map[string]string{xhttp.Range: "bytes=100-200"}, nil},
+		http.StatusRequestedRangeNotSatisfiable)
+	// Without an object there are no tags: AccessDenied, as before.
+	missingURL := getGetObjectURL("", bucket, missing)
+	check("missing key", users[0].creds, users[0].name, request{"GET", http.MethodGet, missingURL, nil, nil}, http.StatusForbidden)
+	check("missing key", users[0].creds, users[0].name, request{"HEAD", http.MethodHead, missingURL, nil, nil}, http.StatusForbidden)
+
+	defer objectReadFault(z, bucket, object, 10)()
+	if _, err := z.GetObjectInfo(ctx, bucket, object, ObjectOptions{}); !isErrReadQuorum(err) {
+		t.Fatalf("GetObjectInfo with 10 of 16 drives failing: %v, want InsufficientReadQuorum", err)
+	}
+	for _, req := range []request{get, head, putTagging} {
+		for _, u := range users {
+			check("read quorum lost", u.creds, u.name, req, u.quorumLost)
+		}
+	}
+	check("read quorum lost", anonymous, "anonymous", get, http.StatusServiceUnavailable)
+	check("read quorum lost", anonymous, "anonymous", head, http.StatusServiceUnavailable)
+}