diff --git a/weed/s3api/s3api_object_handlers.go b/weed/s3api/s3api_object_handlers.go
index ab01cfda36..4c16300cd5 100644
--- a/weed/s3api/s3api_object_handlers.go
+++ b/weed/s3api/s3api_object_handlers.go
@@ -2401,23 +2401,29 @@ func (s3a *S3ApiServer) setResponseHeaders(w http.ResponseWriter, r *http.Reques
 	// Set custom headers from entry.Extended (user metadata)
 	// Use direct map assignment to preserve original header casing (matches proxy behavior)
 	if entry.Extended != nil {
+		extAmzPrefixLower := strings.ToLower(s3_constants.ExtAmzPrefix)
+		taggingPrefixLower := strings.ToLower(s3_constants.AmzObjectTaggingPrefix)
 		for k, v := range entry.Extended {
-			// Skip internal SeaweedFS headers
-			if !strings.HasPrefix(k, "xattr-") && !s3_constants.IsSeaweedFSInternalHeader(k) {
-				// Support backward compatibility: migrate old non-canonical format to canonical format
-				// OLD: "x-amz-meta-foo" → NEW: "X-Amz-Meta-foo" (preserving suffix case)
-				headerKey := k
-				if len(k) >= 11 && strings.EqualFold(k[:11], "x-amz-meta-") {
-					// Normalize to AWS S3 format: "X-Amz-Meta-" prefix with lowercase suffix
-					// AWS S3 returns user metadata with the suffix in lowercase
-					suffix := k[len("x-amz-meta-"):]
-					headerKey = s3_constants.AmzUserMetaPrefix + strings.ToLower(suffix)
-					if glog.V(4) && k != headerKey {
-						glog.Infof("Normalizing user metadata header %q to %q in response", k, headerKey)
-					}
-				}
-				w.Header()[headerKey] = []string{string(v)}
+			// Skip internal SeaweedFS headers, and the stored tag/ACL/lock
+			// metadata that belongs behind its own API (GetObjectTagging,
+			// GetObjectAcl, GetObjectRetention) instead of every reader.
+			lowerKey := strings.ToLower(k)
+			if strings.HasPrefix(lowerKey, "xattr-") || strings.HasPrefix(lowerKey, extAmzPrefixLower) || strings.HasPrefix(lowerKey, taggingPrefixLower) || s3_constants.IsSeaweedFSInternalHeader(lowerKey) {
+				continue
 			}
+			// Support backward compatibility: migrate old non-canonical format to canonical format
+			// OLD: "x-amz-meta-foo" → NEW: "X-Amz-Meta-foo" (preserving suffix case)
+			headerKey := k
+			if len(k) >= 11 && strings.EqualFold(k[:11], "x-amz-meta-") {
+				// Normalize to AWS S3 format: "X-Amz-Meta-" prefix with lowercase suffix
+				// AWS S3 returns user metadata with the suffix in lowercase
+				suffix := k[len("x-amz-meta-"):]
+				headerKey = s3_constants.AmzUserMetaPrefix + strings.ToLower(suffix)
+				if glog.V(4) && k != headerKey {
+					glog.Infof("Normalizing user metadata header %q to %q in response", k, headerKey)
+				}
+			}
+			w.Header()[headerKey] = []string{string(v)}
 		}
 	}
 
diff --git a/weed/s3api/s3api_object_handlers_response_headers_test.go b/weed/s3api/s3api_object_handlers_response_headers_test.go
new file mode 100644
index 0000000000..d2d010c5c2
--- /dev/null
+++ b/weed/s3api/s3api_object_handlers_response_headers_test.go
@@ -0,0 +1,66 @@
+package s3api
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
+	"github.com/seaweedfs/seaweedfs/weed/s3api/s3_constants"
+)
+
+// GetObject/HeadObject must expose only response headers AWS defines: user
+// metadata, standard entity headers and x-amz-tagging-count. Tag values live
+// behind GetObjectTagging and ACL/owner/lock state behind its own APIs; the
+// generic Extended echo must not hand them to any caller that can read the
+// object.
+func TestSetResponseHeadersFiltersInternalExtendedKeys(t *testing.T) {
+	s3a := &S3ApiServer{}
+	entry := &filer_pb.Entry{
+		Name:       "object",
+		Attributes: &filer_pb.FuseAttributes{Mtime: 100},
+		Extended: map[string][]byte{
+			s3_constants.AmzObjectTaggingPrefix + "project": []byte("alpha"),
+			s3_constants.AmzObjectTaggingPrefix + "owner":   []byte("y"),
+			"x-amz-tagging-sneaky":                        []byte("z"),
+			"seaweed-x-amz-acl":                           []byte("z"),
+			s3_constants.ExtAmzAclKey:                       []byte(`[{"Permission":"FULL_CONTROL"}]`),
+			s3_constants.ExtAmzOwnerKey:                     []byte("admin"),
+			s3_constants.ExtVersionIdKey:                    []byte("version-1"),
+			s3_constants.ExtObjectLockModeKey:               []byte("COMPLIANCE"),
+			s3_constants.ExtETagKey:                         []byte("d41d8cd98f00b204e9800998ecf8427e"),
+			s3_constants.SeaweedFSWriteId:                   []byte("write-id"),
+			"X-Amz-Meta-Foo":                               []byte("bar"),
+			"Cache-Control":                                []byte("no-cache"),
+			"xattr-user.note":                              []byte("n"),
+		},
+	}
+
+	for _, method := range []string{http.MethodGet, http.MethodHead} {
+		w := httptest.NewRecorder()
+		s3a.setResponseHeaders(w, httptest.NewRequest(method, "/bucket/object", nil), entry, 8)
+
+		for key := range w.Header() {
+			lowerKey := strings.ToLower(key)
+			if lowerKey == s3_constants.AmzTagCount {
+				continue
+			}
+			if strings.HasPrefix(lowerKey, strings.ToLower(s3_constants.ExtAmzPrefix)) {
+				t.Errorf("%s: internal header %q leaked into response", method, key)
+			}
+			if strings.HasPrefix(lowerKey, strings.ToLower(s3_constants.AmzObjectTaggingPrefix)) {
+				t.Errorf("%s: object tag value %q leaked into response", method, key)
+			}
+		}
+		if got := w.Header().Get(s3_constants.AmzTagCount); got != "2" {
+			t.Errorf("%s: tag count = %q, want 2", method, got)
+		}
+		if got := w.Header()["X-Amz-Meta-foo"]; len(got) != 1 || got[0] != "bar" {
+			t.Errorf("%s: user metadata dropped, X-Amz-Meta-foo = %v", method, got)
+		}
+		if got := w.Header().Get("Cache-Control"); got != "no-cache" {
+			t.Errorf("%s: Cache-Control = %q", method, got)
+		}
+	}
+}