diff --git a/server/db/mysql/adapter.go b/server/db/mysql/adapter.go
index 89e049c..9de4963 100644
--- a/server/db/mysql/adapter.go
+++ b/server/db/mysql/adapter.go
@@ -72,6 +72,27 @@ func quoteIdent(name string) string {
 	return "`" + strings.ReplaceAll(name, "`", "``") + "`"
 }
 
+func parseFileUID(fid string) t.Uid {
+	name := strings.TrimSpace(fid)
+	id := t.ParseUid(name)
+	if !id.IsZero() {
+		return id
+	}
+	if dot := strings.LastIndexByte(name, '.'); dot > 0 {
+		ext := name[dot+1:]
+		if len(ext) == 0 || len(ext) > 16 {
+			return t.ZeroUid
+		}
+		for _, r := range ext {
+			if (r < 'A' || r > 'Z') && (r < 'a' || r > 'z') && (r < '0' || r > '9') {
+				return t.ZeroUid
+			}
+		}
+		return t.ParseUid(name[:dot])
+	}
+	return t.ZeroUid
+}
+
 type configType struct {
 	// DB connection settings.
 	// See https://pkg.go.dev/github.com/go-sql-driver/mysql#Config
@@ -4994,7 +5015,7 @@ func (a *adapter) FileFinishUpload(fd *t.FileDef, success bool, size int64) (*t.
 
 // FileGet fetches a record of a specific file
 func (a *adapter) FileGet(fid string) (*t.FileDef, error) {
-	id := t.ParseUid(fid)
+	id := parseFileUID(fid)
 	if id.IsZero() {
 		return nil, t.ErrMalformed
 	}
@@ -5188,7 +5209,7 @@ func (a *adapter) FileUserHasAccess(fid string, uid t.Uid) (bool, error) {
 	if uid.IsZero() {
 		return false, t.ErrMalformed
 	}
-	fileID := t.ParseUid(fid)
+	fileID := parseFileUID(fid)
 	if fileID.IsZero() {
 		return false, t.ErrMalformed
 	}
diff --git a/server/db/mysql/adapter_fileid_test.go b/server/db/mysql/adapter_fileid_test.go
new file mode 100644
index 0000000..5834821
--- /dev/null
+++ b/server/db/mysql/adapter_fileid_test.go
@@ -0,0 +1,26 @@
+//go:build mysql
+// +build mysql
+
+package mysql
+
+import (
+	"testing"
+
+	"github.com/tinode/chat/server/store/types"
+)
+
+func TestParseFileUIDStripsPublicExtension(t *testing.T) {
+	uid := types.ParseUid("scH0N8guCHk")
+	if uid.IsZero() {
+		t.Fatal("test UID failed to parse")
+	}
+	if got := parseFileUID("scH0N8guCHk.bin"); got != uid {
+		t.Fatalf("parseFileUID()=%q, want %q", got.String(), uid.String())
+	}
+	if got := parseFileUID("scH0N8guCHk.jpg"); got != uid {
+		t.Fatalf("parseFileUID()=%q, want %q", got.String(), uid.String())
+	}
+	if got := parseFileUID("scH0N8guCHk"); got != uid {
+		t.Fatalf("parseFileUID()=%q, want %q", got.String(), uid.String())
+	}
+}
diff --git a/server/db/mysql/tenant_adapter.go b/server/db/mysql/tenant_adapter.go
index df8a3ae..b82a5fb 100644
--- a/server/db/mysql/tenant_adapter.go
+++ b/server/db/mysql/tenant_adapter.go
@@ -7678,7 +7678,7 @@ func (a *adapter) TenantFileGet(id t.TenantID, fid string) (*t.FileDef, error) {
 		file, err := a.FileGet(fid)
 		return stampTenantFile(id, file), err
 	}
-	fileID := t.ParseUid(fid)
+	fileID := parseFileUID(fid)
 	if fileID.IsZero() {
 		return nil, t.ErrMalformed
 	}
@@ -7859,7 +7859,7 @@ func (a *adapter) TenantFileUserHasAccess(id t.TenantID, fid string, uid t.Uid)
 	if a.tenantScopedDB {
 		return a.FileUserHasAccess(fid, uid)
 	}
-	fileID := t.ParseUid(fid)
+	fileID := parseFileUID(fid)
 	if fileID.IsZero() {
 		return false, t.ErrMalformed
 	}
diff --git a/server/hdl_files.go b/server/hdl_files.go
index b38b3c2..a06d2e3 100644
--- a/server/hdl_files.go
+++ b/server/hdl_files.go
@@ -113,6 +113,11 @@ func largeFileServeHTTP(wrt http.ResponseWriter, req *http.Request) {
 		return
 	}
 
+	if err = authorizeLargeFileRequestURL(principal.TenantID, principal.UID, req.URL.String()); err != nil {
+		writeHttpResponse(decodeStoreError(err, "", now, nil), err)
+		return
+	}
+
 	// Check if media handler redirects or adds headers.
 	headers, statusCode, err := mh.Headers(principal.TenantID, req.Method, req.URL, req.Header, true)
 	if err != nil {
@@ -517,6 +522,21 @@ func (*grpcNodeServer) LargeFileServe(req *pbx.FileDownReq, stream pbx.Node_Larg
 	return err
 }
 
+func authorizeLargeFileRequestURL(tenantID types.TenantID, uid types.Uid, rawURL string) error {
+	if store.Store == nil {
+		return types.ErrUnsupported
+	}
+	fid := store.Store.GetMediaHandler().GetIdFromUrl(rawURL)
+	if fid.IsZero() {
+		return types.ErrNotFound
+	}
+	fd, err := store.Files.Get(tenantID, fid.String())
+	if err != nil {
+		return err
+	}
+	return authorizeLargeFileDownload(tenantID, uid, rawURL, fd)
+}
+
 func authorizeLargeFileDownload(tenantID types.TenantID, uid types.Uid, rawURL string, fd *types.FileDef) error {
 	if fd == nil {
 		return types.ErrNotFound
diff --git a/server/hdl_files_test.go b/server/hdl_files_test.go
index a2abea1..8621038 100644
--- a/server/hdl_files_test.go
+++ b/server/hdl_files_test.go
@@ -22,12 +22,15 @@ import (
 )
 
 type testLargeFileMediaHandler struct {
-	def  *types.FileDef
-	data string
+	def           *types.FileDef
+	data          string
+	fid           types.Uid
+	headersCalled bool
 }
 
 func (h *testLargeFileMediaHandler) Init(string) error { return nil }
 func (h *testLargeFileMediaHandler) Headers(types.TenantID, string, *url.URL, http.Header, bool) (http.Header, int, error) {
+	h.headersCalled = true
 	return nil, 0, nil
 }
 func (h *testLargeFileMediaHandler) Upload(def *types.FileDef, file io.Reader) (string, int64, error) {
@@ -43,7 +46,7 @@ func (h *testLargeFileMediaHandler) Download(types.TenantID, string) (*types.Fil
 }
 func (h *testLargeFileMediaHandler) Delete([]string) error { return nil }
 func (h *testLargeFileMediaHandler) GetIdFromUrl(string) types.Uid {
-	return types.ZeroUid
+	return h.fid
 }
 
 func TestAuthFileRequestFromSessionRequiresTenant(t *testing.T) {
@@ -144,6 +147,43 @@ func TestAuthorizeLargeFileDownloadRejectsCrossTenant(t *testing.T) {
 	}
 }
 
+func TestAuthorizeLargeFileRequestURLRequiresAccessBeforeRedirect(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+
+	oldStore := store.Store
+	oldFiles := store.Files
+	defer func() {
+		store.Store = oldStore
+		store.Files = oldFiles
+	}()
+
+	fid := types.Uid(100)
+	handler := &testLargeFileMediaHandler{fid: fid}
+	mockStore := mock_store.NewMockPersistentStorageInterface(ctrl)
+	files := mock_store.NewMockFilePersistenceInterface(ctrl)
+	store.Store = mockStore
+	store.Files = files
+
+	fd := &types.FileDef{
+		ObjHeader: types.ObjHeader{Id: fid.String(), UpdatedAt: time.Date(2026, 8, 13, 9, 0, 0, 0, time.UTC)},
+		TenantID:  7,
+		Status:    types.UploadCompleted,
+		MimeType:  "image/jpeg",
+		Location:  "image.jpeg",
+	}
+	mockStore.EXPECT().GetMediaHandler().Return(handler)
+	files.EXPECT().Get(types.TenantID(7), fid.String()).Return(fd, nil)
+	files.EXPECT().UserHasAccess(types.TenantID(7), fid.String(), types.Uid(42)).Return(false, nil)
+
+	if err := authorizeLargeFileRequestURL(7, 42, "/v0/file/s/file.jpeg"); err != types.ErrPermissionDenied {
+		t.Fatalf("expected permission denied, got %v", err)
+	}
+	if handler.headersCalled {
+		t.Fatal("media headers should not be called by authorization helper")
+	}
+}
+
 func TestContentDispositionAttachmentSanitizesName(t *testing.T) {
 	fd := &types.FileDef{
 		ObjHeader: types.ObjHeader{Id: types.Uid(100).String()},
diff --git a/server/media/oss/oss.go b/server/media/oss/oss.go
index 4e75174..8ee3fa0 100644
--- a/server/media/oss/oss.go
+++ b/server/media/oss/oss.go
@@ -258,7 +258,7 @@ func (oh *ossHandler) Headers(tenantID types.TenantID, method string, url *url.U
 			"ETag":          {`"` + fdef.ETag + `"`},
 			"Content-Type":  {"application/json; charset=utf-8"},
 			"Cache-Control": {oh.conf.CacheControl},
-		}, http.StatusPermanentRedirect, nil
+		}, http.StatusFound, nil
 	}
 	return nil, 0, nil
 }
diff --git a/server/media/s3/s3.go b/server/media/s3/s3.go
index 41e7539..bf65d37 100644
--- a/server/media/s3/s3.go
+++ b/server/media/s3/s3.go
@@ -248,16 +248,14 @@ func (ah *awshandler) Headers(tenantID types.TenantID, method string, url *url.U
 	}
 
 	if redirURL != "" {
-		// Return presigned URL with 308 Permanent redirect. Let the client cache the response.
-		// The original URL will stop working after a short period of time to prevent use of Tinode
-		// as a free file server.
+		// Return a temporary redirect to a short-lived presigned URL.
 		return http.Header{
 				"Location":      {redirURL},
 				"ETag":          {`"` + fdef.ETag + `"`},
 				"Content-Type":  {"application/json; charset=utf-8"},
 				"Cache-Control": {ah.conf.CacheControl},
 			},
-			http.StatusPermanentRedirect, nil
+			http.StatusFound, nil
 	}
 	return nil, 0, nil
 }