diff --git a/chfs-ng/internal/api/server.go b/chfs-ng/internal/api/server.go
index 639e630..a6d5440 100644
--- a/chfs-ng/internal/api/server.go
+++ b/chfs-ng/internal/api/server.go
@@ -124,6 +124,13 @@ func writeJSONError(w http.ResponseWriter, status int, message string) {
 	_ = json.NewEncoder(w).Encode(map[string]string{"error": message})
 }
 func unsafePath(p string) bool {
+	// Reject traversal and NUL before any permission/storage resolution.
+	// URL.Query/FormValue has already performed the single HTTP decode, so
+	// double-encoded traversal remains a literal filename rather than being
+	// decoded again by this layer.
+	if strings.IndexByte(p, 0) >= 0 {
+		return true
+	}
 	p = strings.ReplaceAll(p, "\\", "/")
 	for _, part := range strings.Split(p, "/") {
 		if part == ".." {
@@ -258,8 +265,13 @@ func (s *Server) newdir(w http.ResponseWriter, r *http.Request) {
 }
 func (s *Server) rename(w http.ResponseWriter, r *http.Request) {
 	a := account(r, s)
-	old := strings.Trim(r.FormValue("old"), "/")
-	neu := strings.Trim(r.FormValue("new"), "/")
+	rawOld, rawNew := r.FormValue("old"), r.FormValue("new")
+	if unsafePath(rawOld) || unsafePath(rawNew) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
+	old := strings.Trim(rawOld, "/")
+	neu := strings.Trim(rawNew, "/")
 	if old == "" || neu == "" || !a.MaskFor(old).HasWrite() || !a.MaskFor(path.Dir(neu)).HasWrite() {
 		writeJSONError(w, http.StatusForbidden, "has no privilege")
 		return
@@ -280,6 +292,10 @@ func (s *Server) remove(w http.ResponseWriter, r *http.Request) {
 		items = r.Form["path"]
 	}
 	for _, raw := range items {
+		if unsafePath(raw) {
+			writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+			return
+		}
 		p := strings.Trim(strings.ReplaceAll(raw, "\\", "/"), "/")
 		if p == "" || !a.MaskFor(p).HasDelete() {
 			writeJSONError(w, http.StatusForbidden, "has no privilege")
@@ -319,7 +335,12 @@ func (s *Server) removePath(p string) error {
 }
 
 func (s *Server) exist(w http.ResponseWriter, r *http.Request) {
-	p := strings.Trim(strings.ReplaceAll(r.URL.Query().Get("file"), "\\", "/"), "/")
+	raw := r.URL.Query().Get("file")
+	if unsafePath(raw) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
+	p := strings.Trim(strings.ReplaceAll(raw, "\\", "/"), "/")
 	_, e := s.Store.Stat(p)
 	if e != nil {
 		w.WriteHeader(http.StatusNotFound)
@@ -372,8 +393,13 @@ func (s *Server) session(w http.ResponseWriter, r *http.Request) {
 
 func (s *Server) newtext(w http.ResponseWriter, r *http.Request) {
 	a := account(r, s)
-	dir := strings.Trim(strings.ReplaceAll(r.FormValue("filepath"), "\\", "/"), "/")
-	filename := strings.Trim(r.FormValue("title"), "/")
+	rawDir, rawTitle, rawFilename := r.FormValue("filepath"), r.FormValue("title"), r.FormValue("filename")
+	if unsafePath(rawDir) || unsafePath(rawTitle) || unsafePath(rawFilename) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
+	dir := strings.Trim(strings.ReplaceAll(rawDir, "\\", "/"), "/")
+	filename := strings.Trim(rawTitle, "/")
 	if filename == "" {
 		filename = strings.Trim(r.FormValue("filename"), "/")
 	}
@@ -398,8 +424,13 @@ func (s *Server) newtext(w http.ResponseWriter, r *http.Request) {
 }
 func (s *Server) updatetext(w http.ResponseWriter, r *http.Request) {
 	a := account(r, s)
-	dir := strings.Trim(r.FormValue("filepath"), "/")
-	name := strings.Trim(r.FormValue("filename"), "/")
+	rawDir, rawName := r.FormValue("filepath"), r.FormValue("filename")
+	if unsafePath(rawDir) || unsafePath(rawName) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
+	dir := strings.Trim(strings.ReplaceAll(rawDir, "\\", "/"), "/")
+	name := strings.Trim(strings.ReplaceAll(rawName, "\\", "/"), "/")
 	p := path.Join(dir, name)
 	if name == "" || !a.MaskFor(p).HasWrite() {
 		writeJSONError(w, http.StatusForbidden, "has no privilege")
@@ -424,7 +455,12 @@ func (s *Server) upload(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	a := account(r, s)
-	dir := strings.Trim(r.FormValue("folder"), "/")
+	rawDir := r.FormValue("folder")
+	if unsafePath(rawDir) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
+	dir := strings.Trim(strings.ReplaceAll(rawDir, "\\", "/"), "/")
 	if !a.MaskFor(dir).HasWrite() {
 		writeJSONError(w, http.StatusForbidden, "has no privilege")
 		return
@@ -433,7 +469,7 @@ func (s *Server) upload(w http.ResponseWriter, r *http.Request) {
 	for _, hs := range r.MultipartForm.File {
 		for _, h := range hs {
 			name := filepath.ToSlash(h.Filename)
-			if name == "" || strings.HasPrefix(name, "/") || strings.Contains(name, "../") || name == ".." {
+			if name == "" || strings.HasPrefix(name, "/") || unsafePath(name) {
 				http.Error(w, "invalid filename", 400)
 				return
 			}
@@ -466,7 +502,12 @@ func savePart(st storage.Storage, target string, h *multipart.FileHeader) error
 
 func (s *Server) upload2(w http.ResponseWriter, r *http.Request) {
 	a := account(r, s)
-	dir := strings.Trim(r.URL.Query().Get("folder"), "/")
+	rawDir := r.URL.Query().Get("folder")
+	if unsafePath(rawDir) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
+	dir := strings.Trim(strings.ReplaceAll(rawDir, "\\", "/"), "/")
 	if !a.MaskFor(dir).HasWrite() {
 		writeJSONError(w, http.StatusForbidden, "has no privilege")
 		return
@@ -480,7 +521,7 @@ func (s *Server) upload2(w http.ResponseWriter, r *http.Request) {
 		for _, h := range hs {
 			name := filepath.ToSlash(h.Filename)
 			name = strings.TrimPrefix(name, "/")
-			if name == "" || strings.Contains(name, "../") || name == ".." {
+			if name == "" || unsafePath(name) {
 				http.Error(w, "invalid filename", 400)
 				return
 			}
@@ -603,7 +644,12 @@ func (s *Server) shared(w http.ResponseWriter, r *http.Request) {
 }
 
 func (s *Server) preview(w http.ResponseWriter, r *http.Request) {
-	file := strings.Trim(strings.ReplaceAll(r.URL.Query().Get("file"), "\\", "/"), "/")
+	rawFile := r.URL.Query().Get("file")
+	if unsafePath(rawFile) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
+	file := strings.Trim(strings.ReplaceAll(rawFile, "\\", "/"), "/")
 	if file == "" {
 		http.Error(w, "file required", 400)
 		return
@@ -673,8 +719,12 @@ func (s *Server) serveFile(w http.ResponseWriter, r *http.Request, p string, att
 
 func (s *Server) downloadDir(w http.ResponseWriter, r *http.Request) {
 	a := account(r, s)
-	p := strings.TrimPrefix(r.URL.Path, "/chfs/downloaddir/")
-	p = strings.Trim(p, "/")
+	rawPath := strings.TrimPrefix(r.URL.Path, "/chfs/downloaddir/")
+	if unsafePath(rawPath) {
+		writeJSONError(w, http.StatusBadRequest, "invalid parameter")
+		return
+	}
+	p := strings.Trim(rawPath, "/")
 	if !a.MaskFor(p).HasRead() {
 		writeJSONError(w, http.StatusForbidden, "has no privilege")
 		return
@@ -765,8 +815,19 @@ func davStoragePath(name string) string {
 	return strings.Trim(p, "/")
 }
 
-func (f *webdavStorageFS) info(name string) (*webdav.FileInfo, error) {
+func davSafePath(name string) (string, error) {
 	p := davStoragePath(name)
+	if unsafePath(p) {
+		return "", webdav.NewHTTPError(http.StatusBadRequest, fmt.Errorf("invalid parameter"))
+	}
+	return p, nil
+}
+
+func (f *webdavStorageFS) info(name string) (*webdav.FileInfo, error) {
+	p, err := davSafePath(name)
+	if err != nil {
+		return nil, err
+	}
 	fi, err := f.store.Stat(p)
 	if err != nil {
 		return nil, err
@@ -775,7 +836,10 @@ func (f *webdavStorageFS) info(name string) (*webdav.FileInfo, error) {
 }
 
 func (f *webdavStorageFS) Open(ctx context.Context, name string) (io.ReadCloser, error) {
-	p := davStoragePath(name)
+	p, err := davSafePath(name)
+	if err != nil {
+		return nil, err
+	}
 	fi, err := f.store.Stat(p)
 	if err != nil {
 		return nil, err
@@ -791,7 +855,10 @@ func (f *webdavStorageFS) Stat(ctx context.Context, name string) (*webdav.FileIn
 }
 
 func (f *webdavStorageFS) ReadDir(ctx context.Context, name string, recursive bool) ([]webdav.FileInfo, error) {
-	root := davStoragePath(name)
+	root, err := davSafePath(name)
+	if err != nil {
+		return nil, err
+	}
 	var out []webdav.FileInfo
 	var walk func(string) error
 	walk = func(dir string) error {
@@ -817,7 +884,10 @@ func (f *webdavStorageFS) ReadDir(ctx context.Context, name string, recursive bo
 }
 
 func (f *webdavStorageFS) Create(ctx context.Context, name string, body io.ReadCloser, opts *webdav.CreateOptions) (*webdav.FileInfo, bool, error) {
-	p := davStoragePath(name)
+	p, err := davSafePath(name)
+	if err != nil {
+		return nil, false, err
+	}
 	_, statErr := f.store.Stat(p)
 	if statErr != nil && !os.IsNotExist(statErr) {
 		return nil, false, statErr
@@ -840,7 +910,10 @@ func (f *webdavStorageFS) Create(ctx context.Context, name string, body io.ReadC
 }
 
 func (f *webdavStorageFS) RemoveAll(ctx context.Context, name string, opts *webdav.RemoveAllOptions) error {
-	p := davStoragePath(name)
+	p, err := davSafePath(name)
+	if err != nil {
+		return err
+	}
 	if p == "" {
 		return fmt.Errorf("cannot remove storage root")
 	}
@@ -868,7 +941,10 @@ func (f *webdavStorageFS) RemoveAll(ctx context.Context, name string, opts *webd
 }
 
 func (f *webdavStorageFS) Mkdir(ctx context.Context, name string) error {
-	p := davStoragePath(name)
+	p, err := davSafePath(name)
+	if err != nil {
+		return err
+	}
 	if p == "" {
 		return fmt.Errorf("cannot create storage root")
 	}
@@ -881,8 +957,14 @@ func (f *webdavStorageFS) Mkdir(ctx context.Context, name string) error {
 }
 
 func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *webdav.CopyOptions) (bool, error) {
-	src := davStoragePath(name)
-	dst := davStoragePath(dest)
+	src, err := davSafePath(name)
+	if err != nil {
+		return false, err
+	}
+	dst, err := davSafePath(dest)
+	if err != nil {
+		return false, err
+	}
 	if opts != nil && opts.NoOverwrite {
 		if _, err := f.store.Stat(dst); err == nil {
 			return false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))
@@ -940,8 +1022,14 @@ func (f *webdavStorageFS) Copy(ctx context.Context, name, dest string, opts *web
 }
 
 func (f *webdavStorageFS) Move(ctx context.Context, name, dest string, opts *webdav.MoveOptions) (bool, error) {
-	src := davStoragePath(name)
-	dst := davStoragePath(dest)
+	src, err := davSafePath(name)
+	if err != nil {
+		return false, err
+	}
+	dst, err := davSafePath(dest)
+	if err != nil {
+		return false, err
+	}
 	if opts == nil || opts.NoOverwrite {
 		if _, err := f.store.Stat(dst); err == nil {
 			return false, webdav.NewHTTPError(http.StatusPreconditionFailed, fmt.Errorf("destination exists"))