GHSA-mr74-928f-rw69 FileBrowser has Path Traversal in Public Share Links that Exposes Files Outside Shared Directory

• Go github.com/filebrowser/filebrowser/v2: < 2.61.0 → fixed in 2.61.0

Summary When a user creates a public share link for a directory, the `withHashFile` middleware in `http/public.go` (line 59) uses `filepath.Dir(link.Path)` to compute the `BasePathFs` root. This sets the filesystem root to the parent directory instead of the shared directory itself, allowing anyone with the share link to browse and download files from all sibling directories. Details In `http/public.go` lines 52-64, the `withHashFile` function handles public share link requests: ```go basePath := link.Path // e.g. "/documents/shared" filePath := "" if file.IsDir { basePath = filepath.Dir(basePath) // BUG: becomes "/documents" (parent!) filePath = ifPath } d.user.Fs = afero.NewBasePathFs(d.user.Fs, basePath) ``` When a directory at `/documents/shared` is shared, `filepath.Dir("/documents/shared")` evaluates to `"/documents"`. The `BasePathFs` is then rooted at the parent directory `/documents/`, giving the share link access to everything under `/documents/` - not just the intended `/documents/shared/`. This affects both `publicShareHandler` (directory listing via `/api/public/share/{hash}`) and `publicDlHandler` (file download via `/api/public/dl/{hash}/path`). PoC 1. Set up filebrowser with a user whose scope contains: 2. - `/documents/shared/public-file.txt` (intended to be shared) 3. - `/documents/secrets/passwords.txt` (NOT intended to be shared) 4. - `/documents/private/financial.csv` (NOT intended to be shared) 2. Create a public share link for the directory `/documents/shared` (via POST `/api/share/documents/shared`) 3. Access the share link: `GET /api/public/share/{hash}` 4. - Expected: Lists only contents of `/documents/shared/` 5. - Actual: Lists contents of `/documents/` (parent), revealing `secrets/`, `private/`, and `shared/` directories 4. Download sibling files: `GET /api/public/dl/{hash}/secrets/passwords.txt` 5. - Expected: 404 or 403 (file outside share scope) 6. - Actual: 200 with file contents (sibling file downloaded successfully) Standalone Go test reproducing the exact vulnerable code path with `afero.NewBasePathFs`: ```go func TestShareScopeEscape(t *testing.T) { baseFs := afero.NewMemMapFs() afero.WriteFile(baseFs, "/documents/shared/public.txt", []byte("public"), 0644) afero.WriteFile(baseFs, "/documents/secrets/passwords.txt", []byte("admin:hunter2"), 0644) linkPath := "/documents/shared" basePath := filepath.Dir(linkPath) // BUG: "/documents" scopedFs := afero.NewBasePathFs(baseFs, basePath) // Sibling file is accessible through the share: f, err := scopedFs.Open("/secrets/passwords.txt") // err is nil - file accessible! Content: "admin:hunter2" } ``` This test passes, confirming the vulnerability. Impact Unauthenticated information disclosure (CWE-200, CWE-706). Anyone with a public share link for a directory can: • Browse all sibling directories and files of the shared directory • - Download any file within the parent directory scope • - This works without authentication (public shares) or after providing the share password (password-protected shares) All filebrowser v2.x installations that use directory sharing are affected. Recommended Fix Remove the `filepath.Dir()` call and use `link.Path` directly as the `BasePathFs` root: ```go if file.IsDir { // Don't change basePath - keep it as link.Path filePath = ifPath } d.user.Fs = afero.NewBasePathFs(d.user.Fs, basePath) ``` Affected commit: e3d00d591b567a8bfe3b02e42ba586859002c77d (latest) File: `http/public.go`, line 59