GHSA-68j5-4m99-w9w9 File Browser has an Authorization Policy Bypass in Public Share Download Flow

• Go https://github.com/filebrowser/filebrowser: <= 2.61.0 (no fix yet)

Summary A permission enforcement flaw allows users without download privileges (`download=false`) to still expose and retrieve file content via public share links when they retain share privileges (`share=true`). This bypasses intended access control policy and enables unauthorized data exfiltration to unauthenticated users. Where download restrictions are used for data-loss prevention or role separation. Details The backend applies inconsistent authorization checks across download paths: • Direct raw download correctly enforces `Perm.Download`: • [raw.go](filebrowser/http/raw.go:82) • Share creation only enforces `Perm.Share`: • [share.go](filebrowser/http/share.go:21) • Public share/download handlers serve shared content without verifying owner `Perm.Download`: • public.go(filebrowser/http/public.go:18) • public.go(filebrowser/http/public.go:116) As a result, a user who is blocked from direct downloads can create a share and obtain the same file via `/api/public/dl/`. PoC 1. Create a non-admin user with: • `perm.share = true` • `perm.download = false` 2. Login as that user and upload a PDF file: • `POST /api/resources/nodl_secret_.pdf` with `Content-Type: application/pdf` 3. Verify direct raw download is denied: • `GET /api/raw/nodl_secret_.pdf` • Expected and observed: `202 Accepted` (blocked) 4. Create share for same file: • `POST /api/share/nodl_secret_.pdf` • Observed: `200`, response includes `hash` (example: `qxfK3JMG`) 5. Download publicly without authentication: • `GET /api/public/dl/` • Observed (vulnerable): `200`, `Content-Type: application/pdf`, and PDF bytes are returned Live evidence captured (March 1, 2026): • `create user`: `201` • `create file`: `200` • `direct /api/raw`: `202 Accepted` • `create share`: `200` • `public download /api/public/dl/mxK-ppZb`: `200` • `public download content-type`: `application/pdf` • `public download body length`: `327` bytes Impact This is an access control / authorization policy bypass vulnerability. • Who can exploit: Any authenticated user granted `share=true` but denied `download`. • Who is impacted: Operators and organizations relying on download restrictions to prevent data export. • What can happen: Restricted users can still distribute and retrieve files publicly, including unauthenticated access through share URLs.