GHSA-rh79-75qm-gwjr Gitea LFS Deploy-Key Privilege Escalation
Vulnerability Header| Field               | Value                                                       |
| ------------------- | ----------------------------------------------------------- |
| Vulnerability Title | Gitea LFS Deploy-Key Privilege Escalation                   |
| Severity Rating     | High                                                        |
| Bug Category        | Insufficient Authorization                                  |
| Location            | `services/lfs/server.go:268`, `routers/private/serv.go:275` |
| Affected Versions   | 1.25.5                                                      |Executive SummaryGitea's LFS server (`services/lfs/server.go:268`) uses the `UserID` embedded in an LFS JWT to make cross-repository authorization decisions via `LFSObjectAccessible()`. This would be safe if the JWT `UserID` always matched the actual requesting principal — but for deploy keys, `routers/private/serv.go:275` sets `UserID = repo.OwnerID` instead of any identity representing the deploy key itself. As a result, an attacker who holds a write deploy key for any single repo owned by a victim can obtain a legitimate JWT (via the standard SSH `git-lfs-authenticate` flow) that Gitea will honor as if the victim themselves were making the request. The attacker can then exfiltrate LFS objects from any private repo the victim owns — no admin credentials, no server secrets, no brute force required. If the victim is a site administrator, every LFS object on the entire Gitea instance is reachable. Deploy keys exist precisely to grant narrow, single-repo access to CI/CD systems; this vulnerability defeats that isolation entirely for LFS data.Root Cause AnalysisTechnical DescriptionThe vulnerability is a **trust-boundary confusion** across two independent subsystems. When a deploy key authenticates over SSH, `serv.go` sets `UserID = repo.OwnerID` because the code has no better representation for a deploy key identity (a `FIXME` comment acknowledges this). That `UserID` is baked verbatim into the LFS JWT by `cmd/serv.go`. The JWT is then consumed by `server.go`, which treats `claims.UserID` as the authenticated principal and loads that user object as `ctx.Doer`. When the batch upload handler encounters an object that exists on disk but isn't yet linked to the target repo, it calls `LFSObjectAccessible(ctx, ctx.Doer, oid)` — a global query across all repos the claimed user can see — to decide whether to silently create the cross-repo link. The JWT's `RepoID` claim is verified (so the request is correctly scoped to one repo at the HTTP level), but the `UserID` driving the cross-repo access decision is the repo *owner*, not the deploy key. The attacker ends up holding a valid, server-signed token that impersonates the victim for any LFS authorization check.First Faulty ConditionThe primary bug — where the JWT `UserID` is set incorrectly — is in `serv.go`:| File      | `routers/private/serv.go`                                                                         |
| --------- | ------------------------------------------------------------------------------------------------- |
| Line      | 275                                                                                               |
| Condition | Deploy key branch sets `results.UserID = repo.OwnerID`; the owner's UID is embedded in the JWT and later used as the authenticated principal for cross-repo privilege decisions in `server.go:268` |The secondary bug — where the tainted `UserID` is actually misused — is in `server.go`:| File      | `services/lfs/server.go`                                                                                                                                         |
| --------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Line      | 268                                                                                                                                                              |
| Condition | `LFSObjectAccessible(ctx, ctx.Doer, oid)` makes a cross-repo decision using the JWT `UserID`, which for deploy keys is the repo owner, not the deploy key holder |**Admin amplification:** if `victim.IsAdmin`, `models/git/lfs.go:226` short-circuits with a bare `COUNT(*)` over the entire `lfs_meta_object` table — no repo filter. A deploy key on any admin-owned repo reaches every LFS object on the instance.Exploitability AssessmentAttack Vector & Reachability| Attack vector               | Network                                                                                            |
| --------------------------- | -------------------------------------------------------------------------------------------------- |
| Authentication required     | Low: attacker must hold a write deploy key's private key material for any of victim's repositories |
| User interaction required   | None                                                                                               |
| Reachable in default config | No. Requires `LFS_START_SERVER = true`                                                             |
| Entry point(s)              | SSH `git-lfs-authenticate` command + HTTP LFS batch API                                            |The practical exploitability of this vulnerability is constrained by a second prerequisite that is independent of the authorization bypass itself: the attacker must know the SHA-256 OID of a specific LFS object in the target repository. OIDs are 256-bit digests — not enumerable and not brute-forceable — and the LFS batch endpoint functions only as an existence oracle, not a listing mechanism. Successful exploitation therefore requires a prior information-disclosure path that exposes OIDs outside the repository boundary. Known paths include public forks that retain stale LFS pointer files in git history, former collaborators who retained object references from a prior `git pull`, and issue or pull request comments that reference pointer file contents.LFS pointer files are committed in plaintext to git history, so anyone who ever cloned or had read access to the target repo retains all OIDs permanently. The attack is effectively a **post-revocation persistence** primitive — after a collaborator loses access, they can continue downloading updated versions of LFS files they previously knew existed.Reproduction Steps**Environment**The issue was reproduced using `gitea/gitea:1.25.5` docker image.**Setup** (performed as victim/admin — represents normal deployment state)**Exploit****Expected output****PoC files**[poc.sh](https://github.com/user-attachments/files/28830752/poc.sh) — end-to-end PoC using real SSH deploy keyRecommended FixA proper fix might require significant architecture change. A short term recommendation is presented below:**Fix 1 — `services/lfs/server.go:267` (defense in depth, immediately effective)**Remove the `LFSObjectAccessible` cross-repo shortcut. Require proof of possession (the normal upload flow) for any object not already linked to the target repo. The JWT is correctly scoped to one `RepoID`; authorization decisions about *other* repos should not be made using the JWT `UserID`.The client will re-upload the bytes (which are hash-verified). 
Performance cost: one redundant upload per cross-repo object. Security gain: the cross-repo trust boundary is enforced regardless of how the JWT was issued.Full patch: [fix1.patch](https://github.com/user-attachments/files/28830753/fix1.patch)**Fix 2 — `routers/private/serv.go:275` (fix the source)**Stop embedding `repo.OwnerID` in the JWT for deploy keys. Options:Add a `DeployKeyID` field to the JWT `Claims` struct; teach `handleLFSToken` to construct a minimal synthetic principal with exactly the deploy key's permissions (single-repo, mode-limited).Or mint a separate JWT type for deploy keys that `server.go` treats as repo-scoped only, refusing to use it for cross-repo operations.Patch provenance: AI-generated + Human-reviewedAttributionThis vulnerability was discovered by Claude, Anthropic's AI assistant, and triaged by Adrian Denkiewicz at Doyensec in collaboration with Anthropic Research.For CVE credits and public acknowledgments: Doyensec in collaboration with Claude and Anthropic Research.
CVSS v3.1 score: 5.4