GHSA-649p-mmhf-85c7: Gitea: Cached Per-Branch Permission Check in Pre-Receive Hook Allows Full Repository Write

Vulnerability Header | Field | Value | | ------------------- | ----------------------------------------------------------------------------------- | | Vulnerability Title | Cached Per-Branch Permission Check in Pre-Receive Hook Allows Full Repository Write | | Severity Rating | High | | Bug Category | Authorization Bypass | | Location | routers/private/hook_pre_receive.go:55-64, CanWriteCode() | | Affected Versions | 1.25.5 | Executive Summary The pre-receive hook in Gitea evaluates the CanMaintainerWriteToBranch permission only once per git push session and caches the result for all subsequent refs in the same batch. An attacker who has a legitimate per-branch write grant (e.g., via an open pull request with "Allow edits from maintainers" enabled) can batch-push that branch together with any other ref. The cached true from the first ref is reused for all following refs, allowing the attacker to overwrite protected branches (including main), create arbitrary new branches, and push tags. This effectively escalates a single-branch maintainer-edit grant into full repository write access. Root Cause Analysis Technical Description When processing a multi-ref git push, the HookPreReceive handler at hook_pre_receive.go:107 iterates over all incoming refs. For each branch ref, preReceiveBranch (:140) updates ctx.branchName to the current branch (:142) and then calls AssertCanWriteCode() (:144). CanWriteCode() (:55-64) checks whether the user can write to the repository. On the first call, it evaluates issues_model.CanMaintainerWriteToBranch(ctx, userPerm, ctx.branchName, user) and stores the result in a boolean flag (canWriteCode) with a guard (checkedCanWriteCode). On all subsequent calls within the same batch, it returns the cached boolean without re-evaluating against the now-different ctx.branchName. This means the permission check is branch-specific in its inputs but session-scoped in its caching — a classic check-vs-use divergence. A second contributing facto