CVE-2026-27775: Gitea: Cached Per-Branch Permission Check in Pre-Receive Hook Allows Full Repository Write

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.