GHSA-66m4-5jjr-2rg5

## Affected product Gitea — `services/repository/collaboration.go` (`DeleteCollaboration`) + webhook delivery

## Summary When a collaborator with admin permission on a private repo creates a webhook, that webhook keeps firing after the collaborator's access is revoked. Gitea's revocation cleanup `DeleteCollaboration` removes the collaboration record, recalculates accesses, drops watches, and unassigns issues — but it does **not** remove or disable webhooks the user created, and webhook delivery never re-checks whether the creator still has repo access. The former collaborator therefore receives the full payload (issue/comment bodies, commit data) of all future repository events at their controlled endpoint, indefinitely and invisibly.

## Affected code - `services/repository/collaboration.go` → `DeleteCollaboration()` — cleans watches/assignees only; no webhook cleanup. - Webhook delivery path — fires on repo events without re-validating the creator's current access.

## Steps to reproduce Using the provided reproduction materials: 1. Attacker (admin collaborator) creates a webhook → revoke access. 2. Control: `GET /api/v1/repos/admin/wh-repo` (attacker) → **404**. 3. `GET .../hooks` → webhook still `active=true`. 4. Admin creates a new issue **after** revocation → the catcher receives `action:"opened"`, `issue.title:"CRITICAL SECRET: …"`, `issue.body` (sentinel private key), `repository.private:true`. (Runtime-confirmed on `gitea/gitea:1.25.4`. Catcher is an internal sentinel listener; the payload is a planted sentinel, not real data; nothing is sent to any external/metadata endpoint.)

## Impact Authenticated former admin-collaborator → ongoing real-time exfiltration of private content created after revocation; invisible to the owner; scope crosses from the application boundary to data the user should no longer access.

## Suggested remediation 1. On revocation, delete/disable webhooks created by the removed collaborator (or hand them to the owner). 2. Re-validate the creator's current repo access before each webhook delivery. 3. At minimum, warn admins on revocation if the user created webhooks.

## Credit Reported as part of an incomplete-patch / authorization-residue measurement study (responsible disclosure).