Gitea: Notification API leaks private issue metadata after access revocation
# Summary
An information disclosure issue in the Gitea Notification API allows users who have lost access to a private repository to continue accessing private issue or pull request information through existing notification threads. Although repository information is hidden after access revocation, the subject field remains accessible and continues to expose private metadata.
# Details
CVE-2026-20800 was fixed in v1.25.4 to prevent users from accessing private repository information through notification APIs after their repository access had been revoked.
During testing on Gitea v1.26.2, the repository field in NotificationThread responses is correctly set to null after access revocation. However, the associated subject field remains available.
The exposed subject object may contain:
- Private issue or pull request titles
- Repository-related API and HTML URLs
- Issue or pull request state
- Latest comment URLs and comment identifiers
Additionally, the exposed notification data is not limited to historical information. If new comments are added to the issue or pull request while the notification remains unread, fields such as latest_comment_url and updated_at continue to change. As a result, a user whose repository access has been revoked can still observe ongoing issue or pull request activity through notification APIs.
The observed behavior suggests that access control is applied to the repository field but not consistently applied to the associated subject information.
# PoC
Environment
- Gitea v1.26.2
- Private repository
Steps to Reproduce
1. User sun creates a private repository and grants read access to user li.
2. User li subscribes to repository notifications.
3. User sun creates a private issue and adds a comment.
4. User li receives a notification (thread_id = 14).
5. User sun revokes li's repository access.
6. User li requests:
```http
GET /api/v1/repos/sun/{repo}/issues/1
```
Response:
```text
404 Not Found
```
7. User li requests:
```http
GET /api/v1/notifications?all=true
```
8. User li requests:
```http
GET /api/v1/notifications/threads/14
```
Observed Result
The notification is returned successfully. The repository field is null, but the subject field still contains private issue metadata.
Example:
```json
{
"id": 14,
"repository": null,
"subject": {
"title": "private issue title",
"url": "http://localhost:3000/api/v1/repos/sun/private-repo/issues/1",
"latest_comment_url": "http://localhost:3000/api/v1/repos/sun/private-repo/issues/comments/24",
"html_url": "http://localhost:3000/sun/private-repo/issues/1",
"state": "open"
}
}
```
Expected Result
Users who no longer have access to a repository should not receive private issue or pull request information through notification APIs. The subject field should be removed, redacted, or otherwise protected by the same access controls applied to the repository field.
Detailed PoC
https://anonymous.4open.science/r/Gitea_PoC-EC93/1_poc_notification_leak
# Impact
Affected Endpoints
GET /api/v1/notificationsGET /api/v1/notifications/threads/{id}
Prerequisites
- The user previously had legitimate access to the private repository.
- The notification was received before repository access was revoked.
Impact
- Disclosure of private issue or pull request titles.
- Disclosure of repository information through notification URLs.
- Disclosure of issue or pull request state.
- Disclosure of comment activity metadata.
- Continued visibility into issue or pull request activity after repository access has been revoked.
Tested Version
