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This vulnerability, an Insecure Direct Object Reference (IDOR) combined with an authentication bypass, exists within the Boards feature of Mattermost. The application endpoints responsible for retrieving attached files and for handling block subscriptions fail to validate if the authenticated user has appropriate ‘read’ or ‘subscribe’ permissions for the target board. When a user makes a request, the system checks only that the user is logged in but does not verify the board membership or permissions associated with the provided board ID or block ID. An attacker can exploit this by manually changing the ‘boardId’ parameter in API requests (e.g., /api/v1/boards/{boardId}/files/{fileId}) or the ‘blockId’ for subscription endpoints to reference boards they do not have access to. The server processes these requests without the necessary authorization check, leading to unauthorized access to sensitive files and the ability to receive live updates from private boards, effectively bypassing all intended board-level access controls.
Platform: Mattermost
Version: 10.11.0 to 10.11.4, 10.5.0 to 10.5.12
Vulnerability: Authentication Bypass
Severity: Critical
Date: 2025
Prediction: 2025-03-15
What Undercode Say:
curl -H “Authorization: Bearer $TOKEN” “https://target.com/api/v1/boards/PRIVATE_BOARD_ID/files/FILE_ID”
curl -X POST -H “Authorization: Bearer $TOKEN” -H “Content-Type: application/json” -d ‘{“blockId”:”PRIVATE_BLOCK_ID”}’ “https://target.com/api/v1/subscribe”
How Exploit:
1. Attacker obtains a valid authentication token.
2. Attacker enumerates or guesses board/block IDs.
- Attacker sends crafted API requests to file access or subscription endpoints with unauthorized IDs.
- Server returns confidential data or establishes unauthorized subscription due to missing permission check.
Protection from this CVE:
Update to Mattermost versions patching CVE-2025-XXXX. Implement mandatory authorization checks on all file and subscription endpoints. Apply principle of least privilege.
Impact:
Unauthorized access to confidential board files. Unauthorized real-time subscription to private board updates. Data breach and information disclosure.
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Sources:
Reported By: github.com
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