CVE-2025-13870
📋 TL;DR
This vulnerability in Mattermost allows authenticated users to access files and subscribe to blocks in Boards they shouldn't have permission to view. It affects Mattermost instances running vulnerable versions where the Boards feature is enabled. Attackers need valid user credentials but can then bypass intended access controls.
💻 Affected Systems
- Mattermost
📦 What is this software?
Mattermost Server by Mattermost
Mattermost Server by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
An authenticated malicious insider or compromised account could access sensitive files and board content across the organization, potentially exposing confidential information, intellectual property, or private communications.
Likely Case
Accidental or intentional unauthorized access to board files and subscriptions, leading to information disclosure and potential data leakage within the organization.
If Mitigated
Limited impact due to existing network segmentation, strong authentication controls, and monitoring of board access patterns.
🎯 Exploit Status
Exploitation requires authenticated access but the vulnerability itself is straightforward - the system fails to validate permissions when accessing board files and subscriptions.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 10.11.5 and 10.5.13
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Backup your Mattermost instance. 2. Download and install Mattermost version 10.11.5 or 10.5.13 from the official website. 3. Follow the Mattermost upgrade documentation for your deployment type. 4. Restart the Mattermost service.
🔧 Temporary Workarounds
Disable Boards Feature
allTemporarily disable the Boards feature to prevent exploitation while planning upgrade
Edit config.json: set 'EnableBoards' to false
Restart Mattermost service
🧯 If You Can't Patch
- Implement strict access controls and monitoring for authenticated users accessing board resources
- Segment Mattermost instance from sensitive networks and implement additional authentication layers
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version via System Console > About or run: SELECT * FROM Systems WHERE Name = 'Version'Check Version:
SELECT * FROM Systems WHERE Name = 'Version'Verify Fix Applied:
Verify version is 10.11.5 or higher, or 10.5.13 or higher, and test that authenticated users cannot access board files/subscriptions without proper permissions📡 Detection & Monitoring
Log Indicators:
- Unusual access patterns to board files from users
- Multiple failed permission checks followed by successful access
- User accessing board IDs outside their normal scope
Network Indicators:
- Increased API calls to board file endpoints
- Unusual patterns in board subscription requests
SIEM Query:
source="mattermost" AND (event="board_file_access" OR event="board_subscribe") | stats count by user, board_id