CVE-2025-20051
📋 TL;DR
This vulnerability in Mattermost Boards allows authenticated users to read arbitrary files on the server by duplicating specially crafted blocks. It affects Mattermost instances running vulnerable versions of the Boards feature, potentially exposing sensitive system files and configuration data.
💻 Affected Systems
- Mattermost Boards
📦 What is this software?
Mattermost Server by Mattermost
Mattermost Server by Mattermost
Mattermost Server by Mattermost
Mattermost Server by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
Attackers could read sensitive system files including configuration files, SSH keys, database credentials, and other secrets, leading to complete system compromise.
Likely Case
Authenticated users exploit the vulnerability to read sensitive files, potentially accessing credentials, configuration data, or other restricted information.
If Mitigated
With proper network segmentation and file system permissions, impact is limited to files accessible by the Mattermost process user.
🎯 Exploit Status
Requires authenticated user access to create/duplicate boards
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Mattermost versions 10.4.2, 9.11.8, 10.3.3, 10.2.3 and later
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Backup your Mattermost instance. 2. Upgrade to patched version (10.4.2, 9.11.8, 10.3.3, or 10.2.3). 3. Restart Mattermost service. 4. Verify upgrade completed successfully.
🔧 Temporary Workarounds
Disable Boards Feature
allTemporarily disable the Boards feature if not essential
Edit config.json: set "EnableBoards" to false
Restart Mattermost service
Restrict Board Permissions
allLimit board creation/duplication to trusted administrators only
Configure board permissions via System Console > Boards
🧯 If You Can't Patch
- Implement strict file system permissions to limit Mattermost process access
- Deploy network segmentation to isolate Mattermost from sensitive systems
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version via System Console > About or run: mattermost versionCheck Version:
mattermost versionVerify Fix Applied:
Verify version is 10.4.2, 9.11.8, 10.3.3, 10.2.3 or later📡 Detection & Monitoring
Log Indicators:
- Unusual board duplication activity
- Multiple file read errors in logs
- Suspicious board creation patterns
Network Indicators:
- Unusual outbound file transfers from Mattermost server
SIEM Query:
source="mattermost.log" AND ("board duplicate" OR "file read error")