CVE-2025-12756
📋 TL;DR
This vulnerability allows authenticated users with editor permissions in Mattermost Boards to delete comments created by other users, bypassing intended permission checks. It affects Mattermost instances running vulnerable versions where Boards feature is enabled. Attackers need valid editor credentials to exploit this.
💻 Affected Systems
- Mattermost
📦 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
Malicious editor could systematically delete important comments in Boards, disrupting collaboration, erasing evidence, or causing operational confusion in critical projects.
Likely Case
Accidental or intentional deletion of comments by editors who shouldn't have that permission, leading to minor collaboration disruptions and potential data loss.
If Mitigated
Limited impact with proper user role management and audit logging; deleted comments might be recoverable from backups.
🎯 Exploit Status
Exploitation requires valid editor credentials and access to Boards feature.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to Mattermost 11.0.3, 10.12.2, 10.11.5, or 10.5.13
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Backup your Mattermost instance. 2. Download patched version from Mattermost downloads page. 3. Stop Mattermost service. 4. Install updated version. 5. Restart Mattermost service. 6. Verify version is updated.
🔧 Temporary Workarounds
Disable Boards Feature
allTemporarily disable Mattermost Boards feature if not essential
Edit Mattermost config.json: set "EnableBoards" to false
Restrict Editor Permissions
allReview and reduce number of users with editor role in Boards
Use Mattermost System Console > User Management to adjust permissions
🧯 If You Can't Patch
- Implement strict least-privilege access control for editor roles
- Enable comprehensive audit logging for all comment deletion activities
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version via System Console > About or run: mattermost versionCheck Version:
mattermost versionVerify Fix Applied:
After patching, test that editors cannot delete other users' comments in Boards📡 Detection & Monitoring
Log Indicators:
- Unusual pattern of comment deletions by editor users
- Multiple comment deletions in short timeframes
Network Indicators:
- HTTP POST requests to /api/v4/boards/*/comments/*/delete endpoints
SIEM Query:
source="mattermost" AND action="delete_comment" AND user_role="editor"