CVE-2025-55070
📋 TL;DR
Mattermost versions before 11 fail to enforce multi-factor authentication on WebSocket connections, allowing unauthenticated users to bypass MFA and access sensitive information via WebSocket events. This affects all Mattermost deployments using MFA with versions below 11.
💻 Affected Systems
- Mattermost
📦 What is this software?
Mattermost Server by Mattermost
⚠️ Risk & Real-World Impact
Worst Case
Unauthenticated attackers could access sensitive channel data, private messages, and user information without MFA verification, potentially leading to data breaches.
Likely Case
Attackers with network access could bypass MFA to read messages and access channels they shouldn't have access to, violating confidentiality.
If Mitigated
With proper network segmentation and access controls, impact is limited to authorized network segments only.
🎯 Exploit Status
Exploitation involves establishing WebSocket connections without proper MFA validation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 11.0.0 or later
Vendor Advisory: https://mattermost.com/security-updates
Restart Required: Yes
Instructions:
1. Backup Mattermost data and configuration. 2. Download Mattermost version 11.0.0 or later. 3. Stop Mattermost service. 4. Replace existing installation with new version. 5. Restart Mattermost service. 6. Verify upgrade completed successfully.
🔧 Temporary Workarounds
Disable WebSocket connections
allTemporarily disable WebSocket connections to prevent exploitation while patching.
Edit config.json: set 'EnableWebSocket' to false
Restart Mattermost service
Network segmentation
linuxRestrict access to Mattermost WebSocket port (default 443/80) to trusted networks only.
firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="TRUSTED_NETWORK" port protocol="tcp" port="443" accept'
firewall-cmd --reload
🧯 If You Can't Patch
- Implement strict network access controls to limit WebSocket connections to trusted IPs only.
- Disable MFA temporarily if business impact is acceptable, then re-enable after patching.
🔍 How to Verify
Check if Vulnerable:
Check Mattermost version via web interface Admin Console > System Console > About, or run: mattermost versionCheck Version:
mattermost versionVerify Fix Applied:
Verify version is 11.0.0 or higher and test that WebSocket connections require MFA authentication.📡 Detection & Monitoring
Log Indicators:
- WebSocket connections without MFA validation in logs
- Unauthenticated WebSocket handshake attempts
Network Indicators:
- WebSocket traffic to Mattermost without preceding MFA authentication
- Unusual WebSocket connection patterns
SIEM Query:
source="mattermost.log" AND "WebSocket" AND NOT "MFA"