CVE-2019-20853
📋 TL;DR
Mattermost Packages before version 5.16.3 contain a vulnerability that could allow internet access to a service with remote code execution capabilities. This affects organizations running vulnerable Mattermost deployments, potentially exposing them to complete system compromise.
💻 Affected Systems
- Mattermost Packages
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise allowing attackers to execute arbitrary code, steal sensitive data, deploy ransomware, or pivot to other network resources.
Likely Case
Unauthorized access to the Mattermost server leading to data exfiltration, privilege escalation, or deployment of backdoors.
If Mitigated
Limited impact with proper network segmentation and access controls preventing external exploitation.
🎯 Exploit Status
The description suggests internet access could lead to RCE, indicating potential for unauthenticated exploitation with low complexity.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.16.3 and later
Vendor Advisory: https://mattermost.com/security-updates/
Restart Required: Yes
Instructions:
1. Backup your Mattermost data and configuration. 2. Upgrade to Mattermost version 5.16.3 or later. 3. Restart the Mattermost service. 4. Verify the upgrade was successful.
🔧 Temporary Workarounds
Network Segmentation
linuxRestrict network access to the Mattermost service to only trusted IP addresses or internal networks.
# Use firewall rules to restrict access
# Example for iptables:
iptables -A INPUT -p tcp --dport 8065 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 8065 -j DROP
Service Isolation
linuxRun Mattermost in a container or VM with limited privileges and network access.
# Example Docker run command with network restrictions
docker run --network isolated_network --cap-drop=ALL mattermost/mattermost-prod-app
🧯 If You Can't Patch
- Implement strict network access controls to prevent external access to the Mattermost service
- Deploy intrusion detection systems and monitor for unusual activity on Mattermost servers
🔍 How to Verify
Check if Vulnerable:
Check the Mattermost version in System Console > About Mattermost or run: grep 'Version' /opt/mattermost/config/config.jsonCheck Version:
grep 'Version' /opt/mattermost/config/config.json || mattermost versionVerify Fix Applied:
Confirm version is 5.16.3 or higher in System Console > About Mattermost📡 Detection & Monitoring
Log Indicators:
- Unusual process execution from Mattermost service
- Unexpected network connections from Mattermost server
- Authentication failures or unusual user activity
Network Indicators:
- Unexpected outbound connections from Mattermost server
- Traffic to suspicious external IPs on non-standard ports
SIEM Query:
source="mattermost.logs" AND (process_execution OR network_connection) | stats count by src_ip, dest_ip, process_name