CVE-2021-42094
📋 TL;DR
CVE-2021-42094 is a command injection vulnerability in Zammad that allows attackers to execute arbitrary commands on the server via custom Packages. This affects all Zammad installations before version 4.1.1 that have Package functionality enabled. Attackers can potentially gain full control of affected systems.
💻 Affected Systems
- Zammad
📦 What is this software?
Zammad by Zammad
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing remote code execution, data theft, lateral movement, and persistent backdoor installation.
Likely Case
Unauthorized command execution leading to data exfiltration, service disruption, or cryptocurrency mining.
If Mitigated
Limited impact with proper network segmentation, minimal privileges, and monitoring in place.
🎯 Exploit Status
Exploitation requires authenticated access to Zammad's Package functionality.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.1.1
Vendor Advisory: https://zammad.com/en/advisories/zaa-2021-18
Restart Required: Yes
Instructions:
1. Backup your Zammad installation and database. 2. Update to Zammad 4.1.1 or later using your package manager or installation method. 3. Restart Zammad services. 4. Verify the update was successful.
🔧 Temporary Workarounds
Disable Package Functionality
allTemporarily disable custom Package installation to prevent exploitation
# Edit Zammad configuration to disable package functionality
# Consult Zammad documentation for specific configuration changes
Network Access Control
linuxRestrict access to Zammad administration interface
# Configure firewall rules to limit access
iptables -A INPUT -p tcp --dport 3000 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Zammad from critical systems
- Enable detailed logging and monitoring for suspicious package-related activities
🔍 How to Verify
Check if Vulnerable:
Check Zammad version via web interface or command line. Versions before 4.1.1 are vulnerable.Check Version:
zammad versionVerify Fix Applied:
Verify Zammad version is 4.1.1 or later and test package functionality with safe test packages.📡 Detection & Monitoring
Log Indicators:
- Unusual package installation attempts
- Suspicious command execution in system logs
- Multiple failed authentication attempts followed by package activity
Network Indicators:
- Unexpected outbound connections from Zammad server
- Traffic to known malicious IPs or domains
SIEM Query:
source="zammad.log" AND ("package install" OR "command execution")