CVE-2021-42089
📋 TL;DR
This vulnerability in Zammad's REST API allows unauthorized disclosure of sensitive information. Attackers can access confidential data through API endpoints without proper authentication. Organizations running Zammad versions before 4.1.1 are affected.
💻 Affected Systems
- Zammad
📦 What is this software?
Zammad by Zammad
⚠️ Risk & Real-World Impact
Worst Case
Complete exposure of sensitive customer data, internal communications, authentication tokens, and configuration details leading to data breach, account compromise, and regulatory violations.
Likely Case
Unauthorized access to customer information, support tickets, and internal communications that could be used for social engineering, data theft, or further attacks.
If Mitigated
Limited exposure of non-critical information if proper network segmentation and access controls are implemented, but still represents an information disclosure risk.
🎯 Exploit Status
The vulnerability allows unauthenticated access to sensitive information through REST API endpoints. Exploitation requires only HTTP requests to vulnerable endpoints.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.1.1 and later
Vendor Advisory: https://zammad.com/en/advisories/zaa-2021-13
Restart Required: Yes
Instructions:
1. Backup your Zammad instance. 2. Update to Zammad 4.1.1 or later using your package manager. 3. Restart Zammad services. 4. Verify the update was successful.
🔧 Temporary Workarounds
Network Access Restriction
linuxRestrict access to Zammad REST API endpoints using firewall rules or network segmentation
iptables -A INPUT -p tcp --dport 3000 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -j DROP
Reverse Proxy Authentication
allImplement authentication at reverse proxy level before requests reach Zammad API
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Zammad from untrusted networks
- Deploy a web application firewall (WAF) with rules to block unauthorized API access
🔍 How to Verify
Check if Vulnerable:
Check if Zammad version is below 4.1.1. Attempt to access sensitive API endpoints without authentication to test for information disclosure.Check Version:
zammad versionVerify Fix Applied:
Verify Zammad version is 4.1.1 or higher. Test that sensitive API endpoints now require proper authentication.📡 Detection & Monitoring
Log Indicators:
- Unauthenticated requests to sensitive API endpoints
- Access patterns showing data extraction from multiple endpoints
- Increased API traffic from unusual sources
Network Indicators:
- Unusual volume of GET requests to API endpoints
- Traffic to sensitive endpoints without authentication headers
- Data exfiltration patterns from Zammad API
SIEM Query:
source="zammad" AND (http_method="GET" AND uri_path="/api/*" AND NOT auth_token=*)