CVE-2020-26030
📋 TL;DR
This vulnerability allows attackers to bypass authentication in Zammad's SSO endpoint by sending a crafted header when SSO is not configured. Attackers can create authenticated sessions to perform any actions as other users. All Zammad instances running vulnerable versions are affected.
💻 Affected Systems
- Zammad
📦 What is this software?
Zammad by Zammad
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise where attackers gain administrative privileges, access sensitive customer data, modify configurations, and perform destructive actions across the entire Zammad instance.
Likely Case
Unauthorized access to customer support tickets, user data, and system settings, potentially leading to data theft, privilege escalation, and service disruption.
If Mitigated
Limited impact with proper network segmentation, monitoring, and access controls that detect and block unauthorized authentication attempts.
🎯 Exploit Status
Exploitation requires sending a crafted header to the SSO endpoint, which is straightforward for attackers with basic HTTP manipulation skills.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.4.1 and later
Vendor Advisory: https://zammad.com/news/security-advisory-zaa-2020-18
Restart Required: Yes
Instructions:
1. Backup your Zammad instance and database. 2. Update to Zammad 3.4.1 or later using your package manager or deployment method. 3. Restart the Zammad service. 4. Verify the update was successful.
🔧 Temporary Workarounds
Disable SSO endpoint
allTemporarily disable or block access to the SSO endpoint if not in use
# Configure web server (nginx example) to block /auth/sso
location /auth/sso { deny all; }
# Configure firewall to block access to SSO endpoint
Enable SSO configuration
allConfigure SSO properly with authentication requirements
# Configure Zammad SSO according to documentation
# See: https://docs.zammad.org/en/latest/system/sso.html
🧯 If You Can't Patch
- Implement network-level restrictions to limit access to the SSO endpoint only to trusted sources
- Enable detailed logging and monitoring for authentication attempts and session creation events
🔍 How to Verify
Check if Vulnerable:
Check Zammad version: if running version < 3.4.1 and SSO is not configured, the system is vulnerable.Check Version:
zammad run rails r "puts Zammad::Application::Version"Verify Fix Applied:
Verify Zammad version is 3.4.1 or later and test that unauthorized SSO authentication attempts are properly rejected.📡 Detection & Monitoring
Log Indicators:
- Unusual authentication attempts to /auth/sso endpoint
- Session creation without proper authentication flow
- Multiple failed SSO attempts followed by successful authentication
Network Indicators:
- HTTP requests to /auth/sso with crafted headers
- Unusual traffic patterns to authentication endpoints
SIEM Query:
source="zammad.log" AND (uri_path="/auth/sso" AND NOT user_agent="browser-agent")