CVE-2021-39172
📋 TL;DR
CVE-2021-39172 is a critical newline injection vulnerability in Cachet status page systems that allows authenticated users (both regular users and admins) to inject malicious configuration values leading to arbitrary code execution on the server. This affects all Cachet installations prior to version 2.5.1. Attackers can gain full control of affected servers through configuration manipulation.
💻 Affected Systems
- Cachet
📦 What is this software?
Catchet by Catchethq
⚠️ Risk & Real-World Impact
Worst Case
Complete server compromise allowing attackers to execute arbitrary code, steal data, deploy ransomware, pivot to other systems, and maintain persistent access.
Likely Case
Server takeover leading to data theft, defacement of status pages, cryptocurrency mining, or use as part of botnets.
If Mitigated
Limited impact with proper network segmentation and access controls, potentially only affecting the Cachet application itself.
🎯 Exploit Status
Exploitation requires authenticated access but is straightforward once credentials are obtained. Public technical details available in SonarSource blog post.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.5.1
Vendor Advisory: https://github.com/fiveai/Cachet/security/advisories/GHSA-9jxw-cfrh-jxq6
Restart Required: Yes
Instructions:
1. Backup your Cachet database and configuration. 2. Update Cachet to version 2.5.1 or later. 3. Restart the web server and Cachet services. 4. Verify the update was successful.
🔧 Temporary Workarounds
Restrict Admin Dashboard Access
allLimit access to Cachet administration dashboard to trusted source IP addresses only
# Configure web server (nginx example)
location /admin { allow 192.168.1.0/24; deny all; }
# Configure web server (Apache example)
<Location /admin> Order Deny,Allow Deny from all Allow from 192.168.1.0/24 </Location>
🧯 If You Can't Patch
- Implement strict network access controls to limit Cachet admin interface to trusted IP addresses only
- Monitor for suspicious configuration changes and newline characters in configuration update requests
🔍 How to Verify
Check if Vulnerable:
Check Cachet version in admin dashboard or via composer show cachethq/cachet commandCheck Version:
composer show cachethq/cachet | grep versionsVerify Fix Applied:
Verify version is 2.5.1 or higher and test that newline characters are rejected in configuration fields📡 Detection & Monitoring
Log Indicators:
- Unusual configuration update requests containing newline characters
- Multiple failed login attempts followed by configuration changes
- PHP execution errors or unusual process spawns
Network Indicators:
- HTTP POST requests to /admin/settings containing newline characters in parameters
- Unusual outbound connections from Cachet server
SIEM Query:
source="cachet_logs" AND (message="*\n*" OR message="*\r*" OR message="*newline*") AND uri="/admin/settings"🔗 References
- https://blog.sonarsource.com/cachet-code-execution-via-laravel-configuration-injection/
- https://github.com/fiveai/Cachet/releases/tag/v2.5.1
- https://github.com/fiveai/Cachet/security/advisories/GHSA-9jxw-cfrh-jxq6
- https://blog.sonarsource.com/cachet-code-execution-via-laravel-configuration-injection/
- https://github.com/fiveai/Cachet/releases/tag/v2.5.1
- https://github.com/fiveai/Cachet/security/advisories/GHSA-9jxw-cfrh-jxq6
