CVE-2021-25770
📋 TL;DR
This vulnerability is a server-side template injection (SSTI) in JetBrains YouTrack, allowing attackers to inject malicious templates that can execute arbitrary code on the server. It affects YouTrack instances before version 2020.5.3123, potentially compromising the entire system if exploited. Organizations using vulnerable versions of YouTrack are at risk, especially those with internet-facing deployments.
💻 Affected Systems
- JetBrains YouTrack
📦 What is this software?
Youtrack by Jetbrains
⚠️ Risk & Real-World Impact
Worst Case
Full remote code execution leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Unauthorized access to sensitive data, privilege escalation, or disruption of YouTrack services.
If Mitigated
Limited impact if patched promptly; otherwise, risk remains high due to the critical nature of the vulnerability.
🎯 Exploit Status
SSTI vulnerabilities often have public proof-of-concept exploits, and this one is rated critical with a high CVSS score, making weaponization probable.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2020.5.3123 or later
Vendor Advisory: https://blog.jetbrains.com/blog/2021/02/03/jetbrains-security-bulletin-q4-2020/
Restart Required: Yes
Instructions:
1. Backup your YouTrack data and configuration. 2. Download and install YouTrack version 2020.5.3123 or newer from the JetBrains website. 3. Follow the upgrade instructions provided by JetBrains. 4. Restart the YouTrack service to apply the patch.
🔧 Temporary Workarounds
Network Isolation
allRestrict network access to YouTrack instances to trusted IPs only, reducing exposure to potential attackers.
Use firewall rules (e.g., iptables on Linux or Windows Firewall) to allow only specific IP ranges.
🧯 If You Can't Patch
- Implement strict input validation and sanitization for template inputs in YouTrack configurations.
- Monitor logs and network traffic for unusual activity, and consider temporarily disabling YouTrack if critical.
🔍 How to Verify
Check if Vulnerable:
Check the YouTrack version via the web interface or server logs; if it's below 2020.5.3123, it is vulnerable.Check Version:
On the YouTrack server, run: java -jar youtrack.jar --version or check the admin panel in the web interface.Verify Fix Applied:
After patching, confirm the version is 2020.5.3123 or higher and test for SSTI by attempting safe template injections in a controlled environment.📡 Detection & Monitoring
Log Indicators:
- Unusual template-related errors or unexpected code execution logs in YouTrack application logs.
Network Indicators:
- Suspicious HTTP requests to YouTrack endpoints with template injection payloads.
SIEM Query:
Example: source="youtrack.log" AND ("template injection" OR "SSTI" OR "code execution")