CVE-2021-37544
📋 TL;DR
CVE-2021-37544 is an insecure deserialization vulnerability in JetBrains TeamCity that allows remote attackers to execute arbitrary code on affected servers. This affects TeamCity installations before version 2020.2.4. Organizations using vulnerable TeamCity versions for CI/CD pipelines are at risk.
💻 Affected Systems
- JetBrains TeamCity
📦 What is this software?
Teamcity by Jetbrains
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the TeamCity server leading to full system takeover, data exfiltration, and lateral movement within the network.
Likely Case
Remote code execution allowing attackers to steal credentials, modify build processes, inject malicious code into software artifacts, or disrupt CI/CD operations.
If Mitigated
Limited impact if proper network segmentation, least privilege access, and monitoring are in place, though the vulnerability still presents significant risk.
🎯 Exploit Status
Exploitation requires authentication but is relatively straightforward once access is obtained. The vulnerability is in the deserialization process of certain data structures.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2020.2.4 or later
Vendor Advisory: https://blog.jetbrains.com/blog/2021/08/05/jetbrains-security-bulletin-q2-2021/
Restart Required: Yes
Instructions:
1. Backup TeamCity configuration and data. 2. Download TeamCity 2020.2.4 or later from JetBrains. 3. Stop TeamCity service. 4. Install the new version following JetBrains upgrade documentation. 5. Restart TeamCity service. 6. Verify functionality.
🔧 Temporary Workarounds
Network Access Restriction
allRestrict network access to TeamCity servers to only trusted IP addresses and networks.
Use firewall rules to limit inbound connections to TeamCity ports (default 8111)
Authentication Hardening
allImplement strong authentication controls and monitor for suspicious login attempts.
Enable MFA, enforce strong password policies, implement account lockout policies
🧯 If You Can't Patch
- Isolate TeamCity servers in a dedicated network segment with strict access controls
- Implement application-level monitoring and alerting for suspicious deserialization activities
🔍 How to Verify
Check if Vulnerable:
Check TeamCity version in Administration → Server Administration → Server Health → VersionCheck Version:
On TeamCity server: cat /opt/teamcity/version.txt (Linux) or check TeamCity web interfaceVerify Fix Applied:
Verify version is 2020.2.4 or later and test deserialization-related functionality📡 Detection & Monitoring
Log Indicators:
- Unusual deserialization errors in TeamCity logs
- Suspicious Java serialization payloads in request logs
- Unexpected process execution from TeamCity service account
Network Indicators:
- Unusual outbound connections from TeamCity server
- Large serialized data transfers to/from TeamCity
SIEM Query:
source="teamcity.log" AND ("deserialization" OR "serialization" OR "java.io") AND (error OR exception OR warning)