CVE-2021-31910
📋 TL;DR
This CVE describes a Server-Side Request Forgery (SSRF) vulnerability in JetBrains TeamCity that allows attackers to make unauthorized requests from the server to internal systems. It affects TeamCity installations before version 2020.2.3, potentially exposing sensitive internal network information to attackers.
💻 Affected Systems
- JetBrains TeamCity
📦 What is this software?
Teamcity by Jetbrains
⚠️ Risk & Real-World Impact
Worst Case
Attackers could access internal services, retrieve sensitive data, or pivot to other systems within the network environment.
Likely Case
Information disclosure of internal network resources, potentially exposing configuration data or credentials.
If Mitigated
Limited impact with proper network segmentation and access controls in place.
🎯 Exploit Status
SSRF vulnerabilities are commonly exploited and require some level of access to the TeamCity interface.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2020.2.3 or later
Vendor Advisory: https://blog.jetbrains.com/blog/2021/05/07/jetbrains-security-bulletin-q1-2021/
Restart Required: Yes
Instructions:
1. Backup TeamCity configuration and data. 2. Download TeamCity 2020.2.3 or later from JetBrains. 3. Stop TeamCity service. 4. Install the updated version. 5. Restart TeamCity service. 6. Verify functionality.
🔧 Temporary Workarounds
Network Segmentation
allRestrict TeamCity server's outbound network access to only necessary services
Access Control
allImplement strict authentication and authorization controls for TeamCity access
🧯 If You Can't Patch
- Implement strict network segmentation to limit TeamCity server's outbound connections
- Monitor TeamCity logs for unusual outbound requests and implement WAF rules to block SSRF patterns
🔍 How to Verify
Check if Vulnerable:
Check TeamCity version in Administration → Server Administration → Server InformationCheck Version:
Check TeamCity web interface at Administration → Server Administration → Server InformationVerify Fix Applied:
Confirm version is 2020.2.3 or later in Administration → Server Administration → Server Information📡 Detection & Monitoring
Log Indicators:
- Unusual outbound HTTP requests from TeamCity server
- Requests to internal IP addresses or services
Network Indicators:
- TeamCity server making unexpected outbound connections
- Requests to internal network segments from TeamCity
SIEM Query:
source="teamcity" AND (url="http://internal*" OR url="https://internal*")