CVE-2024-23917: JetBrains TeamCity Auth Bypass Vulnerability

CVE-2024-23917 Overview

CVE-2024-23917 is a critical authentication bypass vulnerability in JetBrains TeamCity, a popular continuous integration and continuous deployment (CI/CD) server used by development teams worldwide. This vulnerability allows unauthenticated attackers to bypass authentication mechanisms and achieve remote code execution (RCE) on affected TeamCity servers. Given TeamCity's role in managing build pipelines and deployment processes, successful exploitation could grant attackers access to source code, build artifacts, deployment credentials, and the ability to inject malicious code into software supply chains.

Critical Impact

Unauthenticated attackers can bypass authentication and execute arbitrary code on TeamCity servers, potentially compromising entire software development and deployment pipelines.

Affected Products

• JetBrains TeamCity versions prior to 2023.11.3
• All TeamCity installations exposed to network access without the security patch
• Both on-premises and cloud-hosted TeamCity deployments running vulnerable versions

Discovery Timeline

• 2024-02-06 - CVE-2024-23917 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-23917

Vulnerability Analysis

This authentication bypass vulnerability stems from missing authentication checks (CWE-306) and authentication bypass using an alternate path or channel (CWE-288). The flaw exists in how TeamCity handles certain authentication requests, allowing attackers to circumvent standard authentication mechanisms entirely. Once authentication is bypassed, attackers can leverage TeamCity's powerful features to achieve remote code execution on the underlying server.

TeamCity servers typically have extensive permissions within an organization's infrastructure, including access to version control systems, deployment environments, and sensitive credentials stored for automated deployments. The ability to bypass authentication without any prerequisites makes this vulnerability particularly dangerous for internet-exposed TeamCity instances.

Root Cause

The vulnerability arises from missing authentication controls in specific request handling paths within TeamCity. The application fails to properly enforce authentication for certain endpoints or request patterns, creating an alternate authentication path that attackers can exploit. This represents a fundamental flaw in the access control implementation, allowing attackers to gain administrative access without valid credentials.

The combination of CWE-288 (Authentication Bypass Using an Alternate Path or Channel) and CWE-306 (Missing Authentication for Critical Function) indicates that certain critical functions lack proper authentication gates, and alternative request paths exist that circumvent the intended authentication flow.

Attack Vector

The attack can be executed remotely over the network without requiring any prior authentication, user interaction, or special privileges. An attacker with network access to a vulnerable TeamCity server can craft specific requests to bypass authentication controls. Upon successful bypass, the attacker gains unauthorized access to TeamCity's administrative functions, which can then be leveraged to execute arbitrary code on the server.

The exploitation path typically involves:

1. Identifying a vulnerable TeamCity instance accessible over the network
2. Sending crafted requests that exploit the authentication bypass mechanism
3. Gaining unauthorized administrative access to the TeamCity web interface
4. Leveraging built-in TeamCity features (such as build configurations, custom scripts, or agent commands) to achieve code execution on the server or connected build agents

Due to TeamCity's role in CI/CD pipelines, successful exploitation can lead to supply chain attacks, where malicious code is injected into software builds and distributed to end users.

Detection Methods for CVE-2024-23917

Indicators of Compromise

• Unexpected administrative sessions or user accounts created on TeamCity servers
• Unusual build configurations or modifications to existing build pipelines
• Anomalous authentication logs showing access without valid credentials
• New or modified build steps containing suspicious scripts or commands
• Unexpected network connections from TeamCity servers to external destinations

Detection Strategies

• Monitor TeamCity access logs for authentication anomalies and unauthorized administrative access attempts
• Implement network-level monitoring for unusual traffic patterns to TeamCity servers on ports 8111 (HTTP) or 443 (HTTPS)
• Deploy endpoint detection and response (EDR) solutions like SentinelOne on TeamCity servers to detect post-exploitation activities
• Review TeamCity audit logs for unauthorized configuration changes or new user account creation

Monitoring Recommendations

• Enable comprehensive audit logging within TeamCity and forward logs to a centralized SIEM
• Implement alerting for new administrative user creation or permission changes
• Monitor for unusual process execution on TeamCity servers that may indicate code execution
• Track changes to build configurations and deployment scripts for unauthorized modifications

How to Mitigate CVE-2024-23917

Immediate Actions Required

• Upgrade JetBrains TeamCity to version 2023.11.3 or later immediately
• Restrict network access to TeamCity servers using firewalls and access control lists
• Audit TeamCity instances for any signs of compromise before and after patching
• Review all administrative accounts and remove any unauthorized users
• Inspect recent build configurations and scripts for malicious modifications

Patch Information

JetBrains has released TeamCity version 2023.11.3 which addresses this authentication bypass vulnerability. Organizations should update to this version or later as soon as possible. For detailed information about security issues fixed by JetBrains, refer to the JetBrains Security Issues Fixed page.

Administrators should ensure that all TeamCity instances, including development, staging, and production environments, are updated. After patching, a thorough security audit is recommended to verify no compromise occurred during the vulnerable period.

Workarounds

• If immediate patching is not possible, restrict TeamCity server access to trusted networks only using firewall rules
• Implement additional authentication layers such as VPN requirements or reverse proxy authentication in front of TeamCity
• Disable external network access to TeamCity until the patch can be applied
• Consider temporarily shutting down TeamCity instances exposed to the internet until patching is complete

# Example: Restrict TeamCity access to internal network only using iptables
# Replace 10.0.0.0/8 with your trusted internal network range
iptables -A INPUT -p tcp --dport 8111 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 8111 -j DROP

# Verify TeamCity version after upgrade
cat /path/to/teamcity/BUILD_NUMBER
# Should show 2023.11.3 or later