CVE-2024-27198: JetBrains TeamCity Auth Bypass Vulnerability

CVE-2024-27198 Overview

CVE-2024-27198 is a critical authentication bypass vulnerability in JetBrains TeamCity, a popular continuous integration and continuous delivery (CI/CD) server used by development teams worldwide. This vulnerability allows unauthenticated remote attackers to bypass authentication mechanisms and perform administrative actions on affected TeamCity instances. Given TeamCity's role in software development pipelines, successful exploitation could lead to supply chain compromises, source code theft, and deployment of malicious code through compromised build processes.

Critical Impact

This vulnerability enables complete administrative control of TeamCity servers without authentication, potentially compromising entire CI/CD pipelines and enabling supply chain attacks.

Affected Products

• JetBrains TeamCity versions prior to 2023.11.4
• All JetBrains TeamCity installations accessible over the network
• Self-hosted TeamCity deployments with default configurations

Discovery Timeline

• 2024-03-04 - CVE-2024-27198 published to NVD
• 2025-10-24 - Last updated in NVD database

Technical Details for CVE-2024-27198

Vulnerability Analysis

This authentication bypass vulnerability (CWE-288: Authentication Bypass Using an Alternate Path or Channel) allows attackers to circumvent normal authentication controls in JetBrains TeamCity. The flaw enables unauthenticated users to access administrative functionality that should require proper authentication credentials. Once exploited, attackers gain the ability to create new administrator accounts, modify build configurations, access sensitive project data, and potentially inject malicious code into software builds.

The vulnerability is particularly dangerous in CI/CD environments where TeamCity manages automated build and deployment processes. Attackers exploiting this flaw can manipulate the software supply chain by modifying build scripts, injecting backdoors into compiled artifacts, or exfiltrating sensitive credentials stored within the build system.

Root Cause

The root cause lies in improper authentication validation within TeamCity's request handling mechanism. The application fails to properly enforce authentication requirements for certain administrative endpoints, allowing requests to bypass the normal authentication flow through an alternate path. This authentication bypass using an alternate channel (CWE-288) means that even with authentication mechanisms in place, certain requests can circumvent these controls entirely.

Attack Vector

The attack is network-based and requires no privileges or user interaction. Attackers can exploit this vulnerability remotely against any TeamCity instance exposed to the network. The exploitation flow typically involves:

1. Identifying exposed TeamCity instances through network scanning
2. Crafting requests that bypass authentication mechanisms
3. Creating rogue administrator accounts for persistent access
4. Leveraging administrative access to compromise build configurations and deployment pipelines

The vulnerability has been actively exploited in the wild, with mass exploitation campaigns observed creating unauthorized administrator accounts on vulnerable instances. According to Dark Reading analysis, attackers have leveraged this vulnerability to establish persistent access through rogue accounts.

Detection Methods for CVE-2024-27198

Indicators of Compromise

• Unexpected administrator accounts created in TeamCity without legitimate authorization
• Unusual login activity or API calls from unfamiliar IP addresses
• Modified build configurations or newly created build jobs without authorized changes
• Suspicious network traffic to TeamCity administrative endpoints from external sources

Detection Strategies

• Monitor TeamCity audit logs for unauthorized user creation events, especially administrator accounts
• Implement network monitoring to detect anomalous access patterns to TeamCity servers
• Deploy web application firewalls (WAF) rules to detect exploitation attempts targeting authentication bypass patterns
• Utilize endpoint detection tools to identify post-exploitation activities on TeamCity servers

Monitoring Recommendations

• Enable comprehensive audit logging in TeamCity and forward logs to a SIEM solution
• Establish baseline behavior for TeamCity administrative activities and alert on deviations
• Monitor for unexpected changes to build configurations, credentials, or system settings
• Implement alerting for new user account creation, particularly those with administrative privileges

How to Mitigate CVE-2024-27198

Immediate Actions Required

• Upgrade JetBrains TeamCity to version 2023.11.4 or later immediately
• Audit all user accounts in TeamCity and remove any unauthorized administrator accounts
• Review recent audit logs for signs of unauthorized access or configuration changes
• Restrict network access to TeamCity instances using firewall rules until patching is complete
• If exposure is suspected, rotate all credentials and API tokens stored in TeamCity

Patch Information

JetBrains has released TeamCity version 2023.11.4 that addresses this vulnerability. Organizations should prioritize this update given the active exploitation and critical severity. The patch is available through the JetBrains Security Issues Fixed page. This vulnerability is listed in the CISA Known Exploited Vulnerabilities Catalog, mandating federal agencies to remediate within specified timeframes.

Workarounds

• Implement network segmentation to limit TeamCity access to trusted internal networks only
• Place TeamCity behind a VPN or reverse proxy with additional authentication requirements
• Enable multi-factor authentication for all TeamCity user accounts where supported
• Monitor and restrict outbound network connections from TeamCity servers to detect potential data exfiltration

# Network access restriction example using iptables
# Restrict TeamCity web interface to internal network only
iptables -A INPUT -p tcp --dport 8111 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 8111 -s 192.168.0.0/16 -j ACCEPT
iptables -A INPUT -p tcp --dport 8111 -j DROP