CVE-2024-27198

CVE-2024-27198: Critical Authentication Bypass in JetBrains TeamCity

AI-generated analysis based on the vulnerability data on this page.

Summary

JetBrains TeamCity, a widely-used continuous integration and continuous deployment (CI/CD) server, contains a critical authentication bypass vulnerability in versions prior to 2023.11.4. An unauthenticated remote attacker can exploit this flaw to perform administrative actions on the server, effectively gaining full control over the CI/CD pipeline. This vulnerability carries a CVSS v3 score of 9.8 and has been actively exploited in the wild since early March 2024.

Background

TeamCity is a popular CI/CD platform developed by JetBrains, used by organizations worldwide to automate build, test, and deployment workflows. Because CI/CD servers typically hold privileged access to source code repositories, build artifacts, secrets, and deployment credentials, they represent high-value targets in enterprise environments. A successful compromise of a TeamCity server can lead to supply chain attacks, source code theft, and unauthorized deployment of malicious artifacts.

Root Cause

The vulnerability is classified under CWE-288. The underlying issue stems from an authentication logic flaw in TeamCity's web interface that allows an attacker to access administrative endpoints without presenting valid credentials. The specific implementation defect creates an alternate path to privileged functionality that bypasses the standard authentication and authorization checks entirely.

Impact

With a CVSS v3 score of 9.8 (Critical) and the vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, this vulnerability is network-exploitable, requires no privileges, no user interaction, and provides complete compromise of the CIA triad:

• Confidentiality: HIGH — Attackers can access build configurations, source code, secrets, and credentials stored within the TeamCity environment.
• Integrity: HIGH — Attackers can modify build pipelines, inject malicious code into build artifacts, or alter deployment configurations.
• Availability: HIGH — Attackers can disrupt CI/CD operations, delete projects, or render the server unusable.

Given that CI/CD infrastructure often sits at the heart of software supply chains, the downstream impact can extend far beyond the TeamCity instance itself.

Exploitation Walkthrough

Ethics & Legal Notice: This section describes the vulnerability mechanism from a defensive perspective only. Attempting to exploit systems without explicit authorization is illegal and unethical. The information below is intended to help defenders understand the attack surface and implement effective protections.

The exploitation of this vulnerability typically follows this pattern:

1. Reconnaissance: The attacker identifies a publicly accessible TeamCity instance, often through internet scanning or by targeting known organizational CI/CD infrastructure.
2. Bypass Attempt: The attacker sends a specially crafted HTTP request to an administrative endpoint, leveraging the authentication bypass flaw to access the endpoint without credentials.
3. Administrative Action: Once authenticated as an administrative user, the attacker can create new projects, modify existing build configurations, extract stored secrets, or deploy malicious build agents.
4. Persistence & Lateral Movement: With administrative access, the attacker may establish persistent access mechanisms, such as creating rogue user accounts, installing malicious plugins, or exfiltrating credentials to move laterally within the target environment.

Mass exploitation of this vulnerability was observed in the wild beginning March 2024, with attackers rapidly deploying automated exploitation tools against exposed TeamCity instances.

Affected and Patched Versions

Organizations running TeamCity versions older than 2023.11.4 should assume they are vulnerable and, if internet-facing, potentially compromised.

Remediation

1. Upgrade Immediately: Apply JetBrains TeamCity version 2023.11.4 or later as soon as possible. JetBrains has released patches addressing this authentication bypass.
2. Network Segmentation: Restrict network access to TeamCity administrative interfaces to authorized internal IP ranges only. Do not expose TeamCity directly to the internet unless absolutely necessary.
3. Reverse Proxy & WAF: Place TeamCity behind a reverse proxy with Web Application Firewall (WAF) rules that can detect and block anomalous requests to administrative endpoints.
4. Credential Rotation: After patching, rotate all credentials, API keys, and secrets stored within the TeamCity environment, as they may have been compromised during the exposure window.
5. Audit Build Pipelines: Review recent build history and configuration changes for unauthorized modifications, new projects, or unexpected build agent registrations.

Detection

Defenders should monitor for the following indicators:

• Unusual HTTP requests to administrative endpoints from unknown IP addresses without prior authentication.
• New administrative user accounts or API tokens created outside of normal change management windows.
• Unexpected build agent registrations or connections from unauthorized hosts.
• Anomalous build executions or configuration modifications in TeamCity audit logs.
• Network scans targeting TeamCity default ports from suspicious IP ranges.

Assessment

This vulnerability represents a textbook example of why internet-facing CI/CD infrastructure is a critical attack surface. With an EPSS score of 0.99938 (99.94th percentile), the probability of exploitation is virtually certain for exposed instances. The inclusion in CISA's Known Exploited Vulnerabilities catalog and the EU's exploited vulnerability database confirms that threat actors are actively and successfully targeting this flaw.

Key lessons:

1. Authentication is a non-negotiable boundary. A single bypass flaw in authentication logic can collapse an entire security model, especially for systems that gate access to production pipelines and secrets.
2. Patch velocity matters. The window between disclosure and mass exploitation was extremely narrow. Organizations with exposed CI/CD infrastructure must have emergency patching procedures that can operate on hours, not days.

References

• https://www.darkreading.com/cyberattacks-data-breaches/jetbrains-teamcity-mass-exploitation-underway-rogue-accounts-thrive
• https://www.jetbrains.com/privacy-security/issues-fixed/
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-27198