CVE-2025-24459: JetBrains TeamCity XSS Vulnerability

CVE-2025-24459 Overview

CVE-2025-24459 is a reflected Cross-Site Scripting (XSS) vulnerability affecting JetBrains TeamCity, a popular continuous integration and continuous deployment (CI/CD) server used by development teams worldwide. The vulnerability exists in the Vault Connection page, where user-supplied input is improperly handled and reflected back to users without adequate sanitization, enabling attackers to inject and execute arbitrary JavaScript code in the context of a victim's browser session.

Critical Impact

Attackers can exploit this XSS vulnerability to steal session cookies, hijack user accounts, perform actions on behalf of authenticated users, or redirect users to malicious websites. In CI/CD environments, this could lead to supply chain compromise or unauthorized access to build pipelines.

Affected Products

• JetBrains TeamCity versions prior to 2024.12.1

Discovery Timeline

• 2025-01-21 - CVE CVE-2025-24459 published to NVD
• 2025-01-30 - Last updated in NVD database

Technical Details for CVE-2025-24459

Vulnerability Analysis

This reflected XSS vulnerability (CWE-79) affects the Vault Connection page in JetBrains TeamCity. The vulnerability allows an attacker to craft a malicious URL containing JavaScript code that, when clicked by an authenticated user, executes within that user's browser session. The attack requires user interaction—specifically, a victim must click a maliciously crafted link.

The scope of the vulnerability extends beyond the vulnerable component itself, potentially affecting other resources and sessions within the same security context. An attacker can leverage this vulnerability to access sensitive information displayed in the TeamCity interface or perform unauthorized actions with the privileges of the authenticated victim.

Root Cause

The root cause of CVE-2025-24459 is insufficient input validation and output encoding on the Vault Connection page. When user-supplied data is processed and reflected back in the HTTP response, the application fails to properly sanitize or encode special characters that could be interpreted as HTML or JavaScript code. This allows malicious scripts embedded in request parameters to be executed in the victim's browser.

Attack Vector

The attack is network-based and requires an attacker to convince a victim to click on a specially crafted URL. The typical attack flow involves:

1. An attacker identifies the vulnerable parameter on the Vault Connection page
2. The attacker crafts a malicious URL containing JavaScript payload in the vulnerable parameter
3. The attacker delivers this URL to the victim through phishing emails, social engineering, or other means
4. When the victim (authenticated TeamCity user) clicks the link, the malicious script executes in their browser
5. The script can then steal session tokens, perform CSRF attacks, or exfiltrate sensitive data

The vulnerability does not require any privileges to exploit, though it does require user interaction. The impact includes potential compromise of session confidentiality and integrity, particularly dangerous in CI/CD environments where TeamCity may have access to source code repositories, build artifacts, and deployment credentials.

Detection Methods for CVE-2025-24459

Indicators of Compromise

• Review web server access logs for suspicious requests to the Vault Connection page containing encoded script tags or JavaScript event handlers
• Monitor for unusual URL parameters containing characters like <, >, script, javascript:, or URL-encoded variants
• Check for anomalous session activity following clicks on external links by TeamCity users

Detection Strategies

• Deploy Web Application Firewall (WAF) rules to detect and block common XSS payload patterns in requests to TeamCity
• Implement Content Security Policy (CSP) headers to restrict script execution sources and mitigate XSS impact
• Enable detailed logging for authentication events and monitor for session hijacking indicators
• Use browser-based endpoint protection that can detect and block reflected XSS attacks

Monitoring Recommendations

• Configure SIEM alerts for requests containing XSS-related patterns targeting TeamCity endpoints
• Monitor outbound connections from user browsers accessing TeamCity for data exfiltration attempts
• Track and alert on unusual administrative actions in TeamCity that may indicate compromised sessions
• Regularly audit access patterns to the Vault Connection page for anomalies

How to Mitigate CVE-2025-24459

Immediate Actions Required

• Upgrade JetBrains TeamCity to version 2024.12.1 or later immediately
• Review TeamCity access logs for any signs of exploitation attempts
• Educate users about the risks of clicking untrusted links, especially those pointing to internal systems
• Consider implementing additional network segmentation to limit exposure of TeamCity instances

Patch Information

JetBrains has addressed this vulnerability in TeamCity version 2024.12.1. Organizations should upgrade to this version or later as soon as possible. For detailed information about this and other security fixes, refer to the JetBrains Security Issues Fixed page.

Workarounds

• Restrict access to TeamCity to trusted networks only using firewall rules or VPN requirements
• Implement a reverse proxy with XSS filtering capabilities in front of TeamCity
• Deploy Content Security Policy headers to limit the impact of any successful XSS exploitation
• Consider disabling or restricting access to the Vault Connection functionality until the patch can be applied

# Example: Content Security Policy header configuration for Apache
# Add to TeamCity virtual host configuration
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'self';"