CVE-2025-52879 is a reflected Cross-Site Scripting (XSS) vulnerability identified in JetBrains TeamCity, specifically affecting versions prior to 2025.03.3. The vulnerability arises in the NPM Registry integration component of TeamCity, a widely used continuous integration and continuous delivery (CI/CD) server. Reflected XSS (CWE-79) occurs when untrusted input is immediately returned by a web application without proper sanitization or encoding, allowing an attacker to inject malicious scripts into the victim’s browser. In this case, the flaw allows an attacker to craft a malicious URL or input that, when processed by the vulnerable TeamCity server, reflects the injected script back in the HTTP response. This can lead to the execution of arbitrary JavaScript in the context of the victim’s browser session. The CVSS 3.1 base score is 4.8 (medium severity), with the vector indicating network attack vector (AV:N), low attack complexity (AC:L), requiring high privileges (PR:H), user interaction (UI:R), scope changed (S:C), and low impact on confidentiality and integrity, with no impact on availability. The requirement for high privileges and user interaction reduces the ease of exploitation, but the scope change indicates that a successful exploit could affect components beyond the initially vulnerable scope, potentially impacting other parts of the system or user sessions. No known exploits are currently reported in the wild, and no official patches or mitigation links are provided yet. Given TeamCity’s role in automating build and deployment pipelines, exploitation could allow attackers to execute scripts that steal session tokens, perform actions on behalf of authenticated users, or manipulate CI/CD workflows, potentially leading to further compromise within development environments.

For European organizations, the impact of this vulnerability can be significant, especially for those relying heavily on JetBrains TeamCity for their software development lifecycle automation. The reflected XSS could enable attackers to hijack authenticated sessions of privileged users, such as developers or DevOps engineers, leading to unauthorized access to build configurations, source code repositories, or deployment pipelines. This could result in the injection of malicious code into software builds, supply chain compromise, or leakage of sensitive intellectual property. Given the interconnected nature of CI/CD environments, even a medium-severity vulnerability can cascade into more severe consequences if leveraged as part of a multi-stage attack. The requirement for high privileges limits exploitation to insiders or attackers who have already gained some level of access, but the user interaction requirement means phishing or social engineering could be used to trigger the attack. European organizations in sectors with stringent compliance requirements (e.g., finance, healthcare, critical infrastructure) may face regulatory and reputational risks if such a vulnerability is exploited. Additionally, the scope change in the CVSS vector suggests that the vulnerability could affect multiple components or user roles, increasing the potential attack surface within affected environments.

1. Immediate upgrade to JetBrains TeamCity version 2025.03.3 or later once available, as this version addresses the reflected XSS vulnerability in the NPM Registry integration. 2. Until patching is possible, restrict access to the TeamCity web interface to trusted networks and users, minimizing exposure to potential attackers. 3. Implement strict Content Security Policy (CSP) headers on the TeamCity server to limit the execution of unauthorized scripts and reduce the impact of XSS attacks. 4. Conduct user awareness training focused on phishing and social engineering risks, as user interaction is required for exploitation. 5. Review and harden user privileges within TeamCity, ensuring that only necessary users have high-level permissions to reduce the pool of potential attackers. 6. Monitor TeamCity logs and web traffic for unusual or suspicious requests that may indicate attempted exploitation of the reflected XSS vulnerability. 7. Employ web application firewalls (WAFs) with rules targeting reflected XSS patterns, specifically tuned for TeamCity’s NPM Registry integration endpoints. 8. Consider isolating CI/CD environments and enforcing network segmentation to limit lateral movement if an attacker exploits this vulnerability.