CVE-2020-7910 in TeamCity
Summary
by MITRE
JetBrains TeamCity before 2019.2 was vulnerable to a stored XSS attack by a user with the developer role.
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Analysis
by VulDB Data Team • 01/31/2020
JetBrains TeamCity versions prior to 2019.2 contained a critical stored cross-site scripting vulnerability that allowed attackers with developer privileges to execute malicious scripts within the context of other users' browsers. This vulnerability falls under the CWE-79 category of Cross-Site Scripting and represents a significant security risk in continuous integration and deployment environments where multiple users collaborate on software development projects. The flaw enabled malicious input to be permanently stored within the TeamCity server and subsequently executed whenever affected users viewed the compromised content, creating a persistent threat vector that could affect all users with access to the vulnerable system.
The technical implementation of this vulnerability stemmed from insufficient input validation and output encoding mechanisms within TeamCity's web interface. Specifically, when developers created or modified build configurations, project settings, or other user-generated content, the application failed to properly sanitize user inputs before storing them in the database. This inadequate sanitization allowed malicious script payloads to be stored as part of legitimate user data, making the vulnerability particularly dangerous because it could persist across multiple user sessions and system restarts. The stored nature of the attack means that the malicious code would execute automatically whenever affected users accessed the compromised pages, without requiring additional user interaction beyond normal system usage.
The operational impact of this vulnerability extended beyond simple script execution, as it provided attackers with the ability to escalate privileges, steal session cookies, access sensitive project information, and potentially compromise the entire TeamCity infrastructure. Attackers could leverage this vulnerability to gain unauthorized access to build artifacts, source code repositories, and configuration data that would normally be restricted to authorized personnel. The attack surface was particularly concerning in enterprise environments where TeamCity serves as a central hub for software development workflows, as successful exploitation could lead to complete compromise of the CI/CD pipeline. Additionally, the vulnerability could be exploited to perform phishing attacks against other users, steal credentials, or redirect users to malicious websites that appear legitimate within the TeamCity interface.
Organizations should immediately update to TeamCity version 2019.2 or later to remediate this vulnerability, as JetBrains released this update specifically to address the stored XSS flaw. Security administrators should also implement additional monitoring and input validation measures to detect potential exploitation attempts, though the primary mitigation remains the software update. The vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as it enables attackers to execute scripts within user contexts, and T1566 for Phishing, since it could be used to craft convincing phishing attacks within the trusted TeamCity environment. Organizations should also review their user privilege models to ensure that only trusted individuals have developer roles, as this vulnerability requires at least developer-level access to exploit. The incident highlights the importance of proper input validation and output encoding practices, particularly in web applications that handle user-generated content, and underscores the need for regular security updates in development tooling environments.