CVE-2021-31915 in TeamCity
Summary
by MITRE • 05/11/2021
In JetBrains TeamCity before 2020.2.4, OS command injection leading to remote code execution was possible.
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Analysis
by VulDB Data Team • 05/15/2021
The vulnerability identified as CVE-2021-31915 represents a critical security flaw in JetBrains TeamCity versions prior to 2020.2.4 that enables unauthorized remote code execution through operating system command injection. This vulnerability exists within the build agent functionality of TeamCity, where user-supplied input is improperly sanitized before being passed to system commands. The flaw allows attackers to inject malicious operating system commands that are then executed with the privileges of the TeamCity build agent process, potentially compromising the entire continuous integration and deployment infrastructure.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization within TeamCity's build agent component. When users configure build steps or provide parameters to build agents, the system fails to properly escape or filter special characters that could be interpreted as command delimiters or operators. This creates an environment where an attacker can manipulate build configurations to execute arbitrary commands on the underlying operating system. The vulnerability is classified under CWE-78 as "Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')", which is a well-documented weakness in software security that has been exploited in numerous other systems throughout the industry.
The operational impact of CVE-2021-31915 extends beyond simple remote code execution, as it can lead to complete system compromise and data exfiltration. Attackers can leverage this vulnerability to escalate privileges, establish persistent backdoors, or access sensitive build artifacts and source code repositories. The attack surface is particularly concerning in continuous integration environments where build agents often run with elevated privileges to perform deployment tasks. According to ATT&CK framework domain ATT&CK-1059, this vulnerability maps directly to the "Command and Scripting Interpreter" technique, where adversaries use legitimate system tools to execute malicious commands. The exploitation of this vulnerability can result in unauthorized access to production environments, supply chain compromises, and significant business disruption.
Mitigation strategies for CVE-2021-31915 primarily focus on upgrading to TeamCity version 2020.2.4 or later, which includes proper input sanitization and command execution controls. Organizations should also implement network segmentation to limit access to TeamCity servers, enforce strict access controls, and monitor build agent activities for suspicious command execution patterns. Additional protective measures include disabling unnecessary build agent features, implementing web application firewalls, and conducting regular security audits of build configurations. The vulnerability highlights the importance of input validation in CI/CD environments where system commands are frequently executed, and organizations should follow security best practices outlined in NIST SP 800-53 for secure software development lifecycle practices.