CVE-2021-31909 in TeamCity
Summary
by MITRE • 05/11/2021
In JetBrains TeamCity before 2020.2.3, argument 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-2021-31909 represents a critical security flaw in JetBrains TeamCity versions prior to 2020.2.3, where improper input validation allows for argument injection attacks that can escalate to remote code execution. This vulnerability stems from insufficient sanitization of user-supplied parameters within the application's command execution mechanisms, creating a pathway for malicious actors to inject arbitrary command arguments that are subsequently executed by the system.
The technical implementation of this vulnerability occurs within TeamCity's build agent and server components where user-provided data is directly incorporated into system commands without adequate validation or escaping. When administrators or users configure build steps, define parameters, or interact with the web interface, the application fails to properly sanitize inputs that are later used in shell commands or system calls. This design flaw aligns with CWE-77 and CWE-88 categories, which specifically address command injection vulnerabilities where attacker-controlled data is interpreted as command arguments.
The operational impact of this vulnerability is severe and multifaceted, as it allows remote attackers to execute arbitrary code on affected TeamCity servers with the privileges of the running service account. Attackers can leverage this vulnerability to gain full control over the build infrastructure, potentially leading to data breaches, system compromise, and disruption of continuous integration processes. The vulnerability affects organizations that rely on TeamCity for automated build and deployment workflows, making it particularly dangerous in enterprise environments where build servers often have elevated privileges and access to sensitive code repositories and production systems.
The exploitation of CVE-2021-31909 follows patterns consistent with ATT&CK technique T1059.001 for command and script injection, where adversaries manipulate application inputs to execute malicious commands. The vulnerability is particularly concerning because it requires no authentication for exploitation in many scenarios, making it accessible to attackers who can simply interact with the TeamCity web interface. Organizations using older versions of TeamCity should immediately implement mitigations including patching to version 2020.2.3 or later, implementing network segmentation to limit access to TeamCity servers, and conducting thorough security reviews of build configurations to identify potential injection points. Additionally, monitoring for unusual command executions and implementing proper input validation controls at multiple layers of the application architecture can help detect and prevent exploitation attempts.