CVE-2021-31914 in TeamCity
Summary
by MITRE • 05/11/2021
In JetBrains TeamCity before 2020.2.4 on Windows, arbitrary code execution on TeamCity Server was possible.
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Analysis
by VulDB Data Team • 05/15/2021
The vulnerability identified as CVE-2021-31914 represents a critical arbitrary code execution flaw affecting JetBrains TeamCity server installations on Windows operating systems prior to version 2020.2.4. This vulnerability stems from insufficient input validation and improper privilege handling within the TeamCity server component that processes certain user-supplied data. The flaw allows an attacker to execute malicious code with the privileges of the TeamCity server process, which typically runs with elevated permissions on Windows systems. The vulnerability specifically impacts the Windows implementation of TeamCity and does not affect the Linux or macOS versions, highlighting the platform-specific nature of the security issue. Attackers could exploit this vulnerability through various means including but not limited to malicious project configurations, build scripts, or specially crafted user inputs that are processed by the TeamCity server.
The technical root cause of this vulnerability lies in the improper handling of file paths and execution contexts within TeamCity's build agent and server communication mechanisms. When TeamCity processes certain build configurations or project settings, it fails to adequately sanitize or validate the inputs before executing them in the Windows environment. This weakness creates an opportunity for attackers to inject malicious commands that get executed in the context of the TeamCity server process. The vulnerability is particularly dangerous because TeamCity servers often run with administrative privileges or at least elevated permissions, making successful exploitation directly translate into system compromise. The flaw falls under the category of command injection vulnerabilities and aligns with CWE-77 and CWE-94 as identified by the Common Weakness Enumeration catalog, which categorizes these issues as improper input validation leading to code execution.
The operational impact of CVE-2021-31914 extends far beyond simple system compromise, as TeamCity servers typically serve as central hubs for continuous integration and deployment processes within development organizations. Successful exploitation allows attackers to gain complete control over the build environment, potentially leading to code theft, build system manipulation, and further lateral movement within the network. Organizations relying on TeamCity for their CI/CD pipelines face significant risk as attackers could modify build scripts, inject malicious code into the build process, or even exfiltrate sensitive information from the development environment. The vulnerability's impact is amplified in environments where TeamCity servers have access to source code repositories, deployment targets, or other sensitive systems. According to ATT&CK framework, this vulnerability maps to techniques such as T1059.001 (Command and Scripting Interpreter: PowerShell) and T1068 (Exploitation for Privilege Escalation), demonstrating how attackers could leverage this weakness to achieve persistent access and escalate privileges within the target environment.
Organizations should immediately upgrade their TeamCity installations to version 2020.2.4 or later to remediate this vulnerability. The update includes proper input validation mechanisms and enhanced privilege handling that prevent the execution of malicious code through the identified attack vectors. System administrators should also implement network segmentation and access controls to limit exposure of TeamCity servers to untrusted networks. Additional mitigations include regular monitoring for unusual build activity, implementing strict build script validation procedures, and ensuring that TeamCity servers operate with the principle of least privilege. Security teams should conduct thorough vulnerability assessments to identify any systems running vulnerable versions and implement immediate patching procedures. The vulnerability also underscores the importance of maintaining up-to-date software versions and following secure coding practices to prevent similar issues in development environments. Organizations with critical infrastructure relying on TeamCity should consider implementing additional security controls such as build integrity verification and automated security scanning of build artifacts to prevent exploitation of similar vulnerabilities in the future.