CVE-2021-31910 in TeamCity
Summary
by MITRE • 05/11/2021
In JetBrains TeamCity before 2020.2.3, information disclosure via SSRF was possible.
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Analysis
by VulDB Data Team • 05/15/2021
The vulnerability identified as CVE-2021-31910 represents a critical information disclosure flaw within JetBrains TeamCity versions prior to 2020.2.3. This issue stems from a server-side request forgery vulnerability that allows attackers to make unauthorized requests to internal systems that would otherwise be inaccessible from external networks. The vulnerability exists in the way TeamCity handles certain API requests and internal service communications, creating an attack surface where malicious actors can exploit the application's ability to fetch resources from arbitrary URLs. The flaw specifically affects the application's handling of remote resource access mechanisms that are intended for legitimate internal operations but can be manipulated by unauthorized users to access sensitive internal infrastructure components.
The technical implementation of this vulnerability involves the improper validation of user-supplied input in TeamCity's remote resource fetching functionality. When users submit requests that include URLs or resource identifiers, the application fails to adequately sanitize or restrict these inputs, allowing attackers to craft malicious requests that can traverse internal network boundaries. This particular flaw aligns with CWE-918, which describes server-side request forgery vulnerabilities where applications fail to properly validate and restrict external resource access. The vulnerability enables attackers to potentially access internal services, databases, or other sensitive resources that are typically protected by network segmentation and firewalls, effectively bypassing traditional perimeter security controls.
The operational impact of this vulnerability is significant for organizations relying on TeamCity for continuous integration and deployment operations. Attackers who successfully exploit this flaw can gain access to internal system information, potentially including credentials, configuration details, source code repositories, and other sensitive data stored within the internal network infrastructure. The vulnerability can be particularly dangerous in environments where TeamCity is integrated with internal authentication systems, version control repositories, or deployment targets that are not properly isolated from external access. Organizations may experience unauthorized data access, potential compromise of development environments, and exposure of intellectual property that could lead to substantial financial and operational losses.
Mitigation strategies for CVE-2021-31910 should prioritize immediate patching of TeamCity installations to version 2020.2.3 or later, which contains the necessary fixes for the SSRF vulnerability. Organizations should also implement network segmentation controls to limit direct access to TeamCity instances from untrusted networks, and establish strict firewall rules that prevent internal resource access from external requests. Additional defensive measures include implementing robust input validation for all user-supplied data, deploying web application firewalls to monitor and filter suspicious requests, and conducting regular security assessments of integrated systems to identify potential attack vectors. The mitigation approach aligns with ATT&CK technique T1071.004, which covers application layer protocol communication, and emphasizes the importance of validating and sanitizing all external inputs to prevent unauthorized resource access. Organizations should also consider implementing network monitoring solutions that can detect unusual patterns of internal resource access that might indicate exploitation attempts.