CVE-2026-100253 in TeamCity
Summary
by MITRE • 09/30/2026
In JetBrains TeamCity before 2026.2, 2026.1.4, 2025.11.8 sandbox escape leading to code execution was possible via the versioned settings Kotlin DSL
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified in JetBrains TeamCity prior to versions 2026.2, 2026.1.4, and 2025.11.8 represents a critical security flaw rooted in the improper isolation of the sandbox environment used for executing Kotlin DSL scripts within build configurations. This issue allows an attacker who has access to project-level settings or specific build configuration permissions to escape the restricted execution context imposed by the platform's security model. The core technical failure lies in how the versioned settings mechanism processes and evaluates dynamic code snippets, specifically those written in Kotlin Domain Specific Language (DSL). By crafting a maliciously constructed script that exploits parsing ambiguities or insufficient input validation within the DSL interpreter, an authenticated user can bypass the sandbox restrictions designed to prevent arbitrary command execution. This escape mechanism effectively grants the attacker the ability to execute operating system commands with the privileges of the TeamCity server process, which typically runs under high-privilege accounts such as root on Linux systems or SYSTEM on Windows servers.
From a technical perspective, this vulnerability is classified under CWE-94 Improper Control of Generation of Code (Code Injection) and specifically relates to CWE-250 Execution with Unnecessary Privileges. The flaw exploits the trust placed in the build configuration scripts by assuming that users with permission to edit these configurations are benign actors who will not attempt to escalate their privileges or compromise the underlying infrastructure. In reality, if an attacker gains access to a project where they can modify build steps involving Kotlin DSL, they can inject code snippets that interact directly with the host operating system's command interpreter. This interaction is facilitated by the fact that the sandbox environment does not adequately restrict low-level API calls or external process invocations when processing versioned settings updates. The use of Kotlin DSL introduces a layer of abstraction that may obscure the actual system calls being made, making it difficult for automated security scanners to detect such injections without deep semantic analysis of the script content.
The operational impact of this vulnerability is severe, as successful exploitation leads to full remote code execution on the TeamCity server host. An attacker can leverage this access to exfiltrate sensitive data stored within the CI/CD pipeline, including source code repositories credentials, deployment keys, and internal network configurations. Furthermore, because build servers often have privileged access to production environments or cloud infrastructure via integrated plugins and service accounts, compromising the TeamCity instance can serve as a pivot point for broader network compromise. Attackers may install persistent backdoors, modify build artifacts to inject malware into downstream deployments, or disrupt critical development workflows by corrupting project configurations. The ability to execute code with elevated privileges means that even if the application layer is secured against common web vulnerabilities like SQL injection or cross-site scripting, the underlying host remains vulnerable to complete takeover through this specific DSL execution path.
Mitigation strategies must prioritize immediate patching and access control hardening. JetBrains has addressed this issue in versions 2026.2, 2026.1.4, and 2025.11.8 by enhancing the sandbox isolation mechanisms and tightening validation rules for Kotlin DSL scripts within versioned settings. Organizations running affected versions should upgrade to one of these patched releases as soon as possible. In addition to patching, it is crucial to enforce strict least-privilege principles regarding who can edit build configurations that utilize Kotlin DSL. Administrators should review project permissions to ensure that only trusted users with a need-to-know basis have the ability to modify critical pipeline scripts. Implementing code review processes for all changes to build configuration files can also help detect malicious injections before they are executed. Furthermore, running TeamCity in an isolated environment with restricted network access and limited host privileges can reduce the blast radius of any potential exploitation attempt.
This vulnerability aligns with ATT&CK techniques related to Command and Scripting Interpreter abuse, specifically T1059 which covers various scripting languages used for execution. It also reflects patterns seen in CWE-78 Improper Neutralization of Special Elements used in an OS Command (OS Command Injection), although the vector is more nuanced due to its reliance on a domain-specific language parser rather than direct user input into shell commands. Security teams should monitor their environments for unusual process creation events originating from the TeamCity service account, particularly those involving common command-line interpreters or scripting engines that are not part of standard build operations. Regular audits of build configuration scripts and enabling detailed logging for DSL execution can provide early warning indicators of exploitation attempts. By combining timely software updates with robust access controls and continuous monitoring, organizations can effectively mitigate the risks associated with this sandbox escape vulnerability in JetBrains TeamCity.