CVE-2026-111094 in TeamCity
Summary
by MITRE • 10/15/2026
In JetBrains TeamCity before 2026.2, 2026.1.4, 2025.11.8 remote code execution via a whitelist bypass in the build messages protocol was possible
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in JetBrains TeamCity versions prior to 2026.2, specifically affecting builds running on version 2026.1.4 and patch level 2025.11.8, represents a critical remote code execution flaw rooted in the implementation of the build messages protocol. This security defect arises from an insufficient validation mechanism within the whitelist that governs how external inputs are processed during the build lifecycle. The build messages protocol is designed to facilitate communication between various components of the continuous integration and deployment pipeline, allowing for the transmission of status updates, logs, and configuration changes. However, the specific implementation in these affected versions failed to strictly enforce boundary conditions on certain input parameters, creating a pathway for attackers to bypass established security controls through carefully crafted payloads that exploit logical gaps in the filtering logic.
From a technical perspective, this vulnerability is classified under CWE-20 Improper Input Validation and aligns with ATT&CK technique T1059 Command and Scripting Interpreter, as it allows an adversary to execute arbitrary commands within the context of the TeamCity server process. The core issue lies in the parsing engine that interprets messages sent via the protocol. While a whitelist approach is generally considered a robust security practice by restricting operations to only those explicitly permitted, the implementation here suffered from a bypass flaw where specific sequences or encoded characters were not adequately sanitized before being passed to underlying system commands or internal execution handlers. This oversight enables an authenticated user with access to trigger build processes to inject malicious code that escapes the intended sandboxed environment of the build agent and executes on the server itself.
The operational impact of this vulnerability is severe, as successful exploitation grants attackers full remote code execution capabilities on the TeamCity server. This level of access allows for comprehensive compromise of the continuous integration infrastructure, including the ability to steal sensitive source code repositories, exfiltrate credentials stored in build configurations, and pivot further into internal network segments connected to or trusted by the CI/CD environment. Attackers can manipulate build artifacts, inject malware into deployed software, or establish persistent backdoors within the development pipeline. Given that TeamCity is often central to an organization's software delivery lifecycle, compromising this system undermines the integrity of all downstream applications and services built through it, potentially leading to widespread supply chain contamination if malicious code is propagated to production environments without detection.
Mitigation strategies must prioritize immediate patching to version 2026.2 or later, which addresses the whitelist bypass by hardening input validation routines within the build messages protocol handler. In scenarios where upgrading is not immediately feasible, organizations should implement strict network segmentation to isolate TeamCity servers from untrusted networks and restrict access to only authorized IP ranges using firewall rules. Additionally, enabling multi-factor authentication for all user accounts reduces the risk of unauthorized access that could lead to exploitation of this vulnerability. Security teams should also audit build configurations for any custom scripts or plugins that might interact with the messages protocol in unexpected ways, ensuring that no legacy components retain exploitable interfaces. Continuous monitoring of system logs for anomalous command execution patterns can aid in early detection and response efforts while remediation steps are being executed.