CVE-2026-63077

Name of the Vulnerable Software and Affected Versions JetBrains TeamCity versions prior to 2026.1.3 JetBrains TeamCity versions prior to 2025.11.7

Description An unauthenticated remote code execution issue exists in the agent polling protocol due to insecure deserialization of XML data using the XStream library. An attacker can bypass authentication and execute arbitrary operating system commands with the privileges of the TeamCity server process by sending specially crafted HTTP requests to the endpoints /app/agents/v1/register and /app/agents/v1/commands/error. The exploitation involves using a gadget chain to write a malicious JSP file into the webroot, which is then executed via an HTTP request.

Real-world exploitation has been confirmed, including a significant breach of the JetBrains Cadence cloud service. In that incident, attackers accessed a full 2024 server backup, compromising personal user data, multiple AWS IAM credentials, and files in S3 buckets. There is also a possibility that source code synchronized from PyCharm projects was accessed. The breach resulted in the exposure of various secrets, including cloud credentials (AWS, Azure, GCP), source control tokens (GitHub, GitLab, Bitbucket), package registry credentials (npm, PyPI, Maven, NuGet), and container registry secrets.

Recommendations Update JetBrains TeamCity to version 2026.1.3 or later. Update JetBrains TeamCity to version 2025.11.7 or later. As a temporary mitigation, restrict access to the /app/agents/v1/* routes and limit HTTP/HTTPS port access to trusted IP addresses only. Install the JetBrains security patch plugin for versions 2017.1+ if an immediate upgrade is not possible. Run the TeamCity process under a limited OS account with minimal write permissions and restricted outbound network connections.