Jetbrains TeamCity Agent Polling Protocol XML Deserialization Vulnerability Remote Code Execution Exploit

This module exploits CVE-2026-63077, a pre-authentication unsafe XML deserialization vulnerability in JetBrains TeamCity On-Premises. It registers a synthetic build agent through the agent polling protocol and submits a crafted XML document using the resulting agent session, without requiring TeamCity user credentials. Deserialization of the payload initializes an in-memory HSQLDB data source and uses HSQLDB's SCRIPT functionality to write a temporary JSP payload into the TeamCity ROOT web application. The module requests this JSP to execute an operating-system command as the account running the TeamCity server service. The JSP captures combined standard output and standard error, deletes itself when invoked, and is guarded against repeated execution. The module can verify the vulnerability, identify Linux or Windows targets, execute commands, and deploy an encrypted OSCI agent. It supports HTTP and HTTPS targets, including IPv6 addresses. Agent deployment is implemented for x86-64 Linux and Windows systems. Each command requires three HTTP requests: synthetic-agent registration, delivery of the deserialization payload, and invocation of the generated JSP. Commands are limited to 2026 characters, execution is limited to approximately 10 seconds, and captured output is limited to 1 MiB. Commands are executed with the privileges of the TeamCity server process. The exploit was tested against TeamCity 2025.11.6 on Ubuntu Linux 26.04 LTS and Windows Server 2025 Datacenter. Other vulnerable versions or platforms may also be affected but have not been verified by the engineering team.