A CI/CD server is rarely the first thing that comes to mind as exposed attack surface, but it holds the keys to everything: deploy credentials, private repository tokens, the key that signs an artifact before it ships to production. That's exactly the kind of system JetBrains patched on July 27, 2026, with a critical flaw in TeamCity On-Premises that allows remote code execution with no authentication at all.
The flaw: CVE-2026-63077
The National Vulnerability Database confirms a CVSS 3.1 score of 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), classified as CWE-502, deserialization of untrusted data. The vector is TeamCity's agent polling protocol: a remote attacker with no credentials at all, and only HTTP(S) access to the server, can bypass the authentication check and execute arbitrary operating system commands with the same privileges as the TeamCity server process. The flaw affects every On-Premises version prior to 2025.11.7, plus the 2026.1 line up to 2026.1.2. The fix ships in versions 2025.11.7 and 2026.1.3. TeamCity Cloud customers don't need to take action, the mitigation was already applied on the vendor side.
Why RCE on a build server outweighs a regular RCE
A CI/CD server concentrates exactly the kind of access any attacker wants: deploy credentials for production, private repository tokens, artifact signing keys, environment variables holding secrets for other connected systems. Compromising the TeamCity process isn't just running one isolated command, it's inheriting that entire access footprint. In practice, control over the build server opens the way to alter a pipeline, inject code into an artifact before it's published, or use the CI/CD system's own credentials to pivot into other systems. It's the same risk pattern behind the largest software supply chain incidents of recent years.
Confirmed exploitation in August
In the original advisory, JetBrains noted there was no evidence of active exploitation at the time of publication. That changed fast: on August 5, 2026, CISA added CVE-2026-63077 to its Known Exploited Vulnerabilities catalog, confirming exploitation against unpatched servers, with a remediation deadline of August 8 for US federal agencies. Two days later, on August 7, JetBrains published additional guidance reinforcing the urgency of patching for anyone who hadn't updated yet.
What to do now
- Upgrade to TeamCity 2025.11.7 or 2026.1.3, the fixed versions
- If a full upgrade isn't feasible right away, apply JetBrains' security patch plugin, available from version 2017.1 onward
- Restrict network access to the TeamCity server and the agent polling endpoint to trusted sources only, never exposed freely on the internet
- Rotate any credential, token, or secret stored in TeamCity if there's any indication the server was exposed before the patch
- Review recent build logs for altered pipelines or artifacts published outside the expected pattern
- Include the CI/CD server in the scope of your next pentest, with the same weight given to a production system
What this means for anyone evaluating a pentest engagement
CI/CD stopped being backstage infrastructure that only the platform team sees. It's attack surface with direct access to production, and an unauthenticated RCE on it is worth, in practice, as much as an RCE on a public-facing system. If a company's build server has never been in scope for a security test, that's the gap most worth closing first.