CVE-2026-63077

CVE-2026-63077 is a critical (CVSS 9.8) unauthenticated remote code execution vulnerability in JetBrains TeamCity, caused by deserialization of untrusted data (CWE-502) in the agent polling protocol. An attacker with network access to the TeamCity server, but no credentials of any kind, can send maliciously crafted serialized input to the agent polling endpoint and execute arbitrary code on the server. Successful exploitation yields full server takeover, exposing source code, build logs, stored secrets and credentials, and providing a pivot point into build agents and connected infrastructure; related headlines describe a real breach in which AWS credentials were extracted from an unpatched TeamCity instance. Organizations running TeamCity On-Premises in versions prior to the fixes (2025.11.7 or 2026.1.3, depending on branch) are affected, while the JetBrains-hosted cloud service is not indicated as impacted. Exploitation is confirmed in the wild: CISA added the flaw to the Known Exploited Vulnerabilities catalog on 2026-08-05, EPSS is 86.5% (100th percentile), and no public PoC is known, meaning defenders cannot rely on public scanners alone and should assume sophisticated attackers are targeting exposed servers.

What to do: Upgrade immediately to TeamCity 2025.11.7 or 2026.1.3, whichever branch you run; because the flaw is pre-authentication, also hunt for signs of compromise (unexpected builds or agents, new or modified admin users, altered build configurations, and leaked stored credentials/secrets) per vendor guidance, and restrict internet exposure of the TeamCity server until patched. Federal agencies must apply vendor mitigations or discontinue use per CISA BOD 26-04 and the KEV required action, including the Forensics Triage Requirements.