JetBrains TeamCity Deserialization of Untrusted Data Vulnerability
TL;DR 📌
- In JetBrains TeamCity before 2026.1.3, 2025.11.7 unauthenticated remote code execution was possible via the agent polling protocol
- Highest CVSS: 9.8 (Critical).
- Listed in CISA KEV (2026-08-05) — this is being exploited in the wild.
- Fixed in
2025.11.7,2026.1.3— upgrade to this release or later. - CVEs: CVE-2026-63077.
What it is
CVE-2026-63077 is a deserialization of untrusted data vulnerability in JetBrains TeamCity, reachable through the agent polling protocol. TeamCity build agents poll the server for work, and this vulnerability sits in how the server handles data received over that channel.
The flaw allows unauthenticated remote code execution. There is no login or credential requirement — an attacker able to reach the agent polling endpoint over the network can trigger deserialization of attacker-controlled data, resulting in arbitrary code execution on the server. This is a network-vector, low-complexity attack (AV:N/AC:L/PR:N/UI:N), and the CVSS score of 9.8 reflects full compromise of confidentiality, integrity and availability.
Because TeamCity servers typically hold build pipeline configuration, source access, credentials for artifact repositories and deployment targets, remote code execution at this level exposes the whole CI/CD environment, not just the TeamCity instance itself.
This CVE is listed in the CISA Known Exploited Vulnerabilities catalogue, added on 2026-08-05, so it is known to be exploited.
What to do
- Patch immediately: fixed versions are TeamCity 2025.11.7 and 2026.1.3. Any deployment on an earlier build than the applicable fix line is exposed.
- If patching cannot happen immediately, restrict network access to the agent polling protocol endpoint so only known, trusted build agents can reach the TeamCity server — do not expose it to the general internet.
- Given the CISA KEV listing, treat this as a priority patch item under any KEV-driven remediation SLA your organisation follows, rather than routine patch cycles.
- After patching, review TeamCity server logs for any signs of unexpected agent connections or unusual process activity predating the update, and rotate credentials stored in or accessible from the TeamCity server (repository tokens, deployment keys, artifact repository credentials) if you cannot rule out prior compromise.
- Confirm the running version against 2025.11.7 or 2026.1.3 directly in the TeamCity administration UI rather than relying on package manager metadata alone.
For leadership 🧭
Executive summary. A critical, unauthenticated remote code execution flaw in JetBrains TeamCity is being actively exploited and gives full control of the build server, including its stored credentials for repositories and deployment targets. This needs emergency patching now, not at the next scheduled maintenance window.
Why it matters:
- The vulnerability is reachable via the agent polling protocol, the channel build agents use to fetch work from the TeamCity server, with no authentication needed to trigger it.
- Successful exploitation gives full compromise of confidentiality, integrity and availability (CVSS 9.8), meaning arbitrary code execution on the server itself.
- TeamCity servers typically hold credentials for artifact repositories, deployment targets and source access, so a compromise here can cascade into the wider CI/CD pipeline and downstream production systems.
- The CVE is listed in CISA’s Known Exploited Vulnerabilities catalogue, added 2026-08-05, confirming it is already being exploited in the wild.
Now / Next / Later:
- Now: Check the running TeamCity version in the administration UI and, if it is earlier than 2025.11.7 or 2026.1.3, restrict network access to the agent polling endpoint immediately so only trusted build agents can reach it.
- Next: Patch to TeamCity 2025.11.7 or 2026.1.3 in the next available change window, prioritised under KEV-driven remediation SLAs rather than routine patch scheduling.
- Later: After patching, review server logs for unexpected agent connections predating the fix and rotate repository, deployment and artifact credentials stored in or reachable from TeamCity if prior compromise cannot be ruled out.