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CVE-2026-63077 – Unauthenticated RCE via Agent Polling Protocol – JetBrains TeamCity before 2026….

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Summary

CVE-2026-63077 is a critical unauthenticated remote code execution vulnerability in JetBrains TeamCity On-Premises, stemming from insecure deserialization of untrusted data (CWE-502) in the agent polling protocol. It affects all TeamCity On-Premises versions prior to 2026.1.3 and 2025.11.7, and carries a CVSS v3.1 base score of 9.8 (Critical). An unauthenticated remote attacker can exploit this flaw to execute arbitrary code on the TeamCity server with no credentials or user interaction required.

Technical details

  • Root cause: Deserialization of untrusted data (CWE-502) in TeamCity’s agent polling protocol — the communication channel used by build agents to poll the TeamCity server for jobs and configuration updates.
  • Trigger conditions: An attacker sends a crafted, malicious payload to the agent polling endpoint exposed over the network; no authentication, session token, or valid username is required.
  • Attack vector: Fully remote, over the network (AV:N). Attack complexity is low (AC:L), no privileges required (PR:N), no user interaction required (UI:N).
  • Impact: Full compromise of confidentiality, integrity, and availability — successful exploitation results in arbitrary code execution on the underlying server, enabling access to source code, build secrets, environment variables, CI/CD pipelines, and lateral movement through connected infrastructure.

Affected software

  • JetBrains TeamCity On-Premises — all versions before 2026.1.3 (2026.x branch)
  • JetBrains TeamCity On-Premises — all versions before 2025.11.7 (2025.11.x branch)

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector String: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade to TeamCity 2026.1.3 (if on the 2026.x branch) or TeamCity 2025.11.7 (if on the 2025.11.x branch), which contain the vendor-provided fix.
  • If immediate patching is not feasible: Restrict network access to the TeamCity server — particularly the agent polling port — to only trusted internal build agent IP ranges. Prevent any untrusted external network access to the TeamCity instance until the patch is applied.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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