PoC Releases for CVE-2026-63077: TeamCity RCE Exploited in the Wild

TL;DR

CVE-2026-63077 is a critical unauthenticated remote code execution flaw in JetBrains TeamCity. An attacker who reaches the server can run OS commands without credentials. CISA confirmed the vulnerability is exploited in the wild. Full technical details and proof-of-concept exploit code are now public. A patch is available.

Why This Matters

TeamCity servers sit at the heart of build pipelines. As a result, a compromise can spread into source code, secrets, and downstream software. The risk here is not theoretical. On August 5, 2026, CISA added CVE-2026-63077 to its Known Exploited Vulnerabilities catalog, confirming exploitation in the wild.

The public release raises the stakes further. Both the vulnerability details and proof-of-concept exploit code are now openly available. JetBrains reported no known active exploitation at disclosure. However, that status changed within weeks.

How the Attack Works

The bug is an unsafe deserialization flaw in the agent polling protocol. Agent endpoints under /app/agents/v1 remain unauthenticated. Therefore, an attacker needs only HTTP or HTTPS access to the server.

At the root, a vulnerable server builds a permissive XStream allowlist. It adds TeamCity protocol classes but fails to remove XStream’s default permissions. Consequently, broad type-hierarchy permissions expose enough callbacks to build a working gadget chain. The chain achieves remote code execution with the privileges of the TeamCity server process.

Exploitation Status

Rapid7 Labs published a full analysis and a proof-of-concept script. The exploit writes a malicious file to trigger command execution, then cleans up. This confirms a reliable path to remote code execution.

Affected Versions

The flaw affects JetBrains TeamCity version 2026.1.2 and earlier. Rapid7 compared this build against the fixed 2026.1.3 release.

Patch and Mitigation

JetBrains fixed the flaw in TeamCity 2026.1.3. The patch adds NoTypePermission.NONE before the allowlist, making it exclusive. Admins should update at once and review logs for suspicious agent requests.

Support Our Threat Intelligence

If you find our CVE report and cybersecurity news helpful, consider supporting our work.

Buy Me a Coffee PayPal

Crypto

USDT (TRC20):

TN8BdV8cp4T1Cd28gK9qTAnZknzzuwyUtm Copy

USDT (ERC20):

0x3725e1a7d3bc5765499fa6aaafe307fabcd75bce Copy

Written by

@DdoS · Security Researcher

Do Son

Do Son is the Founder and Editor of SecurityOnline.info. Working in cybersecurity since 2013, he reports on vulnerabilities, malware, and emerging threats, providing timely analysis to help organizations and individuals stay ahead of evolving risks.