Fast Facts
- A critical vulnerability (CVE-2026-63077, CVSS 9.8) in on-premise TeamCity allows unauthenticated remote code execution, potentially enabling attackers to bypass authentication and run arbitrary OS commands.
- Exploitation via the agent polling protocol can lead to data exposure, configuration theft, or modification of server state, depending on server privileges.
- JetBrains recommends immediate updates or applying security patches to mitigate potential attacks, and advises enhancing network security for internet-facing TeamCity servers.
Threat, Attack Techniques, and Targets
JetBrains issued a warning about a serious security flaw called CVE-2026-63077 that affects all on-premise versions of TeamCity. This flaw is very dangerous and has a high severity score of 9.8 out of 10. Attackers can exploit this weakness to run any operating system commands on a TeamCity server without needing to log in.
The attacker would use the agent polling protocol to bypass security checks. This method allows remote code execution without authentication. If hackers succeed, they can control the server, access data, modify configurations, or steal stored credentials. The threat mainly targets organizations using on-premise TeamCity servers for their development and build processes.
Impact, Security Implications, and Guidance
The impact of this flaw is significant. Attackers can gain control of the server and do serious damage. Data exposure and server modification are possible consequences. Because of this, organizations face risks of data theft, disruption, or compromise of sensitive information.
JetBrains has fixed the issue in versions 2025.11.7 and 2026.1.3. and released a security patch plugin for older versions 2017.1+ for quick fixes. They recommend upgrading to the latest version for full security benefits.
Organizations should consider adding extra security layers, such as requiring VPN access or blocking internet-facing servers from outside access. Exposing login screens or APIs can help attackers find entry points to exploit vulnerabilities.
For detailed remediation steps, organizations should contact JetBrains or consult their official security guidance.
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