JetBrains Patches Critical RCE Vulnerability CVE-2026-63077 in TeamCity

Critical RCE in TeamCity Agent Polling Protocol

JetBrains has issued emergency patches for a maximum-severity flaw in TeamCity On-Premises servers that allows unauthenticated attackers to execute arbitrary operating system commands over HTTP or HTTPS. Tracked as CVE-2026-63077 with a CVSS v3 score of 9.8, the vulnerability stems from an authentication bypass defect within the TeamCity agent polling protocol.

The security defect impacts all legacy and modern releases of JetBrains TeamCity On-Premises. JetBrains confirmed that its managed TeamCity Cloud environment has already been patched and mitigated, and noted that there is currently no evidence of active exploitation in the wild. However, given the central role CI/CD platforms play in enterprise environments, unpatched internet-facing servers present an immediate target for initial access and supply chain compromise.

Vulnerability Mechanics and Technical Context

In a standard TeamCity architecture, build agents continuously poll the central TeamCity server over HTTP/S to check for queued build jobs, report build statuses, upload logs, and retrieve configuration details. Because build agents operate across varied network topologies—including remote cloud instances, on-premises build farms, and isolated VLANs—the agent polling protocol endpoints must necessarily be reachable over standard web ports.

CVE-2026-63077 exists because the server fails to properly validate authentication checks on requests handled by the agent communication logic. By crafting malicious requests to these exposed agent polling endpoints, an unauthenticated remote attacker can bypass access controls entirely. Once past the authentication layer, the flaw permits the injection and execution of arbitrary OS commands with the full system privileges of the account running the TeamCity server process.

Authentication bypasses in CI/CD agent protocols are particularly dangerous because they convert endpoints meant for automated agent-server handshake routines into direct remote command execution channels. Attackers do not need valid user credentials, session tokens, or pre-existing access to any project workspace to achieve full execution.

The CI/CD Blast Radius: Supply Chain and Enterprise Exposure

Centralized continuous integration and continuous delivery (CI/CD) servers represent prime targets for sophisticated attackers. A compromise at the TeamCity server level delivers far-reaching impact across an organization’s entire technology stack:

1. Credential Harvesting: TeamCity servers store extensive vaults of sensitive secrets required for automated build and deployment pipelines. This includes cloud service provider API keys (AWS, Azure, GCP), private SSH keys, code signing certificates, database credentials, and personal access tokens (PATs) for version control platforms like GitHub and GitLab.
2. Build Artifact Tampering: Attackers with server-level access can manipulate active build pipelines, inject malicious code or backdoors into software binaries, and poison build artifacts before they reach production environments or end users.
3. Lateral Movement: Because TeamCity servers orchestrate workloads across build agents, compromising the central server allows an attacker to control connected build nodes across internal network segments, bypassing perimeter firewalls.
4. Source Code Exfiltration: Access to the TeamCity server allows complete visibility into proprietary source code repositories pulled down during automated build routines.

Because CI/CD servers sit at the intersection of development networks, source control management systems, and production deployment environments, an unauthenticated command execution flaw effectively hands attackers administrative dominion over the organization’s delivery pipelines.

Affected Versions and Remediation Path

The vulnerability affects all TeamCity On-Premises installations regardless of release version. JetBrains has provided two distinct remediation paths depending on an organization’s current deployment version:

• Upgrading to Fixed Versions: JetBrains has resolved CVE-2026-63077 in TeamCity On-Premises versions 2025.11.7 and 2026.1.3. Upgrading to these versions or higher completely remediates the underlying defect.
• Security Patch Plugin for Legacy Installations: For organizations running older versions that cannot immediately undergo a full platform upgrade, JetBrains has released a standalone security patch plugin compatible with TeamCity 2017.1 and newer. This plugin specifically addresses and remediates CVE-2026-63077 without requiring a full server upgrade.

JetBrains Cloud instances have already been updated on the backend, requiring no action from cloud customers.

Hardening Recommendations

To reduce exposure while applying updates, security teams should immediately enforce defensive controls around TeamCity installations:

• Restrict Network Exposure: Remove TeamCity server web interfaces and agent polling ports from the public internet. Access to the management interface and agent endpoints should be strictly gated behind a Virtual Private Network (VPN), zero-trust network access (ZTNA) solution, or restricted IP allowlists.
• Apply Least Privilege: Ensure the underlying operating system user running the TeamCity server process is granted only the minimum necessary system privileges. Never run the TeamCity service under high-privilege system accounts like Windows SYSTEM or Linux root.
• Architectural Segregation: Run TeamCity servers on dedicated host infrastructure separate from build agents. Isolate build agents in segmented networks so that a compromise of an agent or server does not automatically grant network-wide access.
• Audit Agent Communications: Inspect reverse proxy and web server logs for anomalous HTTP/S requests targeted at TeamCity agent polling endpoints, looking for unusual user-agents, command injection patterns, or unexpected source IP addresses.