CVE-2026-63077 Overview
CVE-2026-63077 is an unauthenticated remote code execution vulnerability in JetBrains TeamCity affecting versions before 2026.1.3 and 2025.11.7. The flaw resides in the agent polling protocol and is classified under [CWE-502] Deserialization of Untrusted Data. An attacker with network access to the TeamCity server can execute arbitrary code without any credentials or user interaction. JetBrains addressed the issue in the fixed releases and documented it in the vendor's JetBrains Security Issues Fixed advisory.
Critical Impact
Unauthenticated attackers with network reach to the TeamCity server can achieve full remote code execution through the agent polling protocol, compromising the CI/CD pipeline and any downstream artifacts.
Affected Products
- JetBrains TeamCity versions before 2026.1.3
- JetBrains TeamCity versions before 2025.11.7
- TeamCity agent polling protocol endpoint
Discovery Timeline
- 2026-07-27 - CVE-2026-63077 published to NVD
- 2026-07-28 - Last updated in NVD database
Technical Details for CVE-2026-63077
Vulnerability Analysis
CVE-2026-63077 affects the TeamCity agent polling protocol, which build agents use to communicate with the central TeamCity server. The vulnerability is categorized under [CWE-502] Deserialization of Untrusted Data, indicating the server processes attacker-controlled serialized data without adequate validation. Successful exploitation yields code execution in the context of the TeamCity server process. Because TeamCity orchestrates build pipelines, code signing, and artifact publication, a compromise cascades into the software supply chain. The EPSS score at publication was 0.649% with a percentile of 47.49, reflecting early-stage exploitation prediction.
Root Cause
The root cause is unsafe deserialization within the agent polling protocol handler. The server accepts serialized objects from network callers and reconstructs them without enforcing type restrictions or authentication, allowing gadget chains to trigger arbitrary code paths. Because the protocol endpoint does not require authentication before deserialization occurs, any attacker able to reach the port participates in the exchange.
Attack Vector
Exploitation is network-based and requires no credentials, no user interaction, and low attack complexity. An attacker sends a crafted payload to the TeamCity agent polling endpoint. The server deserializes the payload, invoking gadget logic embedded in the object graph and executing attacker-supplied instructions. Because no verified public proof-of-concept code exists at the time of publication, refer to the JetBrains Security Issues Fixed advisory for authoritative technical details.
// No verified public exploit code is available for CVE-2026-63077.
// Refer to the JetBrains advisory for technical specifics on the
// agent polling protocol deserialization flaw.
Detection Methods for CVE-2026-63077
Indicators of Compromise
- Unexpected child processes spawned by the TeamCity server process, particularly shells, scripting interpreters, or download utilities.
- Outbound network connections from the TeamCity server to unfamiliar IP addresses following inbound traffic to the agent polling port.
- New or modified build configurations, plugins, or scheduled tasks that were not introduced by authorized administrators.
- Anomalous authentication artifacts or new service accounts appearing on the TeamCity host shortly after inbound polling traffic.
Detection Strategies
- Inspect TeamCity server logs for malformed or oversized agent polling requests and repeated deserialization exceptions.
- Correlate inbound connections to the agent polling port with process creation events on the TeamCity host to identify anomalous execution chains.
- Hunt for Java deserialization gadget patterns in HTTP request bodies destined for the TeamCity server.
Monitoring Recommendations
- Forward TeamCity server logs, host process telemetry, and network flow data to a centralized analytics platform for correlation.
- Alert on any process launched by the TeamCity service user that is not part of the documented build agent workflow.
- Monitor egress traffic from the TeamCity server to detect command-and-control callbacks or artifact exfiltration.
How to Mitigate CVE-2026-63077
Immediate Actions Required
- Upgrade TeamCity to version 2026.1.3 or 2025.11.7 or later without delay.
- Restrict network access to the TeamCity server so only trusted build agents and administrators can reach the agent polling port.
- Review recent build history, plugin installations, and administrative accounts for signs of tampering.
- Rotate credentials, tokens, and signing keys stored in or accessible to the TeamCity server if compromise is suspected.
Patch Information
JetBrains resolved CVE-2026-63077 in TeamCity 2026.1.3 and 2025.11.7. Consult the JetBrains Security Issues Fixed page for release notes and upgrade guidance. Apply the update to all self-hosted TeamCity servers; TeamCity Cloud tenants receive updates from the vendor.
Workarounds
- Place the TeamCity server behind a VPN or network segmentation boundary that blocks untrusted networks from reaching the agent polling port.
- Enforce strict firewall allowlists that permit connections only from known agent IP ranges until the patch is applied.
- Disable exposure of the TeamCity server to the public internet where the upgrade cannot be scheduled immediately.
# Example iptables rule restricting agent polling access to a trusted subnet
iptables -A INPUT -p tcp --dport 8111 -s 10.10.20.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8111 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
