CVE-2026-63077 — JetBrains TeamCity: Insecure Deserialization | CVSS 9.8 CRITICAL

CRITICAL

CVSS 9.8 CRITICAL  ·  EPSS 1%  ·  JetBrains TeamCity

Severity Overview

Summary

In JetBrains TeamCity before 2026.1.3, 2025.11.7 unauthenticated remote code execution was possible via the agent polling protocol

What the Attack Looks Like

How it works: The application deserializes untrusted data without validation. A crafted payload triggers arbitrary code execution during the deserialization process itself.

If successfully exploited: Full confidentiality and integrity impact means an attacker can both read and modify sensitive data — useful for credential harvesting, data theft, or manipulating application state. High availability impact means the vulnerability can also cause a denial of service, which may be used for disruption or as a diversion during a broader attack.

Analyst Takeaway

The attack is launched over the network (remotely exploitable without physical access) and no authentication is required. This vulnerability is already in CISA KEV, which means exploitation has been confirmed in the wild — treat this as active risk, not theoretical exposure. The CVSS score places this in critical territory, so internet-facing systems and high-value assets should be prioritized for immediate remediation or compensating controls. In parallel with patching, defenders should review external exposure, hunt for signs of exploitation, and validate whether compensating controls are in place for vulnerable assets.

Detection Guidance

• CWE-502 — Deserialization of Untrusted Data
  • Serialized data in requests: Search request bodies and cookies for known serialization format signatures: Java (AC ED 00 05 hex / rO0 base64), PHP (O: object notation), Python pickle (\x80\x02 or cos), .NET ViewState.
  • Process execution post-deserialization: Deserialization exploits frequently trigger process execution during the deserialization step itself. Hunt for unexpected child processes spawned by the application process — especially Java apps spawning bash or PowerShell.
  • Network callbacks (out-of-band detection): Many deserialization exploits use DNS or HTTP callbacks to confirm exploitation. Monitor for unexpected outbound DNS lookups or HTTP requests from the application server, particularly to services like Burp Collaborator or Interactsh infrastructure.

Recommended Actions

Immediate (0–24 Hours)

• Inventory: Identify all systems running JetBrains TeamCity. Include production, staging, dev, and cloud environments — untracked instances are the most likely to remain unpatched.
• Validate internet-facing exposure: Determine which of the affected systems are reachable from the public internet. Prioritize these for immediate remediation or compensating controls.
• Apply compensating controls now: For systems that cannot be patched immediately, implement temporary mitigations: restrict access via firewall rules or ACLs, add WAF rules if applicable, disable or isolate the vulnerable component if feasible without breaking critical operations.

Remediation

• Apply the vendor patch: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
• CISA directive deadline: 2026-08-08 — this is the mandatory deadline for US federal civilian agencies under BOD 22-01. All organizations should treat this date as a strong target regardless of federal mandate.
• Verify remediation: After patching, confirm the correct version is installed on all affected hosts. Run a vulnerability scan or use your asset management tooling to verify — do not rely solely on change tickets.

Detection Coverage

• Unauthenticated exploitation monitoring: Because this vulnerability requires no authentication, internet-facing scanning and exploitation attempts may begin within hours of public disclosure. Ensure alerting is in place before the end of the day.
• Threat intelligence feeds: Monitor your TI feeds and vendor advisory channels for published indicators of compromise (IOCs), proof-of-concept exploit releases, or active campaign reporting associated with this CVE — these should trigger an immediate hunt even if no internal alerts have fired.

Detection Playbooks

Vulnerability Details

Additional Notes

https://blog.jetbrains.com/teamcity/2026/07/cve-2026-63077/; https://www.jetbrains.com/privacy-security/issues-fixed/ ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2026-63077