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CVE-2026-76183 – Authentication Bypass – Apache Tomcat WebSocket Security Constraints

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Summary

CVE-2026-76183 is an Authentication Bypass by Alternate Name vulnerability (CWE-289) in Apache Tomcat that allows the security constraints protecting WebSocket endpoints to be bypassed entirely. The flaw stems from incorrect parsing of request paths as WebSocket endpoint templates, letting a remote, unauthenticated attacker reach protected WebSocket endpoints. The issue is rated Critical with a CVSS v3.1 base score of 9.8.

Technical details

  • Root cause: Tomcat incorrectly parses incoming request paths as WebSocket endpoint templates, causing security constraints defined for WebSocket endpoints to not be correctly applied/matched.
  • Trigger conditions: Any web application deployed on an affected Tomcat instance that exposes WebSocket endpoints protected by security constraints (e.g., authentication/authorization rules defined in web.xml or equivalent) is exposed.
  • Attack vector: Network-based, no authentication or user interaction required (AV:N/AC:L/PR:N/UI:N).
  • Impact: Successful exploitation bypasses access controls on WebSocket endpoints, allowing an attacker to reach functionality that should require authentication/authorization, with high impact to confidentiality, integrity, and availability.

Affected software

  • Apache Tomcat 11.0.0-M1 through 11.0.25
  • Apache Tomcat 10.1.0-M1 through 10.1.59
  • Apache Tomcat 9.0.0-M1 through 9.0.121
  • Apache Tomcat 8.5.0 through 8.5.100 (end of support, reported as affected)
  • Apache Tomcat 7.0.43 through 7.0.109 (end of support, reported as affected)

Severity

CVSS v3.1 Base Score: 9.8 (Critical)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade to a fixed release:
    • Apache Tomcat 11.0.26 or later
    • Apache Tomcat 10.1.60 or later
    • Apache Tomcat 9.0.122 or later
  • End-of-life versions (8.5.x, 7.0.x): These branches are no longer supported by the Apache Tomcat project and will not receive an official patch. Organizations still running these versions should migrate to a supported, patched branch (9.0.122+, 10.1.60+, or 11.0.26+) as soon as possible.
  • If immediate patching is not possible: Review and restrict network exposure of WebSocket endpoints, and audit whether any security-constraint-protected WebSocket endpoints are internet-facing until the upgrade can be applied.

References

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