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CVE-2026-86248 – Authentication Bypass (CLIENT_CERT/OCSP) – Apache Tomcat 9.0.92–9.0.121, 10.1.22–10

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Summary

CVE-2026-86248 is an authentication bypass vulnerability (CWE-287: Improper Authentication) affecting Apache Tomcat. It stems from an incomplete fix for a prior issue, CVE-2026-34500, in which CLIENT_CERT authentication does not fail as expected in certain scenarios even when OCSP soft-fail checking is explicitly disabled. The issue is tracked with a CVSS v3.1 base score of 9.8 (Critical), reflecting the potential for authentication to succeed when it should be denied.

Technical details

  • Root cause: Tomcat’s certificate-based (CLIENT_CERT) authentication performs OCSP revocation checks against client certificates. A prior fix for CVE-2026-34500 addressed cases where OCSP checks would "soft-fail" (silently allow authentication) under the Foreign Function & Memory (FFM) API path even when administrators had disabled soft-fail. That fix was incomplete — additional scenarios still allow authentication to proceed without a valid OCSP result.
  • Trigger conditions: Deployments that use TLS client certificate authentication (CLIENT_CERT) with OCSP revocation checking configured and soft-fail explicitly disabled are affected. The flaw manifests when the OCSP check does not produce a definitive result but authentication is still permitted.
  • Attack vector: Network (remote, no authentication or user interaction required to attempt exploitation) — an attacker presenting an invalid, revoked, or otherwise non-validating client certificate may still be authenticated.
  • Impact: Successful exploitation undermines the integrity of certificate-based authentication, potentially allowing an attacker to bypass CLIENT_CERT authentication controls and gain unauthorized access to protected resources, resulting in loss of confidentiality, integrity, and availability of the affected application.

Affected software

  • Apache Tomcat 11.0.0-M14 through 11.0.25
  • Apache Tomcat 10.1.22 through 10.1.59
  • Apache Tomcat 9.0.92 through 9.0.121

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 Apache Tomcat release:
    • Tomcat 11.x → upgrade to 11.0.26
    • Tomcat 10.1.x → upgrade to 10.1.60
    • Tomcat 9.0.x → upgrade to 9.0.122
  • If unable to patch immediately: Review and restrict reliance on CLIENT_CERT authentication with OCSP revocation checking until upgraded; ensure OCSP responder availability and monitor authentication logs for anomalous client-certificate authentication events. Removing the bundled Tomcat examples web application is also recommended as general hardening, though it does not address the underlying authentication logic flaw.

References

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