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CVE-2026-65905 – Authentication Bypass via DIGEST Replay – Apache Tomcat 7.0.30–7.0.109, 8.5.0–8.5.1

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Summary

CVE-2026-65905 is an authentication bypass by capture-replay (CWE-294) affecting Apache Tomcat’s DIGEST authentication mechanism. The flaw allows a previously observed DIGEST-authenticated request to be replayed once under specific nonce-count conditions, and the CVE record assigns it a Critical CVSS v3.1 score of 9.8. It affects multiple actively supported and end-of-life Tomcat branches.

Technical details

  • Root cause: Tomcat’s DIGEST authenticator tracks a nonceCount and a replay window to prevent request replay; when a client makes a DIGEST-authenticated request with a nonceCount sitting on the upper boundary of the replay window before windowSize requests have been made, the replay-window check does not correctly reject a repeat of that request.
  • Trigger condition: A DIGEST-authenticated request whose nonceCount falls on the upper boundary of the configured replay window, while that nonceCount remains valid.
  • Attack vector: Network — an attacker who can capture or observe a qualifying DIGEST request can resubmit it once and have it accepted as authentic, without needing valid credentials or user interaction.
  • Impact: A captured request can be replayed successfully once, effectively bypassing the intended anti-replay protection of DIGEST authentication for that request.

Affected software

  • Apache Tomcat 11.0.0-M1 through 11.0.24
  • Apache Tomcat 10.1.0-M1 through 10.1.57
  • Apache Tomcat 9.0.0.M1 through 9.0.120
  • Apache Tomcat 8.5.0 through 8.5.100 (end of life)
  • Apache Tomcat 7.0.30 through 7.0.109 (end of life)

Severity

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

Mitigation and recommended actions

  • Immediate: Upgrade to Apache Tomcat 11.0.25, 10.1.58, or 9.0.121, which fix this issue.
  • If no patch is available: Tomcat 8.5.x and 7.0.x are end-of-life and do not have official fixed releases; organizations running these versions should migrate to a supported branch (9.0.121+, 10.1.58+, or 11.0.25+). Where DIGEST authentication is in use and patching cannot be performed immediately, consider disabling DIGEST authentication in favor of an alternative authentication scheme, or restricting network access to the affected service, until the upgrade can be completed.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Page title: Apache Tomcat followed by a version in parentheses, and Apache Tomcat/ followed by a version
  • Raw response body: a heading or paragraph containing Apache Tomcat/ followed by a version, and the text If you're seeing this, you've successfully installed Tomcat

References

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