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Apache Tomcat CVE-2026-34486: CISA KEV Patch Checklist

August 6, 2026

Priority: CISA added CVE-2026-34486 to its Known Exploited Vulnerabilities catalog. Apache documents a narrowly scoped issue in the affected Tomcat clustering encryption component and provides fixed maintenance releases.

This guide applies to Apache Tomcat estates using the affected clustering encryption feature. It is intentionally focused on patch planning and verification, not technical reproduction.

Affected Apache Tomcat releases

  • Tomcat 9.0.116: update to 9.0.117 or later.
  • Tomcat 10.1.53: update to 10.1.54 or later.
  • Tomcat 11.0.20: update to 11.0.21 or later.

If the server does not use the relevant cluster-encryption component, record that conclusion as part of the exposure review. Do not assume a general Tomcat upgrade question answers the specific configuration question on its own.

Patch planning checklist

  1. Inventory Tomcat versions, application owners, cluster membership, and whether the affected encryption feature is enabled.
  2. Use the official Apache maintenance release for the running major line. Distribution-maintained packages should be updated through the supported operating-system channel when that is how Tomcat is installed.
  3. Drain traffic or schedule a maintenance window before touching clustered nodes. Keep enough healthy capacity available for the application’s documented availability plan.
  4. Upgrade one controlled node or a non-production equivalent first when the service design allows it, then verify application startup, session behavior, cluster health, and protected traffic settings.
  5. Complete the remaining nodes in the approved rolling order, then confirm that load balancing, monitoring, and alerting have returned to their normal state.
  6. Review the incident window for unexpected configuration changes or administrative access. Escalate with your incident process if anything cannot be explained.

Post-update validation

  • Confirm every production node is on its fixed release or a vendor-supported distribution package containing the fix.
  • Verify the application can serve its normal business-safe tests through the load balancer or reverse proxy.
  • Confirm cluster membership and encrypted cluster transport settings match the approved design.
  • Record the new version, maintenance window, validation result, and any deferred nodes in your change record.

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