CVE-2026-55955: Apache Tomcat replay attack in EncryptionInterceptor cluster component

CVE-2026-55955 · Severity: medium · CVSS 6.5 · Published 2026-06-29

Apache Tomcat, a widely used web server and application container, contains a security flaw in its clustering component. This vulnerability allows an attacker to perform a 'replay attack,' where they intercept and resend valid encrypted messages to the server. This could potentially disrupt cluster operations or lead to unauthorized actions within the server environment.

Technologies: Apache Tomcat, org.apache.tomcat:tomcat (Maven), org.apache.tomcat:tomcat-tribes (Maven). Vendors: Apache, Maven.

Quick answers

Is CVE-2026-55955 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55955 being exploited in the wild.
How severe is CVE-2026-55955?
Medium severity, with a CVSS score of 6.5, published 29 June 2026.
Which products and versions are affected?
Apache Tomcat 11.0.0-M1 through 11.0.22, 10.1.0-M1 through 10.1.55, 9.0.13 through 9.0.18, 8.5.38 through 8.5.100, 7.0.100 through 7.0.109; org.apache.tomcat:tomcat (Maven) >= 11.0.0-M1, < 11.0.23, ECOSYSTEM:introduced=11.0.0-M1,fixed=11.0.23; org.apache.tomcat:tomcat-tribes (Maven) >= 11.0.0-M1, < 11.0.23, ECOSYSTEM:introduced=11.0.0-M1,fixed=11.0.23.
Is there a fix for CVE-2026-55955?
Yes. org.apache.tomcat:tomcat (Maven): upgrade to 11.0.23 or later; org.apache.tomcat:tomcat-tribes (Maven): upgrade to 11.0.23 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55955 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-55955?
Check whether you run Apache Tomcat, org.apache.tomcat:tomcat (Maven) or org.apache.tomcat:tomcat-tribes (Maven) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • org.apache.tomcat:tomcat (Maven): upgrade to 11.0.23 or later
    # set org.apache.tomcat:tomcat to 11.0.23 in your pom.xml or build.gradle
  • org.apache.tomcat:tomcat-tribes (Maven): upgrade to 11.0.23 or later
    # set org.apache.tomcat:tomcat-tribes to 11.0.23 in your pom.xml or build.gradle

Technical details

An improper authentication vulnerability exists in the Apache Tomcat clustering component's EncryptionInterceptor. The flaw allows for replay attacks because the interceptor does not sufficiently validate the uniqueness or freshness of encrypted messages received from other nodes in the cluster. An attacker with network access to the cluster communication channel could capture and re-inject encrypted packets to trigger unintended actions or state changes. The issue is resolved in versions 11.0.23, 10.1.56, and 9.0.119.

Affected products

  • Apache Tomcat 11.0.0-M1 through 11.0.22, 10.1.0-M1 through 10.1.55, 9.0.13 through 9.0.18, 8.5.38 through 8.5.100, 7.0.100 through 7.0.109

Identifiers

  • CVE-2026-55955
  • BIT-TOMCAT-2026-55955
  • GHSA-c5ph-rghf-fjfj

Timeline

  • 2026-06-29: disclosed
  • 2026-06-29: advisory

References

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