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CVE-2026-34486: Apache Tomcat EncryptInterceptor Fail-Open Bypass

Technical analysis shows CVE-2026-34486 is a one-line fail-open regression in Tomcat Tribes enabling unauthenticated RCE via Java deserialization.

CVE-2026-34486 is a fail-open regression in Tomcat's Tribes EncryptInterceptor, introduced while fixing the CVE-2026-29146 padding-oracle flaw; Apache rated it Important and NVD scores it 7.5 High. Decryption failures are now forwarded to an unfiltered ObjectInputStream, and public PoC repositories demonstrate unauthenticated RCE on default port 4000 when clustering, the EncryptInterceptor, a reachable receiver and deserialization gadgets are all present. Affected releases 9.0.116, 10.1.53 and 11.0.20 are fixed in 9.0.117, 10.1.54 and 11.0.21; Tomcat 8.5 is unaffected.

Related CVEs

  • EncryptInterceptor Bypass Exposes Cluster Traffic in Apache Tomcat
    CVE-2026-34486 is a missing-encryption vulnerability in Apache Tomcat in which the EncryptInterceptor, the component that encrypts Tomcat cluster communication, can be bypassed in a fail-open manner; the flaw was introduced as a regression by the fix for CVE-2026-29146. It affects Tomcat 11.0.20, 10.1.53 and 9.0.116, and is triggered when cluster communication is expected to be encrypted: an attacker positioned on the network path between cluster nodes receives inter-node traffic in cleartext. By reading that unencrypted traffic, the attacker can obtain sensitive data such as session payloads, potentially enabling session theft and authentication bypass as indicated by related reporting. Only deployments running the affected point releases with the EncryptInterceptor in use are impacted, including Tomcat shipped in Red Hat JBoss Web Server and Red Hat Enterprise Linux channels. The flaw is being actively exploited: CISA added it to the Known Exploited Vulnerabilities catalog on 2026-08-04, EPSS places 30-day exploitation probability at 98.6%, though no public proof-of-concept is known and ransomware use is unconfirmed.
    · Apache Tomcat 11.0.20, 10.1.53, 9.0.116 (fixed in 11.0.21, 10.1.54, 9.0.117) · Red Hat JBoss Web Server (ships affected Tomcat) KEVlarge
  • Padding Oracle vulnerability in Apache Tomcat's EncryptInterceptor with default configuration.
    Padding Oracle vulnerability in Apache Tomcat's EncryptInterceptor with default configuration. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.18, from 10.0.0-M1 through 10.1.52, from 9.0.13 through 9..115, from 8.5.38 through 8.5.100, from 7.0.100 through 7.0.109. Users are recommended to upgrade to version 11.0.19, 10.1.53 and 9.0.116, which fixes the issue.
    · apache tomcat

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