Apache Tomcat EncryptInterceptor Padding Oracle Vulnerability (CVE-2026-29146) Security Advisory

1. Apply Official Security Patches

It is highly recommended to upgrade to the patched versions of Apache Tomcat:

• Tomcat 11.x users: Upgrade to 11.0.19 or later
• Tomcat 10.1.x users: Upgrade to 10.1.53 or later
• Tomcat 9.x users: Upgrade to 9.0.116 or later

2. Temporary Mitigation

If upgrading immediately is not feasible, modify your server.xml configuration to enforce an authenticated encryption algorithm (AEAD) such as AES/GCM/NoPadding instead of vulnerable CBC modes:

<!-- server.xml Configuration Example -->
<Interceptor className="org.apache.catalina.tribes.group.interceptors.EncryptInterceptor"
             encryptionAlgorithm="AES/GCM/NoPadding"
             encryptionKeyLength="16"
             providerName="SunJCE" />

Additionally, restrict access to the Tomcat clustering ports (typically 4000/TCP and UDP) using firewalls or security groups to ensure only trusted cluster nodes can communicate.

This vulnerability exists in the EncryptInterceptor component of Apache Tomcat, which is designed to secure communication between cluster nodes. Under default configurations, the interceptor is susceptible to a Padding Oracle attack due to improper handling of cryptographic padding validation errors (CWE-209, CWE-1240).

An attacker capable of intercepting cluster network traffic can send specially crafted ciphertexts and analyze the server's responses or timing differences. This allows the attacker to decrypt the ciphertext byte-by-byte, exposing highly sensitive cluster communication, including session replication data and administrative commands, leading to a complete loss of confidentiality.