CVE-2026-59084 Overview
CVE-2026-59084 affects Apache Tomcat due to insufficient technical documentation regarding the secure configuration of the EncryptInterceptor component. The EncryptInterceptor is used to secure cluster communications between Tomcat nodes. Because the requirements to configure it securely were not clearly documented, deployments relying on the default guidance may leave cluster traffic exposed to interception or manipulation. The vulnerability is tracked under CWE-1059 (Insufficient Technical Documentation) and impacts multiple long-supported Tomcat branches. Apache has published corrected guidance and fixed releases across the 9.x, 10.1.x, and 11.0.x lines.
Critical Impact
An attacker with network access to Tomcat cluster traffic can compromise the confidentiality and integrity of replicated session data when EncryptInterceptor is configured according to the previously incomplete documentation.
Affected Products
- Apache Tomcat 11.0.0-M1 through 11.0.23
- Apache Tomcat 10.1.0-M1 through 10.1.56
- Apache Tomcat 9.0.13 through 9.0.119
- Apache Tomcat 8.5.38 through 8.5.100 and 7.0.100 through 7.0.109 (end-of-support branches)
Discovery Timeline
- 2026-07-14 - CVE-2026-59084 published to NVD
- 2026-07-14 - Last updated in NVD database
Technical Details for CVE-2026-59084
Vulnerability Analysis
Apache Tomcat provides the EncryptInterceptor to encrypt communications between nodes in a cluster using symmetric cryptography. The interceptor sits in the cluster channel pipeline and is intended to protect session replication traffic from network attackers. The documentation shipped with affected releases did not fully describe the configuration parameters required to achieve authenticated encryption with proper key management. Administrators who followed the published guidance could deploy the interceptor in a state that did not deliver the intended cryptographic protections. Attackers on the cluster network segment could then read or modify replicated data in transit. The issue is classified as CWE-1059, reflecting that the security failure originates in documentation rather than a code defect.
Root Cause
The root cause is missing documentation of the secure configuration requirements for EncryptInterceptor. Operators had no authoritative reference describing the encryption modes, key lengths, or initialization behavior necessary to prevent replay, tampering, or downgrade of cluster messages. Deployments built against the incomplete documentation therefore inherit a weaker security posture than administrators intended.
Attack Vector
Exploitation requires network access to the Tomcat cluster communication channel. An adversary positioned on the internal network used for cluster replication can passively decrypt or actively manipulate messages exchanged between nodes. Successful exploitation impacts session state, replicated attributes, and any data conveyed through the cluster channel. Refer to the Apache Security Discussion and the OpenWall OSS-Security Update for the vendor-supplied technical narrative.
Detection Methods for CVE-2026-59084
Indicators of Compromise
- Unexpected session state changes or user impersonation events tied to clustered Tomcat nodes.
- Cluster replication traffic observed on network segments that were not expected to carry it.
- Log entries showing EncryptInterceptor initialization without the parameters required by the updated Apache guidance.
Detection Strategies
- Inventory all Tomcat installations and identify versions falling within the affected ranges for the 7.0.x, 8.5.x, 9.0.x, 10.1.x, and 11.0.x branches.
- Audit server.xml cluster configurations for EncryptInterceptor entries and compare them against the corrected Apache configuration requirements.
- Capture and inspect cluster channel traffic in a lab environment to confirm that authenticated encryption is active on production nodes.
Monitoring Recommendations
- Alert on Tomcat startup logs that instantiate EncryptInterceptor without the parameters mandated by the fixed versions.
- Monitor east-west network flows between Tomcat nodes for anomalous peers or unexpected traffic patterns.
- Track configuration drift on server.xml and cluster descriptor files using file integrity monitoring.
How to Mitigate CVE-2026-59084
Immediate Actions Required
- Upgrade Apache Tomcat to version 11.0.24, 10.1.57, or 9.0.120 as applicable.
- Retire deployments running end-of-support branches (7.0.x and 8.5.x) or migrate them to a supported release.
- Review every EncryptInterceptor configuration against the updated Apache documentation and rotate any keys that may have been exposed.
Patch Information
Apache has released fixed builds that ship with corrected documentation and configuration validation. Upgrade to Tomcat 11.0.24, 10.1.57, or 9.0.120. Details are provided in the Apache Security Discussion and the OpenWall OSS-Security Update.
Workarounds
- Restrict cluster communication to isolated, trusted network segments protected by strict segmentation and firewall rules.
- Terminate cluster traffic over an independently authenticated transport such as IPsec or a mutually authenticated VPN.
- Disable clustering on Tomcat instances that do not require session replication until patched versions are deployed.
# Configuration example
# Verify the running Tomcat version before and after patching
catalina.sh version
# Confirm EncryptInterceptor is present and review its parameters
grep -R "EncryptInterceptor" $CATALINA_BASE/conf/server.xml
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
