EncryptInterceptor Bypass Exposes Cluster Traffic in Apache Tomcat
CISA: Apache Tomcat Missing Encryption of Sensitive Data Vulnerability
CVSS 3.1
7.5high
EPSS
99%p100
Published
()
KEV added
AI analysis
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.
What to do: Upgrade Apache Tomcat to 11.0.21, 10.1.54 or 9.0.117, and apply the corresponding Red Hat JBoss Web Server / Enterprise Linux updates when published. Audit Tomcat cluster configurations for EncryptInterceptor usage, and until patched restrict or encrypt the network segment carrying inter-node cluster traffic. Because the flaw is in CISA's KEV catalog, federal agencies must patch per BOD 26-04 timelines and should review cluster nodes for signs of session data interception.
Affected
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)
—
Red Hat Enterprise Linux (including ELS, EUS, TUS, and Update Services for SAP Solutions)
—
Estimated exposure
largetens of thousands of Tomcat deployments on the affected point releases — Tomcat is one of the most widely deployed Java application servers, with hundreds of thousands of instances visible in public internet-exposure scans, but only the three specific point releases are vulnerable and the flaw is only…
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
Description
Missing Encryption of Sensitive Data vulnerability in Apache Tomcat due to the fix for CVE-2026-29146 allowing the bypass of the EncryptInterceptor. This issue affects Apache Tomcat: 11.0.20, 10.1.53, 9.0.116. Users are recommended to upgrade to version 11.0.21, 10.1.54 or 9.0.117, which fix the issue.
CISA Known Exploited Vulnerability
Affected
Apache Tomcat
Required action
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
tomcat, jboss web server, enterprise linux, enterprise linux els, enterprise linux eus, enterprise linux tus, enterprise linux update services for sap solutions
CISA added CVE-2026-34486, an actively exploited Apache Tomcat EncryptInterceptor bypass enabling unauthenticated deserialization RCE, to its KEV catalog.
CVE-2026-34486 allows bypass of Apache Tomcat's EncryptInterceptor, a flaw introduced by the fix for padding-oracle issue CVE-2026-29146 in Tribes cluster encryption. CISA added the flaw to the Known Exploited Vulnerability catalog on August 4, 2026, alongside actively exploited Langflow and N-central flaws, with remediation required under BOD 26-04 guidance. Official patches and workarounds are available, and reporting notes unauthenticated remote code execution through Java deserialization on the Tribes receiver port 4000.
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.
SentinelOne details CVE-2026-34486, an Apache Tomcat EncryptInterceptor bypass exposing unencrypted cluster communications, with patches and workarounds available.
CVE-2026-34486 stems from an incomplete fix for CVE-2026-29146, letting network-positioned attackers bypass the EncryptInterceptor and read plaintext Tomcat cluster traffic, including session and application data between nodes. Affected versions 9.0.116, 10.1.53 and 11.0.20 are fixed in 9.0.117, 10.1.54 and 11.0.21. Workarounds include network-level encryption such as IPsec or VPN tunnels and isolating cluster communications to secured network segments.