CVE-2026-86246 Overview
CVE-2026-86246 is an insecure default configuration vulnerability in Apache Tomcat Native. The library enables several unsafe Transport Layer Security (TLS) options by default, including ALLOW_CLIENT_RENEGOTIATION, NO_EXTENDED_MASTER_SECRET, IGNORE_UNEXPECTED_EOF, and ALLOW_NO_DHE_KEX. These options weaken TLS session security and expose deployments to downgrade, renegotiation abuse, and truncation attacks. The flaw is categorized under [CWE-1188] (Initialization of a Resource With an Insecure Default). It affects Apache Tomcat Native versions 2.0.0 through 2.0.15 and 1.3.0 through 1.3.8. Earlier unsupported branches may also be affected. Fixed releases are 2.0.16 and 1.3.9.
Critical Impact
Insecure TLS defaults expose Tomcat Native deployments to client-initiated renegotiation abuse, missing extended master secret protection, truncation attacks via unexpected end-of-file handling, and non-ephemeral key exchange, weakening confidentiality and integrity of TLS sessions.
Affected Products
- Apache Tomcat Native 2.0.0 through 2.0.15
- Apache Tomcat Native 1.3.0 through 1.3.8
- Earlier unsupported Apache Tomcat Native branches
Discovery Timeline
- 2026-09-23 - CVE-2026-86246 published to the National Vulnerability Database (NVD)
- 2026-09-23 - Last updated in NVD database
Technical Details for CVE-2026-86246
Vulnerability Analysis
Apache Tomcat Native provides Java Native Interface (JNI) bindings to OpenSSL for TLS termination in Apache Tomcat. The affected versions initialize the OpenSSL context with four options that OpenSSL treats as opt-in weakening flags. ALLOW_CLIENT_RENEGOTIATION permits clients to trigger TLS renegotiation, a well-known denial-of-service and session confusion vector. NO_EXTENDED_MASTER_SECRET disables the RFC 7627 extension that binds session keys to the full handshake, reintroducing exposure to triple-handshake attacks. IGNORE_UNEXPECTED_EOF suppresses errors when a peer closes a connection without a proper TLS close_notify, masking truncation attacks. ALLOW_NO_DHE_KEX allows TLS 1.3 handshakes without ephemeral Diffie-Hellman, removing forward secrecy for resumed sessions.
Root Cause
The root cause is unsafe defaults during context initialization. Administrators reasonably assume Tomcat Native configures OpenSSL with secure defaults, but the library explicitly enabled options that reduce TLS assurances. Deployments inherited these settings without any indication in configuration files.
Attack Vector
Exploitation occurs over the network against any TLS listener backed by Tomcat Native. An attacker positioned as a client or on-path adversary can trigger repeated renegotiation to exhaust server resources, downgrade session properties by leveraging the missing extended master secret, or truncate responses without detection. No authentication or user interaction is required.
No verified public exploit code is available for CVE-2026-86246. See the Apache Mailing List Thread and the Openwall OSS Security Post for the official disclosure.
Detection Methods for CVE-2026-86246
Indicators of Compromise
- Repeated TLS renegotiation requests from a single client IP against Tomcat listeners bound to the Native connector.
- TLS session logs showing handshakes completing without the extended_master_secret extension.
- Abrupt TCP FIN or RST closures without a preceding TLS close_notify recorded by network sensors.
- TLS 1.3 sessions negotiating without an ephemeral key share.
Detection Strategies
- Inventory Apache Tomcat installations and identify servers using the APR/Native connector by inspecting server.xml for protocol="org.apache.coyote.http11.Http11AprProtocol".
- Query installed tcnative-1 or tcnative-2 shared libraries and compare versions against 2.0.16 and 1.3.9.
- Use TLS scanners such as testssl.sh or sslyze to flag endpoints that accept client renegotiation or negotiate sessions without extended master secret.
Monitoring Recommendations
- Alert on high rates of TLS renegotiation events per source IP at the load balancer or web application firewall.
- Capture and review handshake metadata in centralized logs to confirm forward secrecy and extended master secret usage.
- Track Tomcat Native library versions across the estate as part of software bill of materials (SBOM) monitoring.
How to Mitigate CVE-2026-86246
Immediate Actions Required
- Upgrade Apache Tomcat Native to version 2.0.16 or 1.3.9, which set secure defaults for the four affected options.
- Restart all Tomcat instances after replacing the tcnative shared library to load the corrected defaults.
- Audit server.xml and any SSLHostConfig blocks to confirm no configuration explicitly re-enables the unsafe options.
Patch Information
The Apache Tomcat project fixed CVE-2026-86246 in Apache Tomcat Native 2.0.16 and 1.3.9. The fix disables ALLOW_CLIENT_RENEGOTIATION, NO_EXTENDED_MASTER_SECRET, IGNORE_UNEXPECTED_EOF, and ALLOW_NO_DHE_KEX by default. Refer to the Apache Mailing List Thread for the official advisory.
Workarounds
- Front Tomcat with a hardened reverse proxy such as nginx or httpd that terminates TLS with secure defaults.
- Disable the APR/Native connector and use the JSSE connector until the Tomcat Native library can be upgraded.
- Restrict inbound access to Tomcat listeners to trusted networks while the upgrade is scheduled.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
