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CVE-2026-86246 – Insecure Default TLS/OpenSSL Options Enabling MITM – Apache Tomcat Native 1.3.0–1.3

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Summary

CVE-2026-86246 is a vulnerability in Apache Tomcat Native — the native library that provides OpenSSL-based TLS support for Tomcat’s APR/native connector — in which several insecure OpenSSL options were enabled by default. The flaw is classified as CWE-1188 (Initialization of a Resource with an Insecure Default) and carries a CVSS v3.1 base score of 9.1 (Critical), reflecting network-exploitable weaknesses that can undermine the confidentiality and integrity of TLS connections handled by affected Tomcat deployments.

Technical details

  • Root cause: Tomcat Native shipped with the OpenSSL flags ALLOW_CLIENT_RENEGOTIATION, NO_EXTENDED_MASTER_SECRET, IGNORE_UNEXPECTED_EOF, and ALLOW_NO_DHE_KEX enabled by default, rather than requiring administrators to opt in to these weaker behaviors.
  • Trigger conditions: No special configuration is required by an attacker; any TLS connection to a server using the vulnerable Tomcat Native library inherits these insecure defaults.
  • Attack vector: Network (AV:N) — an attacker interacting with the TLS-terminating endpoint can leverage the weakened renegotiation, missing extended master secret binding, unexpected-EOF tolerance, and non-ephemeral Diffie-Hellman key exchange options to weaken the security guarantees of the TLS session.
  • Impact: High confidentiality and integrity impact with no availability impact (C:H/I:H/A:N), consistent with weakened TLS session protections that could facilitate interception or tampering with data in transit.

Affected software

  • Apache Tomcat Native 1.3.0 through 1.3.8
  • Apache Tomcat Native 2.0.0 through 2.0.15
  • Earlier, unsupported (EOL) versions of Apache Tomcat Native may also be affected

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: Upgrade Apache Tomcat Native to version 2.0.16 (for the 2.0.x line) or 1.3.9 (for the 1.3.x line), both of which disable the insecure OpenSSL defaults.
  • If immediate patching is not possible: Review and explicitly disable/override the affected OpenSSL options (ALLOW_CLIENT_RENEGOTIATION, NO_EXTENDED_MASTER_SECRET, IGNORE_UNEXPECTED_EOF, ALLOW_NO_DHE_KEX) in the Tomcat Native/APR connector configuration until the upgrade can be applied.
  • Confirm which connector (APR/native vs. NIO/NIO2) is in use, since only deployments relying on the Tomcat Native library and its bundled OpenSSL are affected.

References

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