CVE-2026-65637

Apache Tomcat - HTTP/2 no-authority bypass of strict SNI validation

Improper Input Validation vulnerability in Apache Tomcat due to incomplete fix for CVE-2026-32990.

This issue affects Apache Tomcat: from 11.0.20 through 11.0.24, from 10.1.53 through 10.1.57, from 9.0.115 through 9.0.120.

Users are recommended to upgrade to version 11.0.25, 10.1.59 or 9.0.121, which fix the issue.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2026-65637 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (11.0.25, 10.1.59, 9.0.121); upgrading removes the vulnerable code path.

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1. What is CVE-2026-65637? CVE-2026-65637 is a critical-severity improper input validation vulnerability in org.apache.tomcat:tomcat-coyote (maven), affecting versions >= 11.0.20, < 11.0.25. It is fixed in 11.0.25, 10.1.59, 9.0.121. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2026-65637? CVE-2026-65637 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-65637?
   • org.apache.tomcat:tomcat-coyote (maven) (versions >= 11.0.20, < 11.0.25)
   • org.apache.tomcat.embed:tomcat-embed-core (maven) (versions >= 11.0.20, < 11.0.25)
4. Is there a fix for CVE-2026-65637? Yes. CVE-2026-65637 is fixed in 11.0.25, 10.1.59, 9.0.121. Upgrade to this version or later.
5. Is CVE-2026-65637 exploitable, and should I be worried? Whether CVE-2026-65637 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-65637 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-65637?
   • Upgrade org.apache.tomcat:tomcat-coyote to 11.0.25 or later
   • Upgrade org.apache.tomcat:tomcat-coyote to 10.1.59 or later
   • Upgrade org.apache.tomcat:tomcat-coyote to 9.0.121 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 11.0.25 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 10.1.59 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 9.0.121 or later

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