CVE-2025-53506 Apache Tomcat: DoS via excessive h2 streams at connection start

What is CVE-2025-53506?

CVE-2025-53506 is a high-severity denial of service vulnerability in Apache Tomcat, published on 10 Jul 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Uncontrolled Resource Consumption vulnerability in Apache Tomcat if an HTTP/2 client did not acknowledge the initial settings frame that reduces the maximum permitted concurrent streams.

This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.8, from 10.1.0-M1 through 10.1.42, from 9.0.0.M1 through 9.0.106. The following versions were EOL at the time the CVE was created but are known to be affected: 8.5.0 through 8.5.100. Other EOL versions may also be affected.

Users are recommended to upgrade to version 11.0.9, 10.1.43 or 9.0.107, which fix the issue.

Weakness: CWE-400

Which versions are affected by CVE-2025-53506?

17 open source packages ship an affected version, including org.apache.tomcat.embed:tomcat-embed-core, tomcat and org.apache.tomcat:tomcat-coyote. It affects 1 product.

Products include Apache Tomcat.

How do I fix CVE-2025-53506?

Upgrade org.apache.tomcat.embed:tomcat-embed-core to a fixed version for your release line: 10.1.43, 11.0.9 or 9.0.107.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2025-53506 being exploited?

There is no known exploitation of CVE-2025-53506 in the wild and no public exploit code.

Other vulnerabilities in Apache Tomcat

• CVE-2025-24813 Apache Tomcat Path Equivalence Exploited Critical 10.0
• CVE-2016-8735 Apache Tomcat Remote Code Execution Exploited Critical 9.8
• CVE-2017-12617 Apache Tomcat Remote Code Execution Exploited High 8.1
• CVE-2017-12615 Apache Tomcat on Windows Remote Code Execution Exploited High 8.1
• CVE-2026-34486 Apache Tomcat Missing Encryption of Sensitive Data Exploited High 7.5

All Apache Tomcat vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-tomcat-2025-53506, DEBIAN-CVE-2025-53506, GHSA-25xr-qj8w-c4vf, MINI-4h6v-p7v8-p24c, MINI-5x2j-9vh8-h88j, MINI-993j-xmpc-46fq and 5 more.