CVE-2025-53506: Apache Tomcat: DoS via excessive h2 streams at connection start
CVE-2025-52434Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') vulnerability in Apache Tomcat when using the APR/Native connector. This was particularly noticeable with client initiated closes of HTTP/2 connections. This issue affects Apache Tomcat: from 9.0.0.M1 through 9.0.106. Users are recommended to upgrade to version 9.0.107, which fixes the issue. CVE-2025-53506Uncontrolled 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. Users are recommended to upgrade to version 11.0.9, 10.1.43 or 9.0.107, which fix the issue.
Other sources
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.
— NVD
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
maven/org.apache.tomcat:tomcat-coyoteto a version that resolves this vulnerability.Fixed in 9.0.107 - Upgrade
Upgrade
maven/org.apache.tomcat:tomcat-coyoteto a version that resolves this vulnerability.Fixed in 10.1.43 - Upgrade
Upgrade
maven/org.apache.tomcat:tomcat-coyoteto a version that resolves this vulnerability.Fixed in 11.0.9 - Upgrade
Upgrade
Apache Tomcatto a version that resolves this vulnerability.Fixed in 11.0.9 - Upgrade
Upgrade
Apache Tomcatto a version that resolves this vulnerability.Fixed in 10.1.43 - Upgrade
Upgrade
Apache Tomcatto a version that resolves this vulnerability.Fixed in 9.0.107
Event History
Frequently Asked Questions
What is the severity of CVE-2025-53506?
CVE-2025-53506 is classified as a medium severity vulnerability due to the potential for resource exhaustion.
How do I fix CVE-2025-53506?
To fix CVE-2025-53506, upgrade Apache Tomcat to a version beyond 11.0.8, 10.1.42, or 9.0.106.
What products are affected by CVE-2025-53506?
CVE-2025-53506 affects Apache Tomcat versions from 11.0.0-M1 to 11.0.8, 10.1.0-M1 to 10.1.42, and 9.0.0-M1 to 9.0.106.
What is the nature of the vulnerability described in CVE-2025-53506?
CVE-2025-53506 is an uncontrolled resource consumption vulnerability that can occur if an HTTP/2 client fails to acknowledge the initial settings frame.
Can CVE-2025-53506 lead to a denial of service?
Yes, CVE-2025-53506 can potentially lead to denial of service due to excessive resource consumption by the vulnerable instance.