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HIGH severity

CVE-2025-53506 — tomcat-coyote

HIGHFix: apache/tomcat@2aa6261

CVE-2025-53506 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in org.apache.tomcat:tomcat-coyote. A fix is available for org.apache.tomcat:tomcat-coyote — see the affected versions and patch details below.

Apache Tomcat: DoS via excessive h2 streams at connection start

Also known asBIT-tomcat-2025-53506GHSA-25xr-qj8w-c4vf
Published
Updated
Affected
8 pkgs
Patched
6 / 8
Exploits
None indexed
Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-53506.

EPSS Exploitation Probability

via FIRST.org ↗
2.1%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs82th percentile — riskier than 82% of all scored CVEsHighest risk
0.00%0.88%1.76%2.63%0.4%2.1%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

8 pkgs affected
☕org.apache.tomcat:tomcat-coyote☕org.apache.tomcat:tomcat-coyote☕org.apache.tomcat:tomcat-coyote☕org.apache.tomcat:tomcat-coyote☕org.apache.tomcat.embed:tomcat-embed-core☕org.apache.tomcat.embed:tomcat-embed-core☕org.apache.tomcat.embed:tomcat-embed-core☕org.apache.tomcat.embed:tomcat-embed-core

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

8 total 6 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.apache.tomcat:tomcat-coyote≥ 11.0.0-M1&&< 11.0.911.0.9org.apache.tomcat:tomcat-coyote:11.0.9
☕Mavenorg.apache.tomcat:tomcat-coyote≥ 10.1.0-M1&&< 10.1.4310.1.43org.apache.tomcat:tomcat-coyote:10.1.43
☕Mavenorg.apache.tomcat:tomcat-coyote≥ 9.0.0.M1&&< 9.0.1079.0.107org.apache.tomcat:tomcat-coyote:9.0.107
☕Mavenorg.apache.tomcat:tomcat-coyote≥ 8.5.0No fix
☕Mavenorg.apache.tomcat.embed:tomcat-embed-core≥ 8.5.0No fix
☕Mavenorg.apache.tomcat.embed:tomcat-embed-core≥ 9.0.0.M1&&< 9.0.1079.0.107org.apache.tomcat.embed:tomcat-embed-core:9.0.107

Affected Products

1 product · 3 configurations
Application
tomcatapache
≥ 11.0.0 && ≤ 11.0.8
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.tomcat:tomcat-coyote, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.apache.tomcat:tomcat-coyote to 11.0.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-53506 is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate
Workaround published by Red Hat
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Source: Red Hat security advisory for CVE-2025-53506 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat Enterprise Linux 10tomcat9-1:9.0.87-5.el10_0.3RHSA-2025:14178
Red Hat Enterprise Linux 10tomcat-1:10.1.36-1.el10_0.2RHSA-2025:14179
Red Hat Enterprise Linux 8tomcat-1:9.0.87-1.el8_10.6RHSA-2025:14177
Red Hat Enterprise Linux 8.8 Telecommunications Update Servicetomcat-1:9.0.87-1.el8_8.7RHSA-2025:14182
Red Hat Enterprise Linux 9tomcat-1:9.0.87-3.el9_6.3RHSA-2025:14181
Red Hat Enterprise Linux 9.2 Update Services for SAP Solutionstomcat-1:9.0.87-1.el9_2.6RHSA-2025:14183
Red Hat Enterprise Linux 9.4 Extended Update Supporttomcat-1:9.0.87-1.el9_4.6RHSA-2025:14180
Red Hat JBoss Web Server 5.8.5jws5-tomcatRHSA-2025:11696

Frequently Asked Questions

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.
O3 Security · Impact-Aware SCA

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CVE-2025-53506: tomcat-coyote — Fixed in 11.0.9