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HIGH severity

CVE-2025-9784 — undertow-core

HIGHFix: undertow-io/undertow#1778

CVE-2025-9784 is a high-severity (CVSS 7.5) CWE-770 vulnerability in io.undertow:undertow-core. A fix is available for io.undertow:undertow-core — see the affected versions and patch details below.

Undertow: undertow madeyoureset http/2 ddos vulnerability

Also known asGHSA-95h4-w6j8-2rp8
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 7, 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-2025-9784.

EPSS Exploitation Probability

via FIRST.org ↗
2.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs84th percentile — riskier than 84% of all scored CVEsHighest risk
1.05%1.64%2.23%2.83%1.6%2.3%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

2 pkgs affected
☕io.undertow:undertow-core☕io.undertow:undertow-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

A flaw was found in Undertow where malformed client requests can trigger server-side stream resets without triggering abuse counters. This issue, referred to as the "MadeYouReset" attack, allows malicious clients to induce excessive server workload by repeatedly causing server-side stream aborts. While not a protocol bug, this highlights a common implementation weakness that can be exploited to cause a denial of service (DoS).

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenio.undertow:undertow-coreall versions2.2.38.Finalio.undertow:undertow-core:2.2.38.Final
☕Mavenio.undertow:undertow-core≥ 2.3.0.Alpha1&&< 2.3.20.Final2.3.20.Finalio.undertow:undertow-core:2.3.20.Final

Affected Products

8 products · 10 configurations
Application
build of apache camel for spring bootredhat
all
OS
enterprise linuxredhat
2 versions
8.09.0
Application
fuseredhat
1 version
7.0.0
Application
jboss enterprise application platformredhat
2 versions
7.0.08.0.0
Application
jboss enterprise application platform expansion packredhat
all
Application
process automationredhat
1 version
7.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update io.undertow:undertow-core to 2.2.38.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-9784 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 HatImportant

This vulnerability is rated with an Important severity. It is simple to exploit because it does not require authentication and could result in a Denial of Service (DoS). While some DoS flaws are classified as Moderate, “MadeYouReset” is Important because of the limited barriers (no specialized tooling or advanced…

Workaround published by Red Hat
No mitigation is currently available that meets Red Hat Product Security’s standards for usability, deployment, applicability, or stability.
Source: Red Hat security advisory for CVE-2025-9784 (CC BY 4.0)
ProductFixed inAdvisory
Red Hat build of Apache Camel 4.14.2 for Spring Boot 3.5.8undertow-coreRHSA-2025:23143
Red Hat JBoss Enterprise Application Platform 7.1 EUS for RHEL 7eap7-undertow-0:1.4.18-21.SP19_redhat_00001.1.ep7.el7RHSA-2026:33372
Red Hat JBoss Enterprise Application Platform 7.3 EUS for RHEL 7eap7-undertow-0:2.0.41-8.SP9_redhat_00001.1.el7eapRHSA-2026:33371
Red Hat JBoss Enterprise Application Platform 7.4.24io.undertow/undertow-core:2.2.39.Final-redhat-00001RHSA-2026:4924
Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7eap7-undertow-0:2.2.39-1.Final_redhat_00001.1.el7eapRHSA-2026:4915
Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 8eap7-undertow-0:2.2.39-1.Final_redhat_00001.1.el8eapRHSA-2026:4916
Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 9eap7-undertow-0:2.2.39-1.Final_redhat_00001.1.el9eapRHSA-2026:4917
Red Hat JBoss Enterprise Application Platform 8.0undertow-coreRHSA-2026:3892

Frequently Asked Questions

A flaw was found in Undertow where malformed client requests can trigger server-side stream resets without triggering abuse counters. This issue, referred to as the "MadeYouReset" attack, allows malicious clients to induce excessive server workload by repeatedly causing server-side stream aborts. While not a protocol bug, this highlights a common implementation weakness that can be exploited to cause a denial of service (DoS).
O3 Security · Impact-Aware SCA

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CVE-2025-9784: undertow-core DoS — Fixed in 2.2.38.Final