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
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
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-9784 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
io.undertow:undertow-core☕io.undertow:undertow-coreReal-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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.undertow:undertow-core | all versions | 2.2.38.Finalio.undertow:undertow-core:2.2.38.Final |
| ☕Maven | io.undertow:undertow-core | ≥ 2.3.0.Alpha1&&< 2.3.20.Final | 2.3.20.Finalio.undertow:undertow-core:2.3.20.Final |
Detection & mitigation playbook
Open-source dependencyDetect
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.
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.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-9784 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-9784. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
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.
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…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat build of Apache Camel 4.14.2 for Spring Boot 3.5.8 | undertow-core | RHSA-2025:23143 |
| Red Hat JBoss Enterprise Application Platform 7.1 EUS for RHEL 7 | eap7-undertow-0:1.4.18-21.SP19_redhat_00001.1.ep7.el7 | RHSA-2026:33372 |
| Red Hat JBoss Enterprise Application Platform 7.3 EUS for RHEL 7 | eap7-undertow-0:2.0.41-8.SP9_redhat_00001.1.el7eap | RHSA-2026:33371 |
| Red Hat JBoss Enterprise Application Platform 7.4.24 | io.undertow/undertow-core:2.2.39.Final-redhat-00001 | RHSA-2026:4924 |
| Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7 | eap7-undertow-0:2.2.39-1.Final_redhat_00001.1.el7eap | RHSA-2026:4915 |
| Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 8 | eap7-undertow-0:2.2.39-1.Final_redhat_00001.1.el8eap | RHSA-2026:4916 |
| Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 9 | eap7-undertow-0:2.2.39-1.Final_redhat_00001.1.el9eap | RHSA-2026:4917 |
| Red Hat JBoss Enterprise Application Platform 8.0 | undertow-core | RHSA-2026:3892 |
Frequently Asked Questions
Is CVE-2025-9784 in your dependencies?
O3 Security finds CVE-2025-9784 across Maven dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.