CVE-2025-9784 Undertow: undertow madeyoureset http/2 ddos vulnerability
Malicious clients can cause denial of service in Undertow by triggering excessive server-side stream resets without hitting abuse counters.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-9784?
CVE-2025-9784 is a high-severity denial of service vulnerability in Redhat Enterprise Linux, published on 2 Sep 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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).
Which versions are affected by CVE-2025-9784?
4 open source packages ship an affected version, including io.undertow:undertow-core. It affects 8 products.
| Package | Affected | Fixed in |
|---|---|---|
io.undertow:undertow-core Maven | All versions | 2.2.38.Final |
io.undertow:undertow-core Maven | All versions | 2.2.38.Final |
io.undertow:undertow-core Maven | From 2.3.0.Alpha1 | 2.3.20.Final |
io.undertow:undertow-core Maven | From 2.3.0.Alpha1 | 2.3.20.Final |
Products include Redhat Build of Apache Camel for Spring Boot, Redhat Enterprise Linux, Redhat Fuse, Redhat Jboss Enterprise Application Platform, Redhat Jboss Enterprise Application Platform Expansion Pack, Redhat Process Automation and 2 more.
How do I fix CVE-2025-9784?
Upgrade io.undertow:undertow-core to a fixed version for your release line: 2.2.38.Final or 2.3.20.Final.
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-2025-9784 being exploited?
There is no known exploitation of CVE-2025-9784 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as CLSA-2026-1788890118, CLSA-2026-1789456491, DEBIAN-CVE-2025-9784, GHSA-95h4-w6j8-2rp8, UBUNTU-CVE-2025-9784.