# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Sep 2025
- **Updated:** 14 Oct 2026
- **Also known as:** CLSA-2026-1788890118, CLSA-2026-1789456491, DEBIAN-CVE-2025-9784, GHSA-95h4-w6j8-2rp8, UBUNTU-CVE-2025-9784

## 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).

Weakness: CWE-404 (Improper Resource Shutdown or Release), CWE-770 (Allocation of Resources Without Limits or Throttling)

## 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 | Ecosystem | 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: 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, Redhat Single Sign-On, Redhat Undertow.

## 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.

## 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:

- https://github.com/drackyjr/CVE-2025-9784 (github_poc): https://github.com/drackyjr/CVE-2025-9784

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-9784 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2025-9784 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.undertow:undertow-core (Maven): affected all versions; fixed in 2.2.38.Final
- io.undertow:undertow-core (Maven): affected all versions; fixed in 2.2.38.Final
- io.undertow:undertow-core (Maven): affected from 2.3.0.Alpha1; fixed in 2.3.20.Final
- io.undertow:undertow-core (Maven): affected from 2.3.0.Alpha1; fixed in 2.3.20.Final

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-9784/ (Markdown: https://insights.sbomify.com/CVE-2025-9784/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-9784
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-9784
- OSV: https://osv.dev/vulnerability/CVE-2025-9784

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-9784/
Summaries are generated and may contain mistakes; the official description above is the record.