Undertow MadeYouReset HTTP/2 DDoS Vulnerability
CVE: CVE-2025-9784
Component: undertow
CWE: CWE-770
Severity: Important
CVSS v3: 7.5/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Release date: 2025-09-01T06:21:54.614000+00:00

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).

Statement: 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 scripting) to exploitation, which directly impacts service availability. The vulnerability arises from an implementation weakness in HTTP/2 stream reset handling — malformed client requests can trigger server-side resets without incrementing abuse counters, allowing an attacker to bypass built-in request throttling and overhead limits. Since these resets consume CPU and memory resources and can be generated at scale over a single TCP/TLS connection, a remote attacker could exhaust server capacity quickly, impacting all legitimate clients.

Remediation:
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying the update, make sure all previously released errata relevant to your system have been applied. Also, back up your existing installation, including all applications, configuration files, databases and database settings. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
Before applying this update, make sure all previously released errata
relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258
No mitigation is currently available that meets Red Hat Product Security’s standards for usability, deployment, applicability, or stability.