CVE-2025-9784: Undertow MadeYouReset HTTP/2 DDoS Vulnerability

September 2, 2025 (updated September 24, 2025)

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).

References

access.redhat.com/security/cve/CVE-2025-9784
bugzilla.redhat.com/show_bug.cgi?id=2392306
github.com/advisories/GHSA-95h4-w6j8-2rp8
github.com/undertow-io/undertow
github.com/undertow-io/undertow/pull/1778
issues.redhat.com/browse/UNDERTOW-2598
nvd.nist.gov/vuln/detail/CVE-2025-9784

Code Behaviors & Features

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