Undertow: undertow: request smuggling via `\r\r\r` as a header block terminator (CVE-2026-28367)

Undertow: undertow: request smuggling via `\r\r\r` as a header block terminator (CVE-2026-28367) | HOL Guard CVE

Why this deserves its current priority

CVSS is 8.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps io.undertow:undertow-parent (maven), io.undertow:undertow-parent (maven). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
io.undertow:undertow-parentmaven	<=2.3.23.Final	Not reported
io.undertow:undertow-parentmaven	>=0	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for io.undertow:undertow-parent, io.undertow:undertow-parent.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Mar 27, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 21, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Jun 11, 2026

Sources and claim methodology

Upstream source description

A flaw was found in Undertow. A remote attacker can exploit this vulnerability by sending `\r\r\r` as a header block terminator. This can be used for request smuggling with certain proxy servers, such as older versions of Apache Traffic Server and Google Cloud Classic Application Load Balancer, potentially leading to unauthorized access or manipulation of web requests.

Quoted source text, attributed separately from HOL analysis.