Medium · CVSS 6.5CVE-2026-91920

Undertow: undertow: chunkreader message length permits chunk-size overflowCVE-2026-91920

Answer in brief

CVE-2026-91920 records a Medium severity (CVSS 6.5) vulnerability in Undertow: undertow: chunkreader message length permits chunk-size overflow. The current sources do not mark it as known exploited. The current feed maps Red Hat/jboss-eap-7/eap74-els-openjdk11-openshift-rhel8 (generic), Red Hat/jboss-eap-7/eap74-els-openjdk17-openshift-rhel8 (generic), Red Hat/jboss-eap-7/eap74-els-openjdk8-openshift-rhel8 (generic), Red Hat/undertow-servlet (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 30, 2026Updated Oct 30, 2026Source checked Oct 30, 2026First seen by HOL Oct 30, 2026Material review Oct 30, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.5
Exploitation: Not marked as known exploited
Affected software: 4 mapped packages or products
Fix availability: Not reported

Why this deserves its current priority

CVSS is 6.5. 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 Red Hat/jboss-eap-7/eap74-els-openjdk11-openshift-rhel8 (generic), Red Hat/jboss-eap-7/eap74-els-openjdk17-openshift-rhel8 (generic), Red Hat/jboss-eap-7/eap74-els-openjdk8-openshift-rhel8 (generic), Red Hat/undertow-servlet (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Red Hat/jboss-eap-7/eap74-els-openjdk11-openshift-rhel8generic	*	Not reported
Red Hat/jboss-eap-7/eap74-els-openjdk17-openshift-rhel8generic	*	Not reported
Red Hat/jboss-eap-7/eap74-els-openjdk8-openshift-rhel8generic	*	Not reported
Red Hat/undertow-servletgeneric	*	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Red Hat/jboss-eap-7/eap74-els-openjdk11-openshift-rhel8, Red Hat/jboss-eap-7/eap74-els-openjdk17-openshift-rhel8, Red Hat/jboss-eap-7/eap74-els-openjdk8-openshift-rhel8.
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
Oct 30, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 30, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 30, 2026

Sources and claim methodology

Upstream source description

A flaw was found in the ChunkReader component of the Undertow web server, which is used to handle chunked transfer encoding in HTTP requests. The issue occurs because a security check for the chunk size is performed before the value is shifted, allowing a specifically crafted 15-digit chunk size to bypass the limit and overflow into internal state flags. This can cause the server to terminate a request body prematurely and interpret the remaining data as a separate, smuggled request.

Quoted source text, attributed separately from HOL analysis.