# CVE-2026-91920: Undertow: undertow: chunkreader message length permits chunk-size overflow

Status: published. Published: 2026-10-30. Updated: 2026-11-02.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Red Hat / Red Hat build of Apache Camel for Spring Boot 4 (undertow-servlet): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (pki-core:10.6/resteasy): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (pki-deps:10.6/resteasy): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (resteasy): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Fuse 7 (undertow-servlet): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 7 (jboss-eap-7/eap74-els-openjdk11-openshift-rhel8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 7 (jboss-eap-7/eap74-els-openjdk17-openshift-rhel8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 7 (jboss-eap-7/eap74-els-openjdk8-openshift-rhel8): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 7 (undertow-servlet): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8 (undertow-servlet): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform Expansion Pack (undertow-servlet): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Single Sign-On 7 (undertow-servlet): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 6.5 (medium); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.24% as of 2026-11-02; percentile 14.52%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-444

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/security/cve/CVE-2026-91920 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2528758 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-91920; retrieved 2026-11-02; source updated 2026-11-02

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-91920; retrieved 2026-11-02; source updated Not reported

Revision: ad5e6667dd04558f888b32b294b85d97cbb3913aa8d97106c57c4ba5f8006bdd

Canonical: https://y2.dev/cve/CVE-2026-91920

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