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

Status: published. Published: 2026-03-27. Updated: 2026-11-02.

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.

## Remediation

- workaround: To mitigate this vulnerability, configure any proxy servers positioned in front of Undertow to strictly validate HTTP header terminations. Ensure that these proxies are configured to reject or normalize non-standard header block terminators, such as `\r\r\r`, before forwarding requests to Undertow. This operational control helps prevent request smuggling attacks by ensuring that only properly formed HTTP requests reach the Undertow server. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1.6 (io.undertow/undertow-core): ≥ 2.3.24.SP2-redhat-00001; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 (eap8-activemq-artemis): ≥ 0:2.40.0-7.redhat_00015.1.el8eap; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 (eap8-eap-product-conf-parent): ≥ 0:801.6.1-1.GA_redhat_00001.1.el8eap; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 (eap8-undertow): ≥ 0:2.3.24-3.SP2_redhat_00001.1.el8eap; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 (eap8-wildfly): ≥ 0:8.1.6-7.GA_redhat_00010.1.el8eap; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9 (eap8-activemq-artemis): ≥ 0:2.40.0-7.redhat_00015.1.el9eap; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9 (eap8-eap-product-conf-parent): ≥ 0:801.6.1-1.GA_redhat_00001.1.el9eap; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9 (eap8-undertow): ≥ 0:2.3.24-3.SP2_redhat_00001.1.el9eap; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9 (eap8-wildfly): ≥ 0:8.1.6-7.GA_redhat_00010.1.el9eap; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat build of Apache Camel for Spring Boot 4 (undertow-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat build of Apache Camel - HawtIO 4 (undertow-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Data Grid 8 (undertow-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10 (moditect): 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-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 7 (undertow-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8 (org.jberet-jberet-parent): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform 8 (undertow-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform Expansion Pack (org.jberet-jberet-parent): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform Expansion Pack (org.jboss.eap-jboss-eap-xp): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat JBoss Enterprise Application Platform Expansion Pack (undertow-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Process Automation 7 (undertow-core): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Single Sign-On 7 (undertow-core): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 8.7 (high); CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.72% as of 2026-11-02; percentile 53.88%

- SSVC: exploitation none; automatable no; technical impact total; 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/errata/RHSA-2026:25125 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:25126 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-28367 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2443260 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-28367; retrieved 2026-11-02; source updated 2026-11-02

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-28367; retrieved 2026-11-02; source updated Not reported

Revision: d549966cd3fa25a1edd21ae2bae0810a6d1a492f586cd1a1b4f2d09781733e36

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