CVE-2026-28367

Undertow: undertow: request smuggling via `\r\r\r` as a header block terminator

publishedCWE-444

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.

Technical severity8.7 highCVSS 3.1 · CNA: redhat

Published2026-03-27Source updated 2026-11-02

Collected2026-11-022 attributed sources

Fixes and workarounds

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

Affected products, source version ranges and reporting authorities
Product	Versions	Authority
Red Hat JBoss Enterprise Application Platform 8.1.6 Red Hat `io.undertow/undertow-core` https://access.redhat.com/downloads/content/package-browser/	≥ 2.3.24.SP2-redhat-00001; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 Red Hat `eap8-activemq-artemis` https://access.redhat.com/downloads/content/package-browser/	≥ 0:2.40.0-7.redhat_00015.1.el8eap; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 Red Hat `eap8-eap-product-conf-parent` https://access.redhat.com/downloads/content/package-browser/	≥ 0:801.6.1-1.GA_redhat_00001.1.el8eap; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 Red Hat `eap8-undertow` https://access.redhat.com/downloads/content/package-browser/	≥ 0:2.3.24-3.SP2_redhat_00001.1.el8eap; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8 Red Hat `eap8-wildfly` https://access.redhat.com/downloads/content/package-browser/	≥ 0:8.1.6-7.GA_redhat_00010.1.el8eap; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9 Red Hat `eap8-activemq-artemis` https://access.redhat.com/downloads/content/package-browser/	≥ 0:2.40.0-7.redhat_00015.1.el9eap; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9 Red Hat `eap8-eap-product-conf-parent` https://access.redhat.com/downloads/content/package-browser/	≥ 0:801.6.1-1.GA_redhat_00001.1.el9eap; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9 Red Hat `eap8-undertow` https://access.redhat.com/downloads/content/package-browser/	≥ 0:2.3.24-3.SP2_redhat_00001.1.el9eap; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9 Red Hat `eap8-wildfly` https://access.redhat.com/downloads/content/package-browser/	≥ 0:8.1.6-7.GA_redhat_00010.1.el9eap; < * (unaffected, rpm) Other versions: affected	CNA: redhat
Red Hat build of Apache Camel for Spring Boot 4 Red Hat `undertow-core` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: affected	CNA: redhat
Red Hat build of Apache Camel - HawtIO 4 Red Hat `undertow-core` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: unaffected	CNA: redhat
Red Hat Data Grid 8 Red Hat `undertow-core` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: affected	CNA: redhat
Red Hat Enterprise Linux 10 Red Hat `moditect` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: unaffected	CNA: redhat
Red Hat Enterprise Linux 8 Red Hat `pki-core:10.6/resteasy` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: unaffected	CNA: redhat
Red Hat Enterprise Linux 8 Red Hat `pki-deps:10.6/resteasy` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: unaffected	CNA: redhat
Red Hat Enterprise Linux 9 Red Hat `resteasy` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: unaffected	CNA: redhat
Red Hat Fuse 7 Red Hat `undertow-core` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 7 Red Hat `undertow-core` https://access.redhat.com/jbossnetwork/restricted/listSoftware.html	Range not reported Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8 Red Hat `org.jberet-jberet-parent` https://access.redhat.com/jbossnetwork/restricted/listSoftware.html	Range not reported Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform 8 Red Hat `undertow-core` https://access.redhat.com/jbossnetwork/restricted/listSoftware.html	Range not reported Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform Expansion Pack Red Hat `org.jberet-jberet-parent` https://access.redhat.com/jbossnetwork/restricted/listSoftware.html	Range not reported Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform Expansion Pack Red Hat `org.jboss.eap-jboss-eap-xp` https://access.redhat.com/jbossnetwork/restricted/listSoftware.html	Range not reported Other versions: affected	CNA: redhat
Red Hat JBoss Enterprise Application Platform Expansion Pack Red Hat `undertow-core` https://access.redhat.com/jbossnetwork/restricted/listSoftware.html	Range not reported Other versions: unaffected	CNA: redhat
Red Hat Process Automation 7 Red Hat `undertow-core` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: affected	CNA: redhat
Red Hat Single Sign-On 7 Red Hat `undertow-core` https://access.redhat.com/downloads/content/package-browser/	Range not reported Other versions: affected	CNA: redhat

Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.

CVSS assessments

CVSS scores, vectors and reporting authorities
Version / score	Vector	Authority
3.1 / 8.7 high	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N`	CNA: redhat

Exploit evidence

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

References

https://access.redhat.com/errata/RHSA-2026:25125CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:25126CNA: redhat · vendor-advisory, x_refsource_REDHAT
https://access.redhat.com/security/cve/CVE-2026-28367CNA: redhat · vdb-entry, x_refsource_REDHAT
https://bugzilla.redhat.com/show_bug.cgi?id=2443260CNA: redhat · issue-tracking, x_refsource_REDHAT

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