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

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.

Timeline

Scores

EPSS (exploitation in 30 days)

0.72% · top 46% of all CVEs (12 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.7.

Affected products

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1.6

  • unaffected 2.3.24.SP2-redhat-00001 – < *

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8

  • unaffected 0:2.40.0-7.redhat_00015.1.el8eap – < *

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8

  • unaffected 0:801.6.1-1.GA_redhat_00001.1.el8eap – < *

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8

  • unaffected 0:2.3.24-3.SP2_redhat_00001.1.el8eap – < *

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 8

  • unaffected 0:8.1.6-7.GA_redhat_00010.1.el8eap – < *

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9

  • unaffected 0:2.40.0-7.redhat_00015.1.el9eap – < *

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9

  • unaffected 0:801.6.1-1.GA_redhat_00001.1.el9eap – < *

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9

  • unaffected 0:2.3.24-3.SP2_redhat_00001.1.el9eap – < *

• Red Hat · Red Hat JBoss Enterprise Application Platform 8.1 for RHEL 9

  • unaffected 0:8.1.6-7.GA_redhat_00010.1.el9eap – < *

• Red Hat · Red Hat build of Apache Camel for Spring Boot 4

  All versions: affected

• Red Hat · Red Hat build of Apache Camel - HawtIO 4

  All versions: unaffected

• Red Hat · Red Hat Data Grid 8

  All versions: affected

• Red Hat · Red Hat Enterprise Linux 10

  All versions: unaffected

• Red Hat · Red Hat Enterprise Linux 8

  All versions: unaffected

• Red Hat · Red Hat Enterprise Linux 8

  All versions: unaffected

• Red Hat · Red Hat Enterprise Linux 9

  All versions: unaffected

• Red Hat · Red Hat Fuse 7

  All versions: affected

• Red Hat · Red Hat JBoss Enterprise Application Platform 7

  All versions: affected

• Red Hat · Red Hat JBoss Enterprise Application Platform 8

  All versions: affected

• Red Hat · Red Hat JBoss Enterprise Application Platform 8

  All versions: affected

• Red Hat · Red Hat JBoss Enterprise Application Platform Expansion Pack

  All versions: affected

• Red Hat · Red Hat JBoss Enterprise Application Platform Expansion Pack

  All versions: affected

• Red Hat · Red Hat JBoss Enterprise Application Platform Expansion Pack

  All versions: unaffected

• Red Hat · Red Hat Process Automation 7

  All versions: affected

• Red Hat · Red Hat Single Sign-On 7

  All versions: affected

Affected packages

From reviewed advisories of the GitHub Advisory Database.

• Mavenio.undertow:undertow-coreGHSA-3gv6-g396-9v4r (opens in a new tab)

What to do

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.

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-16694 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisory GHSA-3gv6-g396-9v4r (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-28367](https://cveledger.app/badge/CVE-2026-28367.svg)](https://cveledger.app/cve/CVE-2026-28367)

Record last updated 4 Nov 2026, 22:18 UTC.