Description
A flaw was found in the Undertow HTTP server core, which is used in WildFly, JBoss EAP, and other Java applications. The Undertow library fails to properly validate the Host header in incoming HTTP requests.As a result, requests containing malformed or malicious Host headers are processed without rejection, enabling attackers to poison caches, perform internal network scans, or hijack user sessions.
Affected products
redhat: build of apache camel; redhat: data grid; redhat: fuse; redhat: jboss enterprise application platform; redhat: jboss enterprise application platform expansion pack; redhat: process automation; redhat: single sign-on; redhat: undertow
References10
- access.redhat.com/errata/RHSA-2026:0383 Vendor Advisory
- access.redhat.com/errata/RHSA-2026:0384 Vendor Advisory
- access.redhat.com/errata/RHSA-2026:0386 Vendor Advisory
- access.redhat.com/errata/RHSA-2026:3889 Vendor Advisory
- access.redhat.com/errata/RHSA-2026:3890 Vendor Advisory
- access.redhat.com/errata/RHSA-2026:3891 Vendor Advisory
- access.redhat.com/errata/RHSA-2026:3892 Vendor Advisory
- access.redhat.com/security/cve/CVE-2025-12543 Vendor Advisory
- bugzilla.redhat.com/show_bug.cgi?id=2408784 Issue TrackingVendor Advisory
- access.redhat.com/errata/RHSA-2026:0383 Vendor Advisory
Metrics
- CVSS 3.1
-
9.6
CRITICAL
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H - EPSS — exploit probability
- 1% percentile: 71 · as of 11 November 2026
- CWE
- CWE-20
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.