CVE-2025-12543: Undertow HTTP server core doesn't properly validate the Host header in incoming HTTP requests
(updated )
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.
References
- access.redhat.com/errata/RHSA-2026:0383
- access.redhat.com/errata/RHSA-2026:0384
- access.redhat.com/errata/RHSA-2026:0386
- access.redhat.com/security/cve/CVE-2025-12543
- bugzilla.redhat.com/show_bug.cgi?id=2408784
- github.com/advisories/GHSA-j382-5jj3-vw4j
- github.com/undertow-io/undertow
- github.com/undertow-io/undertow/pull/1857
- github.com/undertow-io/undertow/pull/1860
- github.com/undertow-io/undertow/releases/tag/2.3.21.Final
- nvd.nist.gov/vuln/detail/CVE-2025-12543
Code Behaviors & Features
Detect and mitigate CVE-2025-12543 with GitLab Dependency Scanning
Secure your software supply chain by verifying that all open source dependencies used in your projects contain no disclosed vulnerabilities. Learn more about Dependency Scanning →