Critical [CVE-2025-12543] Undertow HTTP Server Fails to Reject Malformed Host Headers Leading to Potential Cache Poisoning and SSRF
This critical-severity Red Hat Linux advisory covers CVE-2025-12543 affecting Red Hat JBoss Enterprise Application Platform 7.1 EUS for RHEL 7, Red Hat JBoss Enterprise Application Platform 7.3 EUS for RHEL 7, Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7.
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Summary
Undertow HTTP Server Fails to Reject Malformed Host Headers Leading to Potential Cache Poisoning and SSRF. Red Hat rates this important (CVSS 9.6).
Weakness: CWE-20. Affected package(s): eap8-wildfly, eap8-undertow, eap8-apache-cxf, eap8-wildfly-clustering, eap8-bouncycastle, eap7-undertow.
Resolved in Red Hat advisory RHSA-2026:3889 — update the affected packages (`sudo dnf update`).
Affected products named by the advisory: Red Hat JBoss Enterprise Application Platform 7.1 EUS for RHEL 7; Red Hat JBoss Enterprise Application Platform 7.3 EUS for RHEL 7; Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7; Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 8; and 11 more.
- eap8-wildfly-0:8.1.3-4.GA_redhat_00006.1.el8eap
- eap8-undertow-0:2.3.20-2.SP4_redhat_00001.1.el9eap
- eap8-apache-cxf-0:4.0.10-1.redhat_00001.1.el8eap
- eap8-wildfly-clustering-0:5.0.12-1.Final_redhat_00001.1.el9eap
- eap8-bouncycastle-0:1.82.0-1.redhat_00001.1.el9eap
- eap7-undertow-0:1.4.18-21.SP19_redhat_00001.1.ep7.el7
- eap8-jaxb-0:4.0.6-1.redhat_00001.1.el8eap
- eap8-wildfly-elytron-0:2.6.6-1.Final_redhat_00001.1.el8eap
- eap8-undertow-0:2.3.23-1.SP3_redhat_00001.1.el8eap
- eap8-jboss-el-api_5.0_spec-0:4.0.2-1.Final_redhat_00001.1.el8eap
- eap8-wildfly-javadocs-0:8.1.1-4.GA_redhat_00007.1.el8eap
- io.undertow/undertow-core:2.2.39.Final-redhat-00001
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
- RHSA-2026:3889
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation checklist
- Update the affected package(s) to the fixed version shipped in RHSA-2026:3889 (`sudo dnf update` / `yum update`).
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
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