Widely used Undertow-based servers (WildFly/JBoss EAP) with high impact on data integrity and sessions; critical to many enterprises.
CVE-2025-12543
Undertow hostname header validation flaw enables cache poisoning and session hijack.
Is CVE-2025-12543 being exploited?
Not confirmed. CVE-2025-12543 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 1.4% probability of exploitation in the next 30 days.
How severe is CVE-2025-12543?
CVE-2025-12543 is rated Critical with a CVSS score of 9.6. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2025-12543?
Yes. A fix has been recorded for CVE-2025-12543. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2025-12543 affect?
CVE-2025-12543 affects Undertow, WildFly, JBoss EAP, Java apps using Undertow. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2025-12543?
Patch ASAP when available; monitor exploitation; harden Host header handling.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Attacker can poison caches, perform internal network scans, or hijack user sessions via crafted Host header.
Immediate action required