CVE-2025-12543
Undertow-core: undertow http server fails to reject malformed host headers leading to potential cache poisoning and ssrf
- Published
- Jan 7, 2026
- Updated
- Sep 7, 2026
- Assigning CNA
- redhat
- Evidence observed
- Aug 8, 2026
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:LLow · next 30 days
- Percentile
- 69.9%
- Model date
- Sep 21, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
Summary
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.
Sources
1Docker base image with backported Host header validation fix for CVE-2025-12543 in Undertow 1.4.x, enabling secure deployment of WildFly 11 applications.
Responsible use
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