libundertow-java: A flaw was found in the Undertow HTTP server core, which is used in WildFly, JBoss EAP, and other Java applications
CVE-2025-12543 is fixed in libundertow-java on 1 platform, first by libundertow-java 1.4.23-3ubuntu0.1~esm1, released January 7, 2026. It is not reported as exploited. Patch Radar priority: High.
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.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| libundertow-java · Ubuntu 18.04.6 LTS (bionic) | 1.4.23-3ubuntu0.1~esm1 | libundertow-java 1.4.23-3ubuntu0.1~esm1 | Jan 7, 2026 |
| libundertow-java · Ubuntu 20.04 LTS (focal) | 2.0.29-1ubuntu0.1~esm1 | libundertow-java 2.0.29-1ubuntu0.1~esm1 | Jan 7, 2026 |
| libundertow-java · Ubuntu 22.04.1 LTS (jammy) | 2.2.16-1ubuntu0.1~esm1 | libundertow-java 2.2.16-1ubuntu0.1~esm1 | Jan 7, 2026 |
| libundertow-java · Ubuntu 24.04.5 LTS (noble) | 2.3.8-2ubuntu0.1~esm1 | libundertow-java 2.3.8-2ubuntu0.1~esm1 | Jan 7, 2026 |
| libundertow-java · Ubuntu 26.04.1 LTS (resolute) | 2.3.20-1ubuntu1 | libundertow-java 2.3.20-1ubuntu1 | Jan 7, 2026 |
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