Undertow HTTP server core doesn't properly validate the Host header in incoming HTTP requests
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.
This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. A user must be tricked into taking some action. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality high, integrity high, availability low.
The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L
CVE-2025-12543 is classified as CWE-20: Improper Input Validation. The application accepts input without checking that it has the expected form, so malformed values reach code that assumes they are well formed.
CVE-2025-12543 is recorded against 9 packages.
Published on 7 January 2026 and last revised on 19 August 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.
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These advisories are the same class of weakness (CWE-20: Improper Input Validation) in other software:
Each distribution ships its own build and its own fixed version. Pick the one you run:
Details
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L
Affected Packages
| Software | From version | Fixed in |
|---|---|---|
| build-of-apache-camel | — | 4.14.4 |
| data-grid | — | — |
| fuse | — | — |
| io.undertow:undertow-core | — | 2.2.39.Final |
| jboss-enterprise-application-platform | — | — |
| jboss-enterprise-application-platform-expansion-pack | — | — |
| process-automation | — | — |
| single-sign-on | — | — |
| undertow | 2.3.0 | 2.3.21 |
References
Similar Threats
Exploit Protection
CVE-2025-12543 carries CVSS 9.6 Critical rating. BotEraser checks your installation against this and other known CVE records, and blocks IPs associated with exploit activity.
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