Improper Validation of Syntactic Correctness of Input Affecting io.undertow:undertow-core package, versions [,2.2.39.Final)[2.3.0.Alpha1,2.3.21.Final)[2.4.0.Alpha1,2.4.0.Beta1)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
Do your applications use this vulnerable package?
In a few clicks we can analyze your entire application and see what components are vulnerable in your application, and suggest you quick fixes.
Test your applications- Snyk IDSNYK-JAVA-IOUNDERTOW-14908846
- published9 Jan 2026
- disclosed7 Jan 2026
- creditAhmet Artuç
Introduced: 7 Jan 2026
CVE-2025-12543 (opens in a new tab)How to fix?
Upgrade io.undertow:undertow-core to version 2.2.39.Final, 2.3.21.Final, 2.4.0.Beta1 or higher.
Overview
io.undertow:undertow-core is a Java web server based on non-blocking IO.
Affected versions of this package are vulnerable to Improper Validation of Syntactic Correctness of Input of the request's Host header. An attacker can manipulate server behavior, potentially leading to cache poisoning, internal network scanning, or session hijacking by sending crafted HTTP requests with malicious Host headers.