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Critical, CVSS 9.6

Undertow HTTP server core doesn't properly validate the Host header in incoming HTTP requests

CVE-2025-12543GHSA-j382-5jj3-vw4j

What to do

Partial vendor fix. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Maven io.undertow:undertow-core

    Affected
    >= 2.4.0.Alpha1, <= 2.4.0.Alpha1>= 2.3.0.Alpha1, < 2.3.21.Final< 2.2.39.Final
    Fixed in
    2.2.39.Final, 2.3.21.Final

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
9.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L
EPSS
  • CVE-2025-12543: 1.33% estimated exploitation activity in the next 30 days; percentile 71.16 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-j382-5jj3-vw4j

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2025-12543

Advisory: Undertow HTTP server core doesn't properly validate the Host header in incoming HTTP requests
IDs: CVE-2025-12543, GHSA-j382-5jj3-vw4j
Record: https://patchnext.com/advisories/cve-2025-12543 (revision 1, source checked 26 Oct 2026, 16:44 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: io.undertow:undertow-core 2.3.21.Final, 2.2.39.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.undertow:undertow-core: affected >= 2.4.0.Alpha1, <= 2.4.0.Alpha1; >= 2.3.0.Alpha1, < 2.3.21.Final; < 2.2.39.Final; fixed in 2.2.39.Final, 2.3.21.Final

## Suggested inspection (read-only)
- Maven io.undertow:undertow-core: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.undertow:undertow-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-j382-5jj3-vw4j (GitHub-reviewed advisory GHSA-j382-5jj3-vw4j lists affected ranges: Maven io.undertow:undertow-core >=2.4.0.Alpha1 =2.3.0.Alpha1 =0 <2.2.39.Final)

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