CVE-2025-12543
January 07, 2026
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.
Affected Packages
https://github.com/undertow-io/undertow.git (GITHUB):
Affected version(s) >=2.3.0.Final <2.3.21.FinalFix Suggestion:
Update to version 2.3.21.Finalhttps://github.com/undertow-io/undertow.git (GITHUB):
Affected version(s) >=1.0.0.Alpha1 <2.2.39.FinalFix Suggestion:
Update to version 2.2.39.Finalhttps://github.com/undertow-io/undertow.git (GITHUB):
Affected version(s) =2.4.0.Alpha1 <2.4.0.Beta1Fix Suggestion:
Update to version 2.4.0.Beta1io.undertow:undertow-core (JAVA):
Affected version(s) >=1.0.0.Alpha1 <2.2.39.FinalFix Suggestion:
Update to version 2.2.39.Finalio.undertow:undertow-core (JAVA):
Affected version(s) >=2.3.0.Alpha1 <2.3.21.FinalFix Suggestion:
Update to version 2.3.21.FinalRelated Resources (20)
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Contact UsCVSS v4
Base Score:
9.4
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
PASSIVE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
LOW
Subsequent System Confidentiality
HIGH
Subsequent System Integrity
HIGH
Subsequent System Availability
LOW
CVSS v3
Base Score:
9.6
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
LOW
Weakness Type (CWE)
Improper Input Validation
EPSS
Base Score:
0.15
