Critical severity · published Jan 7, 2026
CVE-2025-12543
Undertow-core: undertow http server fails to reject malformed host headers leading to potential cache poisoning and ssrf
9.6
CVSS
1.3%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
High
Integrity
High
Availability
High
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)1.3% · higher than 71% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
RB
RHEL-8 based Middleware Containers · Red Hat
All versions, or not specified · source: vendor
RH
Red Hat Data Grid 8 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat Fuse 7 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 7 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 7.1 EUS for RHEL 7 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 7.3 EUS for RHEL 7 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 7 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 8 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 7.4 ELS on RHEL 9 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 7.4.24 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 8.0 for RHEL 8 · Red Hat
All versions, or not specified · source: vendor, CISA
RH
Red Hat JBoss Enterprise Application Platform 8.0 for RHEL 9 · Red Hat
All versions, or not specified · source: vendor, CISA
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-12543
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-12543
vendor-advisory
https://access.redhat.com/errata/RHSA-2026:0383
vendor-advisory
https://access.redhat.com/errata/RHSA-2026:0384
vendor-advisory
https://access.redhat.com/errata/RHSA-2026:0386
vendor-advisory
https://access.redhat.com/errata/RHSA-2026:33371
vendor-advisory
https://access.redhat.com/errata/RHSA-2026:33372
vendor-advisory
https://access.redhat.com/errata/RHSA-2026:3889
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