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CVE-2025-12543 Undertow

Affected softwareUndertow
Severity9.6 Critical CVSS 3.1 3 scores
Fixed in2.3.21.Final, 2.2.39.Final
WeaknessImproper input validation (CWE-20)
Published7 Jan 2026
Updated4 Nov 2026

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.

Exploitation status

Proof of concept only

A proof of concept exists, but no reviewed exploit catalogue lists this CVE.

  • CISA KEV not listed
  • VulnCheck KEV not listed
  • CISA Vulnrichment exploitation: poc CISA recorded that an exploit has been demonstrated. Automatable: no, technical impact: total.
  • Indexed PoC none indexed
  • EPSS 1.3% chance in 30 days

Waratek protection

No exploit published

Within Waratek scope. In the sources we check, nobody has published exploit code for this CVE or reported it being exploited.

A public code fix exists: undertow-io/undertow #1860.

  • Protection none
  • Action unverified
  • Review automated Upstream data
  • Record active
Decided by Exploit code for this candidate, published in a reviewed catalogue or a GitHub repository with 5 or more stars, or in use per CISA or VulnCheck; not only a CISA verdict, a forecast, or nothing at all
Finding This CVE is not listed in CISA KEV or VulnCheck KEV, CISA Vulnrichment records no active exploitation, no reviewed exploit catalogue carries an entry for it, and no GitHub PoC repository for it has 5 or more stars. Nobody has published exploit code worth tracing, so it is not a candidate for a rule ahead of the ones where somebody has; an upstream fix path does exist, so the remediation half of the candidacy still holds. This is a statement about what has been published, not about whether the defect is reachable or serious.
Candidate fix https://bugzilla.redhat.com/show_bug.cgi?id=2408784 : a Red Hat bug: the triage, which links onward to the fix

CVSS

9.6 CRITICAL v3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L 3 metrics

We show the highest score from the newest CVSS version. Scores from different versions can't be compared, and the first score listed is sometimes a 0.0 placeholder.

VersionScoreBandVectorAssignerType
CVSS 3.1 9.6 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L secalert@redhat.com Secondary published
CVSS 3.1 9.6 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H NVD Primary
CVSS 3.1 9.6 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L redhat-SADP Secondary

Affected software and releases

Oracle advisories

AdvisoryTypeQuarterProducts Oracle names in its risk matrix
Oracle Critical Patch Update April 2026 ↗ CPU 2026-Q2 Oracle Communications / Alarms, KPI, and Measurements (Undertow) (25.1.200)
Oracle Communications / Install (Undertow) (25.1.100, 25.1.200)

Oracle components and versions

FamilyComponentVersions, as Oracle lists themRead as
Oracle Communications Alarms, KPI, and Measurements (Undertow) 25.1.200 25.1.200
Oracle Communications Install (Undertow) 25.1.100, 25.1.200 25.1.100 · 25.1.200

Maven packages

Affected and fixed versions, from OSV.dev
PackageIntroducedFixedLast affected
io.undertow:undertow-core unspecified none unbounded
io.undertow:undertow-core 2.3.0.Alpha1 2.3.21.Final unbounded
io.undertow:undertow-core 0 2.2.39.Final unbounded

Products and versions

9 products, 15 version entries
SourceVendorProductSchemeAffected versions
osv io.undertow undertow-core generic any version · < 2.2.39 · ≥ 2.3.0 and < 2.3.21
nvd redhat build of apache camel generic < 4.14.4
nvd redhat data grid generic 8.0
nvd redhat fuse generic 7.0.0
nvd redhat jboss enterprise application platform generic any version · 7.0.0 · ≥ 8.0 and < 8.0.12 · ≥ 8.1.0 and < 8.1.3
nvd redhat jboss enterprise application platform expansion pack generic any version
nvd redhat process automation generic 7.0
nvd redhat single sign-on generic 7.0
nvd redhat undertow generic < 2.2.39 · ≥ 2.3.0 and < 2.3.21

References

URLTags
https://bugzilla.redhat.com/show_bug.cgi?id=2408784 bugzilla
https://github.com/undertow-io/undertow/pull/1860 WEB
https://github.com/undertow-io/undertow/pull/1857 WEB
https://issues.redhat.com/browse/UNDERTOW-2656 WEB
https://github.com/undertow-io/undertow/releases/tag/2.3.21.Final WEB
https://github.com/undertow-io/undertow/releases/tag/2.2.39.Final WEB
https://github.com/undertow-io/undertow PACKAGE
https://access.redhat.com/security/cve/CVE-2025-12543 WEB
https://access.redhat.com/errata/RHSA-2026:4924 WEB
https://access.redhat.com/errata/RHSA-2026:4917 WEB

Timeline

Published2026-01-07By the CVE Program.
NVD record modified2026-11-04NVD's own last-modified date for this record.