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.
CVE-2025-12543
“—” beside the score: it is equal to NVD's CVSS score.
This critical-severity CVE scores 9.6 under NVD CVSS v3. EPSS exploit probability: 1.3% (70th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.
- CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
A fix is available — apply it.
- CVSS v3
- 9.6
- EG Score
- 9.6CRITICALmedium confidence
- EG Risk
- 59EG Risk 59/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity96% × 45%Impact severity (EG Severity): CVSS 9.6 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation40% × 40%EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.Automatability0% × 15%CISA's SSVC Automatable value: no (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at low, Track* at medium and Attend at high mission impact.Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high. - EPSS PROB
- 1.3%
- EPSS %ILE
- 70th
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (9.6): severity, escalated by confirmed exploitation. This CVE's 9.6 is its impact severity (EG Severity), not escalated.
- EG Severity
- 9.6 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
- EG Likelihood
- 1.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-19). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track* at medium mission impactTrack at low, Track* at medium and Attend at high mission impact.CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low, Track* at medium and Attend at high mission impact.
A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
January 7, 2026
Last Modified
October 14, 2026
Advisory Details (12)
Auto-updated Oct 7, 2026Affected: Red Hat Enterprise Linux 7. Red Hat Product Security has rated this update as having a security impact of Important. A Common
https://access.redhat.com/errata/RHSA-2026:4915Affected: Red Hat Enterprise Linux 9. Red Hat Product Security has rated this update as having a security impact of Important. A Common
https://access.redhat.com/errata/RHSA-2026:3891Affected: Red Hat Enterprise Linux 8. Red Hat Product Security has rated this update as having a security impact of Important. A Common
https://access.redhat.com/errata/RHSA-2026:3889Affected: Red Hat Enterprise Linux 7.
https://access.redhat.com/errata/RHSA-2026:33372Affected: Red Hat Enterprise Linux 7. Red Hat Product Security has rated this update as having a security impact of Important. A Common
https://access.redhat.com/errata/RHSA-2026:33371Affected: Red Hat Enterprise Linux 8.
https://access.redhat.com/errata/RHSA-2026:0386Affected: Red Hat Enterprise Linux 9. Red Hat Product Security has rated this update as having a security impact of Important. A Common
https://access.redhat.com/errata/RHSA-2026:0384Affected: Red Hat Enterprise Linux 8. Red Hat Product Security has rated this update as having a security impact of Important. A Common
https://access.redhat.com/errata/RHSA-2026:0383Affected: Red Hat Enterprise Linux 9. Red Hat Product Security has rated this update as having a security impact of Important. A Common
https://access.redhat.com/errata/RHSA-2026:4917Affected: Red Hat Enterprise Linux 8. Red Hat Product Security has rated this update as having a security impact of Important. A Common
https://access.redhat.com/errata/RHSA-2026:4916Vendor Advisories for CVE-2025-12543(18)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- RHSA-2026:76128Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 7
- RHSA-2026:76130Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 9
- RHSA-2026:76129Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update on RHEL 8
- RHSA-2026:76134Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 for OpenShift image security update
- RHSA-2026:76132Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Single Sign-On 7.6.13 security update
- RHSA-2026:33371Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat JBoss Enterprise Application Platform 7.3.18 security update
- RHSA-2026:33372Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat JBoss Enterprise Application Platform 7.1.15 security update
- RHSA-2026:4924Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat JBoss Enterprise Application Platform 7.4.24 security update
- +10 more
Patch Availability(17)
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(2 across 2 ecosystems)
Debian:14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| undertow | 1.3.11-1 ... 2.3.8-2 (56 versions) |
| — |
Maven(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| io.undertow:undertow-core | 1.0.0.Alpha1 ... 2.2.9.Final (307 versions) |
| — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Additional Vendor Advisories
(1)
Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.
Data Freshness Timeline
(refreshed 23× in last 7d / 57× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.
Showing the most recent 98 of 228 refreshes on record for this CVE.
A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 2 repeat rows among the latest 100 are merged into the row they repeat. The 130 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-10-20 04:57 UTCEG score recompute
- 2026-10-20 04:57 UTCVendor advisory
- 2026-10-19 16:30 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-19 03:46 UTCEG score recompute
- 2026-10-19 03:46 UTCVendor advisory
- 2026-10-18 16:30 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-18 05:51 UTCEG score recompute
- 2026-10-18 02:35 UTCEG score recompute
- 2026-10-18 02:35 UTCVendor advisory
- 2026-10-17 16:32 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-17 01:27 UTCEG score recompute
- 2026-10-17 01:27 UTCVendor advisory
- 2026-10-16 16:37 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-16 00:18 UTCEG score recompute
- 2026-10-16 00:18 UTCVendor advisory
- 2026-10-15 16:30 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-14 17:29 UTCVendor advisory
- 2026-10-14 16:46 UTCEG score recompute
- 2026-10-14 16:46 UTCVendor advisory
- 2026-10-14 16:31 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-14 14:49 UTCEG score recompute
- 2026-10-14 14:49 UTCVendor advisory
- 2026-10-13 16:31 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-13 13:37 UTCVendor advisory
- 2026-10-12 17:25 UTCEG score recompute
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- 2026-10-12 16:32 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-12 12:26 UTCVendor advisory
- 2026-10-11 20:55 UTCEG score recompute
- 2026-10-11 19:05 UTCEG score recompute
- 2026-10-11 15:46 UTCEG score recompute
- 2026-10-11 13:46 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-10 19:58 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-09 20:06 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-08 17:08 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-07 23:46 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-06 17:20 UTCVendor advisory
- 2026-10-06 17:13 UTCVendor advisory
- 2026-10-06 16:52 UTCEG score recompute
- 2026-10-06 16:52 UTCVendor advisory
- 2026-10-06 15:16 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-06 12:28 UTCVendor advisory
- 2026-10-06 11:50 UTCVendor advisory
- 2026-10-06 00:26 UTCVendor advisory
- 2026-10-05 23:38 UTCEG score recompute
- 2026-10-05 23:38 UTCVendor advisory
- 2026-10-05 17:42 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-04 23:21 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-03 14:24 UTCEPSS rescoreEPSS 1.3% · 70th percentile
- 2026-10-01 19:48 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-30 15:02 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-28 13:50 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-27 04:45 UTCOSV refresh
- 2026-09-26 15:57 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-24 14:02 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-23 13:46 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-22 14:47 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-20 20:14 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-18 19:27 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-16 14:06 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-16 05:13 UTCEPSS rescoreEPSS 1.4% · 70th percentile
- 2026-09-15 03:08 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-13 16:45 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-12 14:59 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-11 14:51 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-11 09:35 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-10 09:33 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-08 21:59 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-07 16:00 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-07 14:07 UTCEG score recompute
- 2026-09-07 14:07 UTCVendor advisory
- 2026-09-06 13:46 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-04 20:30 UTCVendor advisory
- 2026-09-04 20:05 UTCEG score recompute
- 2026-09-04 20:05 UTCVendor advisory
- 2026-09-04 13:59 UTCEPSS rescoreEPSS 1.4% · 69th percentile
- 2026-09-04 05:05 UTCEPSS rescoreEPSS 1.2% · 66th percentile
- 2026-09-02 14:10 UTCEPSS rescoreEPSS 1.2% · 66th percentile
- 2026-09-01 13:52 UTCEPSS rescoreEPSS 1.2% · 66th percentile
- 2026-09-01 04:38 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-30 19:16 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-30 01:21 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-28 21:40 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-27 14:24 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-26 14:45 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-25 13:47 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-24 14:15 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-23 00:18 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-21 23:48 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-20 22:54 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-19 17:02 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-19 12:28 UTCVendor advisory
- 2026-08-19 12:12 UTCVendor advisory
- 2026-08-19 08:21 UTCVendor advisory
- 2026-08-19 07:49 UTCEG score recompute
- 2026-08-19 07:49 UTCVendor advisory
- 2026-08-18 13:47 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-17 13:46 UTCEPSS rescoreEPSS 1.2% · 65th percentile
- 2026-08-16 14:55 UTCEPSS rescoreEPSS 1.2% · 65th percentile
Related CVEs(same product + same vendor + same CWE)
Same product
10 shownMaven:io.undertow:undertow-core
Same vendor
10 shownredhat:RHSA-2026:0383 · redhat:RHSA-2026:4915 · redhat:RHSA-2026:76128
Frequently asked(5)
What is CVE-2025-12543?
When was CVE-2025-12543 made public?
Is CVE-2025-12543 actively exploited?
What is the CVSS score of CVE-2025-12543?
How do I remediate CVE-2025-12543?
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2025-12543
Is Your Infrastructure Affected by CVE-2025-12543?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.