Public proof of conceptFix available

CVE-2018-8420

A public proof of concept exists; no exploitation attested.

Published2018-09-13
WeaknessCWE-611

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

A remote code execution vulnerability exists when the Microsoft XML Core Services MSXML parser processes user input, aka "MS XML Remote Code Execution Vulnerability." This affects Windows 7, Windows Server 2012 R2, Windows RT 8.1, Windows Server 2008, Windows Server 2012, Windows 8.1, Windows Server 2016, Windows Server 2008 R2, Windows 10, Windows 10 Servers.

Timeline

dates in UTC

2018-09-1300:29CVE publishedNVD
2026-10-2319:23First public proof of conceptPoC-in-GitHub
2026-10-2319:23EPSS crossed 10 %FIRST EPSS

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2018-8420?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2018-8420?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Microsoft windows 10

Branch	Affected	Fixed in	Source
—	all versions	no fix published	NVD
1607.x	= 1607	no fix published	NVD
1703.x	= 1703	no fix published	NVD
1709.x	= 1709	no fix published	NVD
1803.x	= 1803	no fix published	NVD

Microsoft windows server

Branch	Affected	Fixed in	Source
2008.x	= 2008	no fix published	NVD
2012.x	= 2012	no fix published	NVD
2016.x	= 2016	no fix published	NVD

Microsoft windows 7

Branch	Affected	Fixed in	Source
—	all versions	no fix published	NVD

1 more product in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

portal.msrc.microsoft.comPatch · Vendor Advisory

Detection

read 2026-10-23 19:23 UTC

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: 1 repository, unverifiedidkwim/CVE-2018-8420

Sources

NVDCVSS 3.08.8read 2026-10-23
NVDCVSS 2.09.3read 2026-10-23
NVDweakness (CWE)CWE-611read 2026-10-23
FIRST EPSSEPSS score48.9 %read 2026-10-23
PoC-in-GitHubproof of concept1read 2026-10-23

Technical details

CVSS v3 Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Published: 2018-09-13
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2018-8420?

Is CVE-2018-8420 actively exploited?

Active exploitation of CVE-2018-8420 has not been confirmed. Its EPSS score was 48.9% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2018-8420?

CVE-2018-8420 has a CVSS v3 base score of 8.8 (HIGH severity), with vector string CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

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