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VulnerabilityCVE-2026-20817Published 2026-01-13

CVE-2026-20817 — Microsoft Windows 10 Version 21H2

highPublic exploit4 PoC repos

As of 2026-07-30, CVE-2026-20817 is a HIGH-severity vulnerability in Microsoft Windows 10 Version 21H2, CVSS v3.1 7.8, EPSS 5.5% (92.5th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-20817, most recently “CVE-2026-20817: Windows Error Reporting Service (WerSvc.dll) Local Privilege Escalation via ALPC Argument Injection”.

CVSS v3.1
7.8/10High
EPSS
5.5%Higher than 92.5% of scored CVEs
CISA KEV
NoNot in the KEV catalog
Tracked threats
1Campaigns referencing it
Priority
9.6/10Threadlinqs triage score
Published
Updated 2026-07-30
CVSS v3.1 7.8 (HIGH) · EPSS 5.5% (higher than 92.5% of all scored CVEs) · Priority 9.6/10 · Published 2026-01-13

Last updated:

What is CVE-2026-20817?

Improper handling of insufficient permissions or privileges in Windows Error Reporting allows an authorized attacker to elevate privileges locally.

The record classifies CVE-2026-20817 under weakness class CWE-280. Its CVSS v3 base vector states that the flaw requires local access to the host, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 10 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 265 days ago.

Severity and exploitation probability

CVSS v3.1 base score
7.8 — HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
EPSS (FIRST)
5.5% probability of exploitation in the next 30 days, higher than 92.5% of all scored CVEs
CISA KEV
Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority
9.6/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published
2026-01-13, last modified 2026-07-30

Is CVE-2026-20817 being exploited?

Weaponised exploit code for CVE-2026-20817 is publicly available. 4 public proof-of-concept repositories are tracked for this identifier.

Affected products and versions

  • Microsoft: Windows 10 Version 21H2, Windows 10 Version 22H2, Windows 11 version 23H2, Windows 11 Version 23H2, Windows 11 Version 24H2, Windows 11 Version 25H2, Windows Server 2022, Windows Server 2022, 23H2 Edition (Server Core installation), Windows Server 2025, Windows Server 2025 (Server Core installation)

How to fix CVE-2026-20817

Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20817. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2026-20817

1 tracked threat in the Threadlinqs corpus references CVE-2026-20817, either in the campaign’s CVE list or as an indicator on the campaign record.

Sources

Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories, public proof-of-concept repositories. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.

Vendor advisory and patch