# CVE-2026-42993 — Microsoft Windows 10 Version 21H2

> As of 2026-06-23, CVE-2026-42993 is a HIGH-severity vulnerability in Microsoft Windows 10 Version 21H2, CVSS v3.1 7.5, EPSS 0.4% (34.6th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-42993, most recently “Microsoft June 2026 Patch Tuesday — 198+ CVEs Including CVE-2026-49160 (HTTP.sys 'HTTP/2 Bomb' DoS), CVE-2026-50507 (BitLocker 'YellowKey' Bypass) and CVE-2026-45586 (Collaborative Translation Framework EoP)”.

**Last updated:** 2026-06-23

## What is CVE-2026-42993?

Heap-based buffer overflow in Remote Desktop Client allows an unauthorized attacker to execute code over a network.

The record classifies CVE-2026-42993 under weakness class [CWE-122](https://cwe.mitre.org/data/definitions/122.html). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first, and has high impact on confidentiality, integrity, availability. 10 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 95 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 7.5 — HIGH (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **EPSS (FIRST):** 0.4% probability of exploitation in the next 30 days, higher than 34.6% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.1/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-06-09, last modified 2026-06-23

## Is CVE-2026-42993 being exploited?

No public exploitation evidence for CVE-2026-42993 is recorded in the sources Threadlinqs tracks — CISA KEV, Exploit-DB, public proof-of-concept repositories and ProjectDiscovery Nuclei — as of 2026-06-23. That is an absence of evidence in those feeds, not a guarantee that the vulnerability is unexploited.

## 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 11 version 26H1, Windows Server 2022, Windows Server 2025, Windows Server 2025 (Server Core installation)

## How to fix CVE-2026-42993

No vendor patch reference has been recorded for CVE-2026-42993 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-42993

1 tracked threat in the Threadlinqs corpus references CVE-2026-42993, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Microsoft June 2026 Patch Tuesday — 198+ CVEs Including CVE-2026-49160 (HTTP.sys 'HTTP/2 Bomb' DoS), CVE-2026-50507 (BitLocker 'YellowKey' Bypass) and CVE-2026-45586 (Collaborative Translation Framework EoP)](https://intel.threadlinqs.com/threat/TL-2026-0732) — HIGH · 2026-06-09

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-06-25.

**Vendor advisory and patch**

- [msrc.microsoft.com — vendor advisory](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42993)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-42993
Full detection coverage and IOCs for threats exploiting CVE-2026-42993 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp