What is CVE-2026-21513?
Protection mechanism failure in MSHTML Framework allows an unauthorized attacker to bypass a security feature over a network.
The record classifies CVE-2026-21513 under weakness class CWE-693. 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. 23 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 260 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 8.8 — HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H - EPSS (FIRST)
- 15.8% probability of exploitation in the next 30 days, higher than 96.8% of all scored CVEs
- CISA KEV
- Listed since 2026-02-10, federal remediation deadline 2026-03-03
- Threadlinqs priority
- 9/10 — CISA KEV-listed, which Threadlinqs floors at 9
- Published
- 2026-02-10, last modified 2026-08-19
Is CVE-2026-21513 being exploited?
CISA added CVE-2026-21513 to the Known Exploited Vulnerabilities catalog on 2026-02-10, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2026-03-03 under BOD 22-01. Weaponised exploit code for CVE-2026-21513 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 57 in the Threadlinqs vulnerability feed.
- trickest/cve (trickest)
Affected products and versions
- Microsoft: Windows 10 1607, Windows 10 1809, Windows 10 21h2, Windows 10 22h2, Windows 11 23h2, Windows 11 24h2, Windows 11 25h2, Windows Server 2012, Windows Server 2012 r2, Windows Server 2016, Windows Server 2019, Windows Server 2022, Windows Server 2022 23h2, Windows Server 2025
Showing 14 of 23 recorded product entries.
How to fix CVE-2026-21513
Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21513. Because CVE-2026-21513 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2026-03-03. 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-2026-21513
7 tracked threats in the Threadlinqs corpus reference CVE-2026-21513, either in the campaign’s CVE list or as an indicator on the campaign record.
- Exposed Server Reveals AI-Assisted WebDAV Phishing Kit Targeting Mexican Users (CVE-2025-33053) — HIGH · 2026-07-20
- CVE-2026-32202 — Windows Shell Protection Mechanism Failure: NTLM Authentication Coercion via Auto-Parsed LNK Files (CISA KEV) — CRITICAL · 2026-04-29
- APT28 Router DNS Hijacking for Adversary-in-the-Middle Credential Theft — HIGH · 2026-04-07
- Pawn Storm (APT28) Deploys PRISMEX Malware Suite via CVE-2026-21509 and CVE-2026-21513 Zero-Days Targeting Ukrainian Defense Supply Chain — CRITICAL · 2026-03-25
- Microsoft MSHTML Remote Code Execution Zero-Day (CVE-2026-21513) — CRITICAL · 2026-03-04
- February 2026 Patch Tuesday: Six Zero-Days Among 59 CVEs — CrowdStrike-Discovered RDP EoP Exploited Since December 2025 — CRITICAL · 2026-02-12
- February 2026 Patch Tuesday: Six Zero-Days Among 59 CVEs — CRITICAL · 2026-02-12
Sources
Enriched from CVE.org, FIRST EPSS, CISA KEV, public proof-of-concept repositories. Last verified by Threadlinqs on .