CVE-2021-40444: Microsoft MSHTML RCE via ActiveX
Summary
Microsoft Office allows remote code execution via MSHTML component loading crafted ActiveX controls (Follina predecessor).
Why It Matters
CRITICAL severity — known to be exploited in the wild（CISA KEV）；action required: Apply updates per vendor instructions. ；affects Microsoft Office 2019, Microsoft Office 2016, Microsoft Office 2013 and more.
Current Status
- Vulnerability status: Known exploited (CISA KEV)
- Last intelligence update: 2026-10-27 · source: NVD
- CISA KEV added: 2021-11-03 · remediation deadline: 2021-11-17
Entity Activity Timeline
- 2021-11-03 — Added to CISA KEV as known-exploited · action: Apply updates per vendor instructions.
- 2021-09-15 — NVD publication / disclosure
- 2026-10-27 — Intelligence record updated（NVD sync）
Severity
CRITICAL
CVSS Score: 8.8
AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
Known Exploited (CISA KEV)
Known Exploited Vulnerability
Added: 2021-11-03 · Remediation deadline: 2021-11-17
Apply updates per vendor instructions.
Source Attribution
Source: NVD · Updated: 2026-10-27T00:00:00.000 · Confidence: high
Impact
Based on CVSS vector: AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H — assess confidentiality, integrity, and availability impact via the official vector documentation.
Affected Software
- Microsoft Office 2019 (Unknown)
- Microsoft Office 2016 (Unknown)
- Microsoft Office 2013 (Unknown)
- Microsoft 365 Apps for Enterprise (Unknown)
Fix
Upgrade affected software to the fixed version identified above. Apply vendor patches and monitor advisories before exposed systems go unpatched.
Sources & Evidence
Export threat intelligence
Download an OASIS STIX 2.1 threat-intelligence bundle (JSON) for MISP / OpenCTI / TAXII import
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