CVE-2026-21509

ENISA EUVD: EUVD-2026-4666 ↗
Exploited in the Wild ✓ Confirmed 0-Day ★ Google Project Zero
Triaged: Feb. 18, 2026 6 articles Published: 2026-01-26
VulnLookup ↗ NVD ↗ EUVD ↗ MITRE ↗ Advisory ↗ P0 Sheet ↗ CISA KEV ↗

EPSS Score

Source: FIRST.org · 2026-05-23
11.44%
probability
This CVE has a 11.44% probability of being exploited in the next 30 days.
0% Top 93.7th percentile of all CVEs 100%

CVSS v3.1

Source: VulnerabilityLookup (CIRCL)
7.8
HIGH
Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Temporal
Exploit Code Maturity
Functional
Remediation Level
Official Fix
Report Confidence
Confirmed
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

Description

NVD
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

Affected Products

Microsoft
Microsoft 365 Apps for Enterprise
16.0.1
Microsoft
Microsoft Office 2016
16.0.0
Microsoft
Microsoft Office 2019
19.0.0
Microsoft
Microsoft Office LTSC 2021
16.0.1
Microsoft
Microsoft Office LTSC 2024
16.0.0

Google Project Zero

Patched
Jan. 26, 2026
Reported by
Google Threat Intelligence Group, Microsoft Threat Intelligence Center (MSTIC), Microsoft Security Response Center (MSRC), and Office Product Group Security Team

Signal Intelligence

Confidenceⓘ
92%
EPSS 11.44%
CVSS v3.1 7.8
Mentions 6
Last Seen Mar 02, 2026

CNA Information

CNA Assigner
microsoft
CNA Title
Microsoft Office Security Feature Bypass Vulnerability

Analyst Note

CVE-2026-21509 is confirmed as a zero-day with strong evidence: Microsoft issued out-of-band patches for active exploitation, it is tracked in Google Project Zero, and multiple credible sources (TheHackerNews, BleepingComputer) document active attacks by APT28. The HIGH CVSS score (7.8) and documented weaponization in espionage-focused campaigns further validate the threat severity.

Threat Actors 8

APT 28
apt_group Information theft and espionage 🇷🇺 RU
Vicious Panda
apt_group Information theft and espionage 🇨🇳 CN
APT35
apt_group Information theft and espionage 🇮🇷 IR
TAG-28
apt_group Information theft and espionage 🇨🇳 CN
Roaming Tiger
apt_group Information theft and espionage 🇨🇳 CN
TA2552
apt_group Information theft and espionage 🇮🇷 IR
White Bear
apt_group Information theft and espionage 🇷🇺 RU
Magic Kitten
apt_group Information theft and espionage 🇮🇷 IR

Triage Info

Decided atFeb 18, 2026
Published DateJan 26, 2026