CVE-2026-21509

ENISA EUVD: EUVD-2026-4666 ↗
Exploited in the Wild ✓ Confirmed 0-Day ★ Google Project Zero
Triaged: Feb. 18, 2026 7 articles
VulnLookup ↗ NVD ↗ EUVD ↗ MITRE ↗ Advisory ↗ P0 Sheet ↗ CISA KEV ↗

EPSS Score

Source: FIRST.org · 2026-05-24
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: NVD
7.8
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

Project Zero
Microsoft Office Security Feature Bypass Vulnerability

Affected Products

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

Exploits & PoC

suuhm/CVE-2026-21509-handler

PowerShell script to check, apply, and test the Kill-Bit protection for the CVE-2026-21509 Microsoft Office zero-day vulnerability affecting Office 20

7
DameDode/CVE-2026-21509-POC

POC for the Office vulnerability

0
2 repos — triés par ⭐ Rechercher sur GitHub ↗

Signal Intelligence

Confidenceⓘ
92%
EPSS 11.44%
CVSS v3.1 7.8
Mentions 7
Last Seen Jun 02, 2026

CNA Information

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