Threats / Microsoft / CVE-2021-43226
CVE-2021-43226
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Microsoft Windows vulnerability
Microsoft Windows Common Log File System Driver privilege escalation vulnerability allowing local privileged attackers to bypass security mechanisms.
Verdict
Today item — known-exploited.
A local privilege escalation flaw in Windows CLFS driver enables authenticated attackers with initial system access to circumvent security controls, potentially leading to further system compromise.
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Public proof-of-concept exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
7 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2025-10-06).
Probability (EPSS)
EPSS 0.03072 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Microsoft, Windows. Confirm exact fixed builds in the vendor advisory.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I establish initial access to the target system with user-level or limited privileges.
Business
An insider or compromised account gains a foothold on enterprise infrastructure.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I exploit the CLFS driver vulnerability to escalate my privileges on the local system.
Business
Security boundaries between user and system contexts collapse, enabling unrestricted system modification.
3
Lateral reach — past segmentation narrative 3
Attacker
I bypass security mechanisms that normally restrict privileged operations.
Business
Endpoint detection and response controls become ineffective against attacker-initiated system changes.
4
Data at risk — exfiltration narrative 4
Attacker
I gain full system-level control to install malware, modify configurations, or exfiltrate data.
Business
Organizational data confidentiality, integrity, and system availability are compromised at scale.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05