Threats / Microsoft / CVE-2021-33771
CVE-2021-33771
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Microsoft Windows vulnerability
Microsoft Windows kernel vulnerability allowing privilege escalation via buffer overflow. Actively exploited in the wild with low EPSS score.
Verdict
Today item — known-exploited.
A kernel-level buffer overflow in Windows enables local attackers to escalate privileges. Active exploitation observed despite low predicted severity, indicating targeted or opportunistic use by threat actors.
01
Is it exploitable?
— the evidence, ranked above the scoreReported 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 2021-11-03).
Probability (EPSS)
EPSS 0.06204 — 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.
Weakness (CWE)
Mapped to CWE-119 Memory Buffer Bounds Error — weakness family: Memory safety.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
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 execute a local application or script that triggers the kernel buffer overflow condition.
Business
An attacker gains elevated system privileges on compromised endpoints, enabling lateral movement and persistence.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I leverage kernel-level access to disable security controls, install rootkits, or modify system behavior.
Business
Security monitoring and endpoint detection become ineffective; attackers operate with near-complete system control.
3
Lateral reach — past segmentation narrative 3
Attacker
I maintain persistence across reboots and evade user-mode defenses through kernel-mode operations.
Business
Incident response and remediation efforts are significantly complicated; full system rebuild may be required.
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