Threats / Microsoft / CVE-2021-31956
CVE-2021-31956
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Microsoft Windows vulnerability
Microsoft Windows NTFS contains an integer underflow or buffer overflow vulnerability enabling local privilege escalation through specially crafted applications.
Verdict
Today item — known-exploited.
This vulnerability allows local attackers to escalate privileges on Windows systems via malicious applications. The high EPSS score and active exploitation indicate significant risk to unpatched systems, particularly in multi-user or shared computing environments.
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
4 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 0.20268 — 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-191 Integer Underflow, CWE-787 Out-of-bounds Write — 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 craft a malicious application that triggers an integer underflow or buffer overflow in the NTFS driver.
Business
An attacker gains elevated system privileges, enabling full system compromise and data exfiltration.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I execute the application on a target Windows system where I have local user access.
Business
The organization loses control of affected systems and faces potential lateral movement to critical infrastructure.
3
Lateral reach — past segmentation narrative 3
Attacker
I use the elevated privileges to install persistent backdoors or access sensitive data.
Business
Remediation costs, forensic investigation, and potential regulatory penalties accumulate as the breach scope expands.
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