Threats / Microsoft / CVE-2018-8639
CVE-2018-8639
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Microsoft Windows vulnerability
Microsoft Windows Win32k improper resource shutdown vulnerability allows local authenticated attackers to escalate privileges and execute arbitrary kernel-mode code.
Verdict
Today item, not a backlog item.
A local privilege escalation flaw in Windows Win32k enables authenticated attackers to gain kernel-level code execution. Active exploitation and ransomware deployment have been observed in the wild.
CISA KEV Yes · 2025-03-034Ransomware use Flagged4EPSS 0.22349 (verify live)5Exploit Public PoC6CVSS 8.4 (CISA)3CISA SSVC Exploitation: active · Automatable: no · Impact: total3
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
6 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 2025-03-03), flagged for known ransomware use.
Probability (EPSS)
EPSS 0.22349 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 8.4 (CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) · Affected: Microsoft, Windows. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-404 CWE-404 — weakness family: Resource / availability.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: no · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 2273 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
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 gain initial access as an authenticated local user on a Windows system.
Business
Legitimate user credentials are compromised or an insider threat exists.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I exploit the Win32k resource handling flaw to escalate my privileges to kernel level.
Business
Security boundary between user and kernel mode is breached.
3
Lateral reach — past segmentation narrative 3
Attacker
I execute arbitrary code with kernel privileges to install malware or ransomware.
Business
System is fully compromised; ransomware deployment leads to data encryption and operational disruption.
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