CVE-2018-8639: in the CISA KEV catalogue

Microsoft Windows Win32k Improper Resource Shutdown or Release Vulnerability. CISA added CVE-2018-8639 to the Known Exploited Vulnerabilities catalogue on 2025-03-03 with a default due date of 2025-03-24. Known ransomware campaign use: Known. Forensic triage flag: No.

Microsoft Windows Win32k contains an improper resource shutdown or release vulnerability that allows for local, authenticated privilege escalation. An attacker who successfully exploited this vulnerability could run arbitrary code in kernel mode. (CISA description)

Vendor / product: Microsoft Windows
CWE: CWE-404
CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
EPSS: 22%, percentile 97 (scored 2026-11-04)

EPSS puts about 22 in 100 odds (22%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 97% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.

Vendor and reference links (from CISA)

Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.

Data dates. CISA KEV catalogue version 2026.11.04, released 2026-11-04, 1,768 entries (checked 2026-11-04). EPSS model v2026.06.15, scored 2026-11-04, 400,189 CVEs. Sources: CISA and FIRST (EPSS by FIRST; scores generated by Empirical Security). Copied to our own database and refreshed automatically; if a refresh fails, the previous copy keeps serving with its own date.

Frequently asked questions

Is CVE-2018-8639 in the CISA KEV catalogue?

Yes. CISA added CVE-2018-8639 (Microsoft Windows Win32k Improper Resource Shutdown or Release Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2025-03-03. CISA's default due date for it is 2025-03-24.

Is CVE-2018-8639 used in ransomware attacks?

CISA marks known ransomware campaign use as Known for CVE-2018-8639.

What should I do about CVE-2018-8639?

CISA's required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Sources

CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
NVD record for CVE-2018-8639