Microsoft Win32k Privilege Escalation Vulnerability
CVE-2019-0859 is a security vulnerability in Microsoft Win32k, added to CISA KEV on November 3, 2021. Patch priority: Plan to patch.
What it is
Microsoft Win32k fails to properly handle objects in memory causing privilege escalation. Successful exploitation allows an attacker to run code in kernel mode.
VulnCheck tracked exploitation 962 days before CISA's KEV listing. VulnCheck's broader catalog of in-the-wild exploitation evidence picked this up before it landed on CISA's formal list. Per-CVE fact about this entry; not a population claim about lead time in general.
Who's affected
Affects anyone running Microsoft Win32k. Microsoft products in a small practice typically sit close to credentials, email, or document workflows — treat the patch as in-scope.
What to do
Apply updates per vendor instructions.
If you don't have someone in-house to verify the patch deployed across every endpoint — or you're not sure whether you're affected — that's exactly the kind of triage we do. Book a free 20-minute triage call.
Insurance readiness
Your insurer will ask if this is patched.
Unpatched entries on CISA's Known Exploited Vulnerabilities list are exactly what cyber-insurance carrier questionnaires probe for, and knowing which controls they check is how you keep a renewal from stalling.
Get the free carrier questionnaire →Severity
CVSS base score: 7.8 — HIGH
Microsoft fix
- KB4493474 (Security Update)
- KB4493464 (Security Update)
- KB4493509 (Security Update)
- KB4493441 (Security Update)
- KB4493475 (Security Update)
- KB4493470 (Security Update)
- KB4493472 (Monthly Rollup)
- KB4493448 (Security Only)
- KB4493446 (Monthly Rollup)
- KB4493467 (Security Only)
- KB4493471 (Monthly Rollup)
- KB4493458 (Security Only)
- KB4493451 (Monthly Rollup)
- KB4493450 (Security Only)
Microsoft Exploitability Index (assessed at update release): Exploitation More Likely
This CVE is on CISA's Known Exploited Vulnerabilities catalog. Microsoft's index reflects their release-time forecast, not current observed activity, and is not automatically revised upward when exploitation appears later.
Vendor workaround
No vendor workaround published. Patching is the only fix.
CISA due date
Federal deadline: May 3, 2022. Federal agencies must complete the required action by this date. For private SMBs the deadline is advisory — but treat it as a strong recommendation, especially if you handle regulated data (HIPAA, GLBA, ABA model rules).
EPSS
EPSS score: 4.2% — higher than 90% of all scored CVEs.
EPSS estimates the probability of exploitation activity in the next 30 days. Every entry on this site is already confirmed exploited, so read it as relative urgency among the things you still have open, not as permission to wait.
Other exploited Microsoft Win32k entries
More CISA KEV entries for Microsoft Win32k. Same product line, same actively-exploited status.
Source
This entry comes from CISA's Known Exploited Vulnerabilities catalog, public US-Government data we pull daily. The plain-language framing and the what-to-do guidance above are ours. View the original entry on cisa.gov.