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PatchSiren cyber security CVE debrief

CVE-2021-40450 Microsoft CVE debrief

CVE-2021-40450 is a Microsoft Win32k privilege escalation vulnerability that CISA added to the Known Exploited Vulnerabilities (KEV) catalog on 2022-04-25. Because CISA identified it as known exploited, this should be treated as a high-priority patch item for Windows environments. Remediation should follow Microsoft’s update guidance and CISA’s required action to apply updates per vendor instructions.

Vendor
Microsoft
Product
Win32k
CVSS
HIGH 7.8
CISA KEV
Listed
Original CVE published
2022-04-25
Original CVE updated
2022-04-25
Advisory published
2022-04-25
Advisory updated
2022-04-25

Who should care

Windows administrators, endpoint security teams, SOC analysts, and IT operations teams responsible for Microsoft-managed fleets should prioritize this issue. Any organization with Windows systems should verify that the applicable Microsoft fixes have been deployed and documented.

Technical summary

CVE-2021-40450 is a Microsoft Win32k privilege escalation issue. The available official sources in this corpus do not provide detailed attack mechanics, but CISA’s KEV listing confirms known exploitation and elevates the operational urgency. The practical defensive takeaway is to patch affected Windows systems using Microsoft’s guidance and confirm the remediation across the environment.

Defensive priority

High. CISA placed this CVE in the KEV catalog, and the catalog entry sets a remediation due date of 2022-05-16. Treat it as an urgent patch-and-verify item for Windows assets.

Recommended defensive actions

  • Apply Microsoft updates and follow the vendor instructions referenced by CISA.
  • Verify that all eligible Windows systems in the fleet received the fix, including remote and rarely used endpoints.
  • Track and remediate any exceptions quickly; if immediate patching is not possible, apply temporary compensating controls until updates are installed.
  • Monitor endpoints for suspicious privilege-escalation behavior and post-exploitation activity while remediation is in progress.
  • Confirm remediation status against the KEV due date and document closure for audit and risk tracking.

Evidence notes

The CVE and product naming come from the official CVE record and NVD entry. CISA’s KEV feed entry and catalog indicate the vulnerability is known exploited, with dateAdded 2022-04-25 and dueDate 2022-05-16. The source corpus does not include a CVSS score or detailed technical exploitation notes, so this debrief stays limited to the official public records provided.

Sources and references

Verified primary and authoritative sources

  • CVE-2021-40450 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2021-40450

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2021-40450 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2021-40450

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

  • CISA Known Exploited Vulnerabilities catalog

    Publisher, destination, and source semantics verified

    URL: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

    Cybersecurity and Infrastructure Security Agency - Official CISA catalog of vulnerabilities known to be exploited in the wild.

Supplemental references

  • Source item URL

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

    cisa_kev

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.