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PatchSiren cyber security CVE debrief

CVE-2021-33742 Microsoft CVE debrief

CVE-2021-33742 is a Microsoft Windows MSHTML Platform remote code execution vulnerability that CISA added to its Known Exploited Vulnerabilities catalog. Because it is listed as known exploited, organizations should treat remediation as urgent and follow vendor update guidance without delay.

Vendor
Microsoft
Product
Windows
CVSS
HIGH 7.5
CISA KEV
Listed
Original CVE published
2021-11-03
Original CVE updated
2021-11-03
Advisory published
2021-11-03
Advisory updated
2021-11-03

Who should care

Windows administrators, endpoint security teams, and organizations that manage Microsoft Windows systems should prioritize this CVE. It is especially relevant for teams responsible for patching, vulnerability management, and exposure reduction on Windows endpoints and servers.

Technical summary

According to the supplied official records, CVE-2021-33742 is a Microsoft Windows MSHTML Platform remote code execution vulnerability. CISA marked it as a Known Exploited Vulnerability on 2021-11-03 and set a remediation due date of 2021-11-17, with the required action to apply updates per vendor instructions. The source corpus does not provide further technical detail beyond the vulnerability name and exploitation status.

Defensive priority

High. CISA inclusion in the Known Exploited Vulnerabilities catalog indicates confirmed exploitation and makes timely patching and exposure review a priority.

Recommended defensive actions

  • Apply Microsoft updates and follow vendor instructions as directed by CISA.
  • Prioritize affected Windows assets for immediate patching before non-critical maintenance work.
  • Verify whether any exposed or high-value Windows endpoints remain unpatched.
  • Use vulnerability management and endpoint telemetry to confirm remediation status across the fleet.
  • Monitor CISA and vendor advisories for any additional guidance related to this CVE.

Evidence notes

The supplied CISA KEV source identifies CVE-2021-33742 as "Microsoft Windows MSHTML Platform Remote Code Execution Vulnerability," with dateAdded 2021-11-03, dueDate 2021-11-17, requiredAction "Apply updates per vendor instructions," and knownRansomwareCampaignUse "Unknown." The source item also references the NVD detail page for the CVE. No CVSS score was provided in the supplied corpus.

Sources and references

Verified primary and authoritative sources

  • CVE-2021-33742 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2021-33742

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

  • CVE-2021-33742 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2021-33742

    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.