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PatchSiren cyber security CVE debrief

CVE-2021-31955 Microsoft CVE debrief

CVE-2021-31955 is a Microsoft Windows Kernel information disclosure vulnerability that CISA added to the Known Exploited Vulnerabilities catalog on 2021-11-03. Because CISA marked it as known exploited and set a remediation due date of 2021-11-17, defenders should treat it as a high-priority patching item for Windows environments.

Vendor
Microsoft
Product
Windows
CVSS
MEDIUM 5.5
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 and security operations teams, vulnerability management staff, and incident responders should care most about this issue, especially anyone responsible for tracking CISA KEV items across managed Windows systems.

Technical summary

The supplied corpus identifies CVE-2021-31955 as a Microsoft Windows Kernel information disclosure vulnerability. The CISA KEV entry confirms it as a known exploited vulnerability and instructs organizations to apply updates per vendor instructions. The corpus does not provide CVSS scoring or deeper technical details about the disclosure mechanism.

Defensive priority

Urgent

Recommended defensive actions

  • Apply the relevant Microsoft updates for Windows as soon as possible.
  • Confirm whether any affected Windows systems are still unpatched and prioritize them ahead of non-KEV issues.
  • Track remediation against CISA’s due date of 2021-11-17 for this KEV entry.
  • Validate patch deployment across endpoints, servers, and any centralized Windows management rings.
  • Use the CISA KEV and NVD entries as references in your remediation tracking and reporting.

Evidence notes

The CISA Known Exploited Vulnerabilities source item lists vendorProject Microsoft, product Windows, vulnerabilityName Microsoft Windows Kernel Information Disclosure Vulnerability, dateAdded 2021-11-03, dueDate 2021-11-17, and requiredAction 'Apply updates per vendor instructions.' The source item also references the NVD detail page for CVE-2021-31955. The CVE and official record links corroborate the vulnerability identity and publication timing.

Sources and references

Verified primary and authoritative sources

  • CVE-2021-31955 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2021-31955

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

  • CVE-2021-31955 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2021-31955

    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.