IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2021-1647|Auth: low — authenticated user|Reboot: required|Manual only

Microsoft Defender Remote Code Execution Vulnerability

Microsoft Defender contains an unspecified vulnerability that allows for remote code execution.

Published Jan 12, 2021 · Updated May 16, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A local attacker, with a low-privilege account, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2021-11-17 under CISA BOD 22-01.

How the attack worksNo clicks needed

This vulnerability affects Microsoft Defender. Exploitation requires local access, low attack complexity, a low-privilege authenticated account, and no user interaction required.

Am I affected?Quick check

Probably yes if any of these apply:

●IT Security
●Running windows defender: -; security essentials: -; system center endpoint protection: -, 2012
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2021-11-03 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2021-11-17.

How to patch

Manual remediation steps

Apply the Vendor Patch

This vulnerability is in the CISA Known Exploited Vulnerabilities catalog — apply the vendor's security update as soon as possible.

CISA required action: Apply updates per vendor instructions.

References

    1
    Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-1647
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-1647
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-1647
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References

↗ CVE-2021-1647↗ MSRC Advisory↗ NVD