IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2021-1732|Auth: low — authenticated user|Reboot: required|Manual only

KB4601315: Windows Server Security Update (February 2021)

Microsoft Win32k contains an unspecified vulnerability that allows for privilege escalation.

Published Feb 25, 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. CISA has confirmed use of this vulnerability in known ransomware campaigns — treat as high priority for remediation. Federal agencies are required to remediate by 2021-11-17 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Out-of-bounds Write (CWE-787) vulnerability in Microsoft Win32k. Windows Win32k Elevation of Privilege Vulnerability 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 10 1803: -; windows 10 1809: -; windows 10 1909: -; windows 10 2004: -; windows 10 20h2: -; windows server 1909: -; windows server 2004: -; windows server 2019: -; windows server 20h2: -
Fixed inKB4601315, KB4601319, KB4601345, KB4601354 (applies to 19 product versions)
Real-world incidentsWhat we've seen

Used in known ransomware campaigns. Threat-research write-up: http://packetstormsecurity.com/files/161880/Win32k-ConsoleControl-Offset-Confusion.html

How to patch

Manual download

For air-gapped servers or out-of-band deployment. Microsoft Update Catalog returns every OS-version variant of this update.

↗ Microsoft Update CatalogKB4601315

Manual remediation steps

Apply the Microsoft Security Update

Microsoft has released an official security update that fixes this vulnerability.

Required KB Updates

    1
    KB4601315 — https://support.microsoft.com/help/4601315
    1
    KB4601319 — https://support.microsoft.com/help/4601319
    1
    KB4601345 — https://support.microsoft.com/help/4601345
    1
    KB4601354 — https://support.microsoft.com/help/4601354

Supersedes: KB4598229, KB4598230, KB4598242, KB4598245

Affected Products

    1
    Windows 10 Version 1803 for 32-bit Systems
    1
    Windows 10 Version 1803 for ARM64-based Systems
    1
    Windows 10 Version 1803 for x64-based Systems
    1
    Windows 10 Version 1809 for 32-bit Systems
    1
    Windows 10 Version 1809 for ARM64-based Systems
    1
    Windows 10 Version 1809 for x64-based Systems
    1
    Windows 10 Version 1909 for 32-bit Systems
    1
    Windows 10 Version 1909 for ARM64-based Systems
    1
    Windows 10 Version 1909 for x64-based Systems
    1
    Windows 10 Version 2004 for 32-bit Systems
    1
    Windows 10 Version 2004 for ARM64-based Systems
    1
    Windows 10 Version 2004 for x64-based Systems
    1
    Windows 10 Version 20H2 for 32-bit Systems
    1
    Windows 10 Version 20H2 for ARM64-based Systems
    1
    Windows Server 2019
    1
    Windows Server 2019 (Server Core installation)
    1
    Windows Server, version 1909 (Server Core installation)
    1
    Windows Server, version 2004 (Server Core installation)
    1
    Windows Server, version 20H2 (Server Core Installation)

Installation Methods

Windows Update (recommended)

1
Settings → Windows Update → Check for updates
2
The security update is offered if your system is in scope
3
Restart when prompted — a reboot IS required to complete the install

Microsoft Update Catalog (manual download)

1
Open https://catalog.update.microsoft.com
2
Search for KB4601315
3
Download the package matching your OS architecture and Windows build
4
Run the .msu installer with administrator privileges
5
Restart when prompted

WSUS / SCCM / Intune

Approve KB4601315 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4601315
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4601319
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4601345
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4601354

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB4601315','KB4601319','KB4601345','KB4601354') }

References

    1
    Microsoft Security Response Center: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-1732
    1
    KB article: https://support.microsoft.com/help/4601315
    1
    KB article: https://support.microsoft.com/help/4601319
    1
    KB article: https://support.microsoft.com/help/4601345
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-1732
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-1732

Discovery Credit

YanZiShuang(@madongze) of Big CJTeam and Gcow Team, JinQuan, MaDongZe, TuXiaoYi, and LiHao of DBAPPSecurity Co., Ltd

PowerShell automationComing soon

No tested PowerShell script for this entry yet. We’re prioritising automation based on user demand.

References

↗ CVE-2021-1732↗ MSRC Advisory↗ NVD↗ KBKB4601315