IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2023-29336|Auth: low — authenticated user|Reboot: required|Manual only

KB5026363: Windows Server 2016 / 2012 R2 Security Update (May 2023)

Microsoft Win32k contains an unspecified vulnerability that allows for privilege escalation up to SYSTEM privileges.

Published May 9, 2023 · Updated Jun 10, 2026
XLinkedIn
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 2023-05-30 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Use After Free (CWE-416) vulnerability in Microsoft Win32k. 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 1507: v < 10.0.10240.19926; windows 10 1607: v < 10.0.14393.5921; windows server 2008: -, r2; windows server 2012: -, r2; windows server 2016: -

Affected OS versions

Windows Server 2016Windows Server 2012 R2
Fixed inKB5026363, KB5026382, KB5026408, KB5026409, KB5026411, KB5026413, KB5026415, KB5026419, KB5026426, KB5026427 (applies to 16 product versions) — build 10.0.10240.19926, 10.0.14393.5921+
Real-world incidentsWhat we've seen

Active exploitation documented in the wild. Threat-research write-up: https://www.exploit-db.com/exploits/52301

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 CatalogKB5026363

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB5026363 — https://support.microsoft.com/help/5026363
    1
    KB5026382 — https://support.microsoft.com/help/5026382
    1
    KB5026408 — https://support.microsoft.com/help/5026408
    1
    KB5026409 — https://support.microsoft.com/help/5026409
    1
    KB5026411 — https://support.microsoft.com/help/5026411
    1
    KB5026413 — https://support.microsoft.com/help/5026413
    1
    KB5026415 — https://support.microsoft.com/help/5026415
    1
    KB5026419 — https://support.microsoft.com/help/5026419
    1
    KB5026426 — https://support.microsoft.com/help/5026426
    1
    KB5026427 — https://support.microsoft.com/help/5026427

Supersedes: KB5025228, KB5025234, KB5025271, KB5025279, KB5025285, KB5025287

Affected Products

    1
    Windows 10 Version 1607 for 32-bit Systems
    1
    Windows 10 Version 1607 for x64-based Systems
    1
    Windows 10 for 32-bit Systems
    1
    Windows 10 for x64-based Systems
    1
    Windows Server 2008 R2 for x64-based Systems Service Pack 1
    1
    Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation)
    1
    Windows Server 2008 for 32-bit Systems Service Pack 2
    1
    Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation)
    1
    Windows Server 2008 for x64-based Systems Service Pack 2
    1
    Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation)
    1
    Windows Server 2012
    1
    Windows Server 2012 (Server Core installation)
    1
    Windows Server 2012 R2
    1
    Windows Server 2012 R2 (Server Core installation)
    1
    Windows Server 2016
    1
    Windows Server 2016 (Server Core installation)

Fixed Build Numbers

    1
    10.0.10240.19926
    1
    10.0.14393.5921
    1
    6.0.6003.22070
    1
    6.1.7601.26519
    1
    6.2.9200.24266
    1
    6.3.9600.20969

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 KB5026363
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 KB5026363 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5026363
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5026382
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5026408
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5026409
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5026411
    1
    (…5 more)

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5026363','KB5026382','KB5026408','KB5026409','KB5026411','KB5026413','KB5026415','KB5026419','KB5026426','KB5026427') }

References

    1
    Microsoft Security Response Center: https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2023-29336
    1
    KB article: https://support.microsoft.com/help/5026363
    1
    KB article: https://support.microsoft.com/help/5026382
    1
    KB article: https://support.microsoft.com/help/5026408
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2023-29336
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-29336

Discovery Credit

Jan Vojtěšek, Milánek, and Luigino Camastra with Avast

PowerShell automationComing soon

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

References

↗ CVE-2023-29336↗ MSRC Advisory↗ KBKB5026363

Related vulnerabilities

CRITICAL9.8

KB5000871: Windows Server 2016 / 2019 Security Update (May 2026)

Microsoft Exchange Server

CVE-2021-26855

MEDIUM6.5

Microsoft Defender for Identity Improper Authentication — Spoofing (CVE-2025-26685)

Microsoft Defender for Identity

CVE-2025-26685

HIGH

IIS Security Updates Require Both Windows Update and Manual Configuration Review

Microsoft IIS