IRONSMITHINTEL
HIGHCVSS7.8
|
Actively Exploited
|CISA KEV|CVE-2025-24990|Auth: low — authenticated user|Reboot: required|Manual only

KB5066586: Windows Server Security Update (October 2025)

Microsoft Windows Agere Modem Driver contains an untrusted pointer dereference vulnerability that allows for privilege escalation. An attacker who successfully exploited this vulnerability could gain administrator privileges.

Published Oct 14, 2025 · 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 2025-11-04 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Software Vulnerability (CWE-822) (CWE-822) vulnerability in Microsoft Windows. Microsoft is aware of vulnerabilities in the third party Agere Modem driver that ships natively with supported Windows operating systems. This is an announcement of the upcoming removal of ltmdm64.sys driver. The driver has been removed in the October cumulative update. Fax modem hardware dependent on this specific driver will no longer work on Windows. Microsoft recommends removing any existing dependencies on this hardware. 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:

●Windows Administrators
●Systems Engineers
●IT Security
●Running windows 10 1507: v < 10.0.10240.21161; windows 10 1607: v < 10.0.14393.8519; windows 10 1809: v < 10.0.17763.7919; windows 10 21h2: v < 10.0.19044.6456; windows 10 22h2: v < 10.0.19045.6456; windows 11 22h2: v < 10.0.22621.6060; windows 11 23h2: v ≤ 10.0.22631.6060; windows 11 24h2: v < 10.0.26100.6899; windows 11 25h2: v < 10.0.26200.6899; windows server 2008: -, r2; windows server 2012: -, r2; windows server 2016: v ≤ 10.0.14393.8519; windows server 2019: v < 10.0.17763.7919; windows server 2022: v < 10.0.20348.4294; windows server 2022 23h2: v < 10.0.25398.1913; windows server 2025: v ≤ 10.0.26100.6899
Fixed inKB5066586, KB5066780, KB5066782, KB5066791, KB5066793, KB5066835, KB5066836, KB5066837, KB5066872, KB5066873, KB5066874, KB5066875, KB5066876, KB5066877 (applies to 26 product versions) — build 10.0.10240.21161, 10.0.14393.8519+
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2025-10-14 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2025-11-04.

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 CatalogKB5066586

Manual remediation steps

Apply the Microsoft Security Update

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

Required KB Updates

    1
    KB5066586 — https://support.microsoft.com/help/5066586
    1
    KB5066780 — https://support.microsoft.com/help/5066780
    1
    KB5066782 — https://support.microsoft.com/help/5066782
    1
    KB5066791 — https://support.microsoft.com/help/5066791
    1
    KB5066793 — https://support.microsoft.com/help/5066793
    1
    KB5066835 — https://support.microsoft.com/help/5066835
    1
    KB5066836 — https://support.microsoft.com/help/5066836
    1
    KB5066837 — https://support.microsoft.com/help/5066837
    1
    KB5066872 — https://support.microsoft.com/help/5066872
    1
    KB5066873 — https://support.microsoft.com/help/5066873
    1
    KB5066874 — https://support.microsoft.com/help/5066874
    1
    KB5066875 — https://support.microsoft.com/help/5066875
    1
    KB5066876 — https://support.microsoft.com/help/5066876
    1
    KB5066877 — https://support.microsoft.com/help/5066877

Supersedes: KB5065425, KB5065426, KB5065427, KB5065428, KB5065429, KB5065430, KB5065431, KB5065432, KB5065468, KB5065507, KB5065508, KB5065509

Affected Products

    1
    Windows 10 Version 1607 for x64-based Systems
    1
    Windows 10 Version 1809 for x64-based Systems
    1
    Windows 10 Version 21H2 for x64-based Systems
    1
    Windows 10 Version 22H2 for x64-based Systems
    1
    Windows 10 for x64-based Systems
    1
    Windows 11 Version 22H2 for x64-based Systems
    1
    Windows 11 Version 23H2 for x64-based Systems
    1
    Windows 11 Version 24H2 for x64-based Systems
    1
    Windows 11 Version 25H2 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 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)
    1
    Windows Server 2019
    1
    (…6 more product versions)

Fixed Build Numbers

    1
    10.0.10240.21161
    1
    10.0.14393.8519
    1
    10.0.17763.7919
    1
    10.0.19044.6456
    1
    10.0.19045.6456
    1
    10.0.20348.4294
    1
    10.0.22621.6060
    1
    10.0.22631.6060
    1
    10.0.25398.1913
    1
    10.0.26100.6899
    1
    (…5 more builds)

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 KB5066586
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 KB5066586 for the affected products in your update management console.

Microsoft Download Center Links

    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5066586
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5066780
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5066782
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5066791
    1
    https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB5066793
    1
    (…9 more)

Verification

Confirm the update is installed:

Get-HotFix | Where-Object { $_.HotFixID -in @('KB5066586','KB5066780','KB5066782','KB5066791','KB5066793','KB5066835','KB5066836','KB5066837','KB5066872','KB5066873','KB5066874','KB5066875','KB5066876','KB5066877') }

References

    1
    Microsoft Security Response Center: https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2025-24990
    1
    KB article: https://support.microsoft.com/help/5066586
    1
    KB article: https://support.microsoft.com/help/5066780
    1
    KB article: https://support.microsoft.com/help/5066782
    1
    NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2025-24990
    1
    CISA KEV: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-24990

Discovery Credit

Fabian Mosch with r-tec IT Security GmbH Jordan Jay, Anonymous, MSTIC

PowerShell automationComing soon

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

References

↗ CVE-2025-24990↗ MSRC Advisory↗ NVD↗ KBKB5066586