Skip to the content
The Update Bureau
Windows 10 1809 Windows 10 1809 Security update
Patch Tuesday Zero-day

KB5120238

KB5120238: Cumulative update for Windows 10, version 1809, August 2026. Exploited networking flaw; File History backups fixed

In short

Attackers are exploiting a Windows networking flaw to gain higher privileges. File History backups to SMB network shares also work again.

Does it affect you? Applies to: Devices running Windows 10 Enterprise LTSC 2019, version 1809.

Build
17763.9121
Security
162 fixed · 12 critical · 1 exploited
Restart
Required

Microsoft publishes separate notes for this KB for Windows Server.

What changes

Fix 1 change

Backup

  • File History automatic backups to SMB network shares copy files again instead of failing with an incorrect credentials error.1
    Resolves failures in File History automatic backups to network shares using Server Message Block (SMB); scheduled backups now copy files.

Improvement 1 change

Secure Boot

Gradual rollout Verified in package

For: PC users and IT administrators

  • More supported PCs become eligible to receive new Secure Boot certificates automatically over the coming months.2
    Adds high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released
2026-08-11
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaces
KB5099538, KB5094123, KB5087538, KB5091573
+21 earlier KB5082123, KB5078752, KB5075904, KB5078131, KB5077795, KB5073723, KB5074975, KB5071544, KB5068791, KB5066586, KB5065428, KB5066187, KB5063877, KB5062557, KB5060531, KB5061978, KB5058392, KB5059091, KB5058922, KB5050008, KB5037425
Replaced by
KB5122876
VersionBuildChannel
1809 17763.9121 General availability

Security

162 vulnerabilities fixed
1 exploited 12 critical 150 important
VulnerabilitySeverityCVSS
CVE-2026-68820 Exploited
Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability
 Important 7.0
CVE-2026-65791
Windows iSCSI Target Service Remote Code Execution Vulnerability
 Critical 9.8
CVE-2026-62816
Windows Reliable Multicast Transport Driver (RMCAST) Remote Code Execution Vulnerability
 Critical 8.8
CVE-2026-62818
Windows Active Directory Certificate Services (AD CS) Remote Code Execution Vulnerability
 Critical 8.8
CVE-2026-62822
Windows GDI+ Remote Code Execution Vulnerability
 Critical 8.8
CVE-2026-62819
Windows Routing and Remote Access Service (RRAS) Remote Code Execution Vulnerability
 Critical 8.1
CVE-2026-62889
Windows Secure Socket Tunneling Protocol (SSTP) Remote Code Execution Vulnerability
 Critical 8.1
CVE-2026-65679
Windows iSCSI Target Service Remote Code Execution Vulnerability
 Critical 8.1
CVE-2026-65796
Windows iSCSI Target Service Remote Code Execution Vulnerability
 Critical 8.1
CVE-2026-66802
Windows Device Health Attestation (DHA) Remote Code Execution Vulnerability
 Critical 8.1
CVE-2026-71331
Windows Device Health Attestation (DHA) Remote Code Execution Vulnerability
 Critical 8.1
CVE-2026-62890
Windows GDI+ Elevation of Privilege Vulnerability
 Critical 7.8
CVE-2026-66799
Windows Key Guard Elevation of Privilege Vulnerability
 Critical 7.8

The table lists the 13 exploited, publicly disclosed or critical vulnerabilities. See all 162 vulnerabilities →

Updated components

1,760 files changed since the previous update for the same versions.

Top changed componentsFiles
Remote Desktop29
Networking27
Security and sign-in27
Audio23
Graphics and display19
Bluetooth17
Secure Boot15
File Explorer and shell14
Hyper-V and virtualization12
Kernel10
Search9
Settings9

Verified in package: changed files confirm Secure Boot.

Page history

  1. Added 8 vulnerabilities (8 important)

  2. Removed CVE-2026-61346

    Removed CVE-2026-62740

    Removed CVE-2026-62752

    Removed CVE-2026-62800

    Removed CVE-2026-62877

    Removed CVE-2026-70344

Sources

Updated
Cited passages from Microsoft's official notes (2)
  1. 1. [Backup] File History automatic backups to network shares using Server Message Block (SMB) might fail with an incorrect "invalid credentials" error. When this issue occurs, scheduled backups do not copy any files. This update resolves the issue. support.microsoft.com
  2. 2. [Secure Boot] This update includes additional high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. support.microsoft.com
Checked automatically: 8 of 8 checks passed, 2 quoted passages · compared with Microsoft's page on Oct 20, 2026
  • Quotes found in the official pages: passed
  • Numbers found in the sources: passed
  • Vulnerabilities from the dossier only: passed
  • Links to allowed domains only: passed
  • Every official change covered: passed
  • Readable plain text: passed
  • Changes confirmed by the file list: passed
  • Sources agree: passed

A second AI read the text against the sources: correctness 5/5, clarity 4/5, completeness 5/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake