Skip to the content
The Update Bureau
.NET Framework 3.5 / 4.8.1 .NET Framework 3.5 / 4.8.1 Security update
Patch Tuesday

KB5127691

KB5127691: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows 11 26H1, October 2026. Critical AD FS spoofing flaw and public .NET bypass fixed

In short

Fixes 20 security flaws, including a Critical AD FS spoofing flaw and a publicly disclosed .NET Framework flaw that bypasses a security feature. Restart if affected files are in use.

Does it affect you? Applies to: Devices running Windows 11, version 26H1, with .NET Framework 4.8.1 installed.

File version
4.8.9363.0
Security
20 fixed · 1 critical
Restart
Required
Review notes Additional details from the official release notes (1) Read note
  • What changes CVE-2026-102869 is also recorded as an Important vulnerability added for this update.

The official sources are linked at the end of the page.

What changes

Fixes 19 changes

.NET Framework

19 items
  • A .NET Framework flaw that could cause a denial of service is fixed.1
    CVE-2026-58280 — Denial of Service.
  • A .NET Framework flaw that could let someone gain higher access is fixed.2
    CVE-2026-69439 — Elevation of Privilege.
  • A .NET Framework flaw that could cause a denial of service is fixed.3
    CVE-2026-69651 — Denial of Service.
  • A .NET Framework flaw that could let an attacker run code remotely is fixed.4
    CVE-2026-70007 — Remote Code Execution.
  • A .NET Framework flaw that could let an attacker run code remotely is fixed.5
    CVE-2026-70035 — Remote Code Execution.
  • A .NET Framework flaw that could let an attacker run code remotely is fixed.6
    CVE-2026-70174 — Remote Code Execution.
  • A .NET Framework flaw that could let an attacker run code remotely is fixed.7
    CVE-2026-83520 — Remote Code Execution.
  • A .NET Framework flaw that could cause a denial of service is fixed.8
    CVE-2026-84008 — Denial of Service.
  • A .NET Framework flaw that could let someone gain higher access is fixed.9
    CVE-2026-85363 — Elevation of Privilege.
  • A .NET Framework flaw that could let an attacker run code remotely is fixed.10
    CVE-2026-87697 — Remote Code Execution.
  • A .NET Framework spoofing flaw is fixed.11
    CVE-2026-96222 — Spoofing.
  • A .NET Framework flaw that could let an attacker run code remotely is fixed.12
    CVE-2026-96224 — Remote Code Execution.
  • A .NET Framework flaw that could cause a denial of service is fixed.13
    CVE-2026-96233 — Denial of Service.
  • A .NET Framework flaw that could cause a denial of service is fixed.14
    CVE-2026-96958 — Denial of Service.
  • A .NET Framework flaw that could cause a denial of service is fixed.15
    CVE-2026-96959 — Denial of Service.
  • A .NET Framework flaw that could cause a denial of service is fixed.16
    CVE-2026-96960 — Denial of Service.
  • A .NET Framework flaw that could reveal information is fixed.17
    CVE-2026-97788 — Information Disclosure.
  • A .NET Framework flaw that could let someone tamper with data is fixed.18
    CVE-2026-97801 — Tampering.
  • A .NET Framework flaw that could bypass a security feature is fixed.19
    CVE-2026-108398 — Security Feature Bypass.

Technical details

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

Data sheet

Released
2026-10-13
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaces
KB5126053, KB5122386, KB5120711, KB5101002
+4 earlier KB5092431, KB5087055, KB5082421, KB5074837
VersionFile versionChannel
3.5 General availability
4.8.1 4.8.9363.0 General availability

Security

20 vulnerabilities fixed
1 critical 17 important 2 not rated
VulnerabilitySeverityCVSS
CVE-2026-96222
Active Directory Federation Services (AD FS) Spoofing Vulnerability
 Critical 7.4
CVE-2026-102869
.NET and Visual Studio Elevation of Privilege Vulnerability
 Important 8.8
CVE-2026-108398
.NET Framework Security Feature Bypass Vulnerability
 Important 8.8
CVE-2026-70007
.NET Framework Remote Code Execution Vulnerability
 Important 8.8
CVE-2026-70035
.NET Framework Remote Code Execution Vulnerability
 Important 8.8
CVE-2026-70174
.NET Remote Code Execution Vulnerability
 Important 8.8
CVE-2026-83520
.NET Remote Code Execution Vulnerability
 Important 8.8
CVE-2026-85363
.NET Framework Elevation of Privilege Vulnerability
 Important 8.8
CVE-2026-96224
.NET Remote Code Execution Vulnerability
 Important 8.8
CVE-2026-58280
.NET Denial of Service Vulnerability
 Important 7.5
CVE-2026-69651
.NET Denial of Service Vulnerability
 Important 7.5
CVE-2026-84008
.NET Denial of Service Vulnerability
 Important 7.5
CVE-2026-96233
ASP.NET Core Denial of Service Vulnerability
 Important 7.5
CVE-2026-96958
.NET Denial of Service Vulnerability
 Important 7.5
CVE-2026-96959
.NET Denial of Service Vulnerability
 Important 7.5
CVE-2026-96960
.NET Denial of Service Vulnerability
 Important 7.5
CVE-2026-97788
Active Directory Federation Services (AD FS) Information Disclosure Vulnerability
 Important 7.5
CVE-2026-97801
.NET Framework Tampering Vulnerability
 Important 7.5
CVE-2026-69439
.NET and Visual Studio Elevation of Privilege Vulnerability
 Not rated —
CVE-2026-87697
.NET Remote Code Execution Vulnerability
 Not rated —

Downloads (Microsoft Update Catalog)

Arm64 Windows 11, version 26H1
59.0 MB
windows11.0-kb5127691-arm64-ndp481.msu Main update · KB5127691 SHA-1: 0ca71446…a5f324

Updated components

103 files changed since the previous update for the same versions.

Top changed componentsFiles
WPF24
.NET runtime (CLR)14
WCF12
.NET data access2

Sources

Updated
Cited passages from Microsoft's official notes (19)
  1. 1. This security update addresses a denial of service vulnerability detailed in CVE-2026-58280. support.microsoft.com
  2. 2. This security update addresses an elevation of privilege vulnerability detailed in CVE-2026-69439. support.microsoft.com
  3. 3. This security update addresses a denial of service vulnerability detailed in CVE-2026-69651. support.microsoft.com
  4. 4. This security update addresses a remote code execution vulnerability detailed in CVE-2026-70007. support.microsoft.com
  5. 5. This security update addresses a remote code execution vulnerability detailed in CVE-2026-70035. support.microsoft.com
  6. 6. This security update addresses a remote code execution vulnerability detailed in CVE-2026-70174. support.microsoft.com
  7. 7. This security update addresses a remote code execution vulnerability detailed in CVE-2026-83520. support.microsoft.com
  8. 8. This security update addresses a denial of service vulnerability detailed in CVE-2026-84008. support.microsoft.com
  9. 9. This security update addresses an elevation of privilege vulnerability detailed in CVE-2026-85363. support.microsoft.com
  10. 10. This security update addresses a remote code execution vulnerability detailed in CVE-2026-87697. support.microsoft.com
  11. 11. This security update addresses a spoofing vulnerability detailed in CVE-2026-96222. support.microsoft.com
  12. 12. This security update addresses a remote code execution vulnerability detailed in CVE-2026-96224. support.microsoft.com
  13. 13. This security update addresses a denial of service vulnerability detailed in CVE-2026-96233. support.microsoft.com
  14. 14. This security update addresses a denial of service vulnerability detailed in CVE-2026-96958. support.microsoft.com
  15. 15. This security update addresses a denial of service vulnerability detailed in CVE-2026-96959. support.microsoft.com
  16. 16. This security update addresses a denial of service vulnerability detailed in CVE-2026-96960. support.microsoft.com
  17. 17. This security update addresses an information disclosure vulnerability detailed in CVE-2026-97788. support.microsoft.com
  18. 18. This security update addresses a tampering vulnerability detailed in CVE-2026-97801. support.microsoft.com
  19. 19. This security update addresses a security feature bypass vulnerability detailed in CVE-2026-108398. support.microsoft.com
Checked automatically: 7 of 8 checks passed, 19 quoted passages · compared with Microsoft's page on Nov 14, 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: not passed

A second AI read the text against the sources: correctness 4/5, clarity 5/5, completeness 3/5. 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