The Update BureauKB5120709: Cumulative update for .NET Framework, versions 3.5 and 4.8.1, on Windows 10 21H2/22H2, August 2026. Runtime vulnerabilities closed; WPF printing errors need later updates
Closes six .NET Framework vulnerabilities, including three remote-code-execution flaws. Two WPF printing issues are resolved only in later updates.
Does it affect you? Applies to: Devices running Windows 10, version 21H2 or 22H2, with .NET Framework 3.5 or 4.8.1 installed.
What changes
Fixes 6 changes
.NET Framework
For: Devices with .NET Framework 3.5 or 4.8.1 installed
-
Closes an elevation-of-privilege vulnerability, CVE-2026-65810.1
The vulnerability is in .NET Framework.
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Closes an elevation-of-privilege vulnerability, CVE-2026-62872.2
The vulnerability is in .NET Framework.
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Closes a remote-code-execution vulnerability, CVE-2026-62886.3
The vulnerability is in .NET Framework.
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Closes a remote-code-execution vulnerability, CVE-2026-62897.4
The vulnerability is in .NET Framework.
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Closes a remote-code-execution vulnerability, CVE-2026-70354.5
The vulnerability is in .NET Framework.
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Closes an information-disclosure vulnerability, CVE-2026-62902.6
The vulnerability is in .NET Framework.
Known issues
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After installing the August 2026 .NET Framework cumulative update, some WPF applications may fail with a System.IO.File…
Some WPF applications might fail with a System.IO.FileFormatException when printing or generating PDF/XPS content that uses certain fonts, including Calibri. The issue is resolved in the September 2026 .NET Framework cumulative update and later updates.7
How to apply the workaround WorkaroundAs a temporary measure, enable the AppContext switch in the application config file only when needed; this disables security protections introduced by the August update and might increase exposure to the vulnerabilities it addresses.7
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After installing the August 2026 .NET Framework cumulative update, WPF applications that print—or display print preview…
WPF applications might fail with a System.IO.FileFormatException when printing or displaying print preview for certain in-memory XPS documents that use a
pack-scheme package identity. The issue is resolved in the October 2026 .NET Framework cumulative update and later updates.8How to apply the workaround WorkaroundFor applications that can be rebuilt, use an absolute package identity without the
packscheme, such asxpspack://<guid>.xps. If an application cannot be rebuilt, enable the AppContext switch; this disables security protections introduced by the August update and might increase exposure to the vulnerabilities it addresses.8Step-by-step workaround instructionsShow steps Hide steps2 stepsStep-by-step procedure- If the application can be rebuilt, use an absolute package identity that does not use the
packscheme, such asxpspack://<guid>.xps. - If the application cannot be rebuilt, add
Switch.System.Windows.DisableXpsPackageBoundaryRestriction=trueto its configuration file.
- If the application can be rebuilt, use an absolute package identity that does not use the
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
- KB5101000, KB5087053
- Replaced by
- KB5126421
| Version | File version | Channel |
|---|---|---|
| 3.5 | 2.0.50727.9183 | General availability |
| 4.8.1 | 4.8.9343.0 | General availability |
Security
| Vulnerability | Severity | CVSS |
|---|---|---|
|
.NET Framework Elevation of Privilege Vulnerability
|
Important | 8.8 |
|
.NET Framework Elevation of Privilege Vulnerability
|
Important | 7.8 |
|
.NET Core Remote Code Execution Vulnerability
|
Important | 7.8 |
|
.NET Framework Remote Code Execution Vulnerability
|
Important | 7.0 |
|
.NET Elevation of Privilege Vulnerability
|
Not rated | — |
|
.NET Information Disclosure Vulnerability
|
Not rated | — |
Downloads (Microsoft Update Catalog)
Updated components
99 files changed since the previous update for the same versions.
| Top changed components | Files |
|---|---|
| WPF | 42 |
| ASP.NET | 18 |
| .NET runtime (CLR) | 6 |
Page history
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Added CVE-2026-62897 (Important)
Sources
Cited passages from Microsoft's official notes (8)
-
1.
This security update addresses an elevation of privilege vulnerability detailed in CVE-2026-65810.
support.microsoft.com -
2.
This security update addresses an elevation of privilege vulnerability detailed in CVE-2026-62872.
support.microsoft.com -
3.
This security update addresses a remote code execution vulnerability detailed in CVE-2026-62886.
support.microsoft.com -
4.
This security update addresses a remote code execution vulnerability detailed in CVE-2026-62897.
support.microsoft.com -
5.
This security update addresses a remote code execution vulnerability detailed in CVE-2026-70354.
support.microsoft.com -
6.
This security update addresses an information disclosure vulnerability detailed in CVE-2026-62902.
support.microsoft.com -
7.
This issue is resolved in the September 2026 .NET Framework cumulative update and later updates.
support.microsoft.com -
8.
This issue is resolved in the October 2026 .NET Framework cumulative update and later updates.
support.microsoft.com
Checked automatically: 7 of 8 checks passed, 8 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: not 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