Patch tracker / KB5120710
KB5120710: .NET Framework 3.5 and 4.8.1 Security Update (August 2026)
KB5120710 is a High security update for .NET Framework 3.5 and 4.8.1, released 2026-08-11. It closes 3 CVEs with a maximum CVSS of 8.8. Microsoft documents 1 known issue for this update, quoted below.
Before you deploy: Microsoft lists 1 known issue for this update.
Our data comes from Microsoft, CISA and other public sources, and it can be wrong or out of date. If you are unsure, check the linked source before you act, and tell us when we are wrong so we can fix it.
Update summary
Fixes 3 CVEs. Most severe CVSS 8.8 (High). EPSS exploit probability up to <1%. Among the lower half of tracked Microsoft updates by EPSS exploit probability.
Microsoft documents 1 known issue with this update.
- Known Issues: After installing the August 2026 .NET Framework cumulative update, some WPF applications may fail with a System.IO.FileFormatException...
Senserva AI Opinion and rich prompt for KB5120710
Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.
Full tracking and change history for KB5120710
- Released
- 2026-08-11
- Last changed
- 2026-09-26
- Changes tracked
- 3
Senserva began recording day-to-day change history on 2026-07-07, and refreshes it several times a day. Release dates are historical where Microsoft publishes them; revision history is tracked from that date forward, so it does not include changes made before then.
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Known issues, from Microsoft
Quoted from Microsoft's support article for KB5120710 (checked 2026-10-30). Microsoft lists 1 known issue. Verify against the article before acting.
Known Issues: After installing the August 2026 .NET Framework cumulative update, some WPF applications may fail with a System.IO.FileFormatException when printing or generating PDF/XPS content that uses certain fonts, including Calibri.
Workaround: Applications may mitigate the issue by enabling the Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection AppContext switch in the app config file, as shown below.
<configuration>
<runtime>
<AppContextSwitchOverrides
value="Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection=true"/>
</runtime>
</configuration>
This switch disables security protections introduced in the August 2026 update and may increase exposure to the vulnerabilities addressed by that update. Microsoft recommends using this workaround only as a temporary measure and only when required to address this issue.
Status: This issue is resolved in the September 2026 .NET Framework cumulative update and later updates. We recommend you install the latest update for your device as it contains important improvements and issue resolutions, including this one.
Known Issues: After installing the August 2026 .NET Framework cumulative update, WPF applications that print—or display print preview—from an in-memory XPS document registered with System.IO.Packaging.PackageStore may fail with a System.IO.FileFormatException while the document is loading. This occurs when the package identity used as both the PackageStore key and the XpsDocument package identity is an absolute URI that uses the pack scheme—for example, pack://<guid>.xps . Images and fonts contained within the same XPS package are then incorrectly rejected as being outside the package. Application code and XPS content do not need to have changed for this failure to occur.
Workaround: Applications that can be rebuilt should use an absolute package identity that does not use the pack scheme—for example, xpspack://<guid>.xps . This resolves the failure while keeping the protections introduced in the August 2026 update enabled. For applications that cannot be rebuilt, enable the Switch.System.Windows.DisableXpsPackageBoundaryRestriction AppContext switch in the application configuration file:
<configuration>
<runtime>
<AppContextSwitchOverrides
value="Switch.System.Windows.DisableXpsPackageBoundaryRestriction=true"/>
</runtime>
</configuration>
This switch disables security protections introduced in the August 2026 update and may increase exposure to the vulnerabilities addressed by that update. Microsoft recommends using this workaround only as a temporary measure and only when required to address this issue.
Status: This issue is resolved in the October 2026 .NET Framework cumulative update and later updates. We recommend you install the latest update for your device as it contains important improvements and issue resolutions, including this one.
CVEs fixed by this update
Sorted exploited-first, then by CVSS. Every CVE links to its Senserva page with the full risk facts, references, and a ready-to-paste AI prompt.
| CVE | Severity | CVSS | EPSS | Exploited |
|---|---|---|---|---|
| CVE-2026-62872 | High | 8.8 | <1% | No |
| CVE-2026-65810 | High | 7.8 | <1% | No |
| CVE-2026-70354 | High | 7.8 | <1% | No |
Scope and sources
- Affected products
- Also released in August 2026
KB5120228
204 CVEs · Critical · exploitedKB5120229
184 CVEs · Critical · exploitedKB5120233
204 CVEs · Critical · exploitedKB5120238
174 CVEs · Critical · exploitedKB5120240
160 CVEs · Critical · exploitedKB5120242
184 CVEs · Critical · exploitedKB5120385
136 CVEs · Critical · exploitedKB5120386
131 CVEs · Critical · exploitedThe full month, summarized: Microsoft Patch Tuesday.
- Authoritative references
See this and every Microsoft update ranked by real-world risk on the Microsoft Patch Tracker.