From 05c375ad8108709a2d65a7374c742e3a820f0788 Mon Sep 17 00:00:00 2001 From: Tara Overfield Date: Wed, 2 Sep 2026 08:40:15 -0700 Subject: [PATCH 1/7] Update 08-11-august-cumulative-update.md --- .../2026/08-11-august-cumulative-update.md | 49 ++++++++++++++++++- 1 file changed, 47 insertions(+), 2 deletions(-) diff --git a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md index 1f7f25c3b7023..9925037627ab4 100644 --- a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md +++ b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md @@ -1,12 +1,13 @@ --- title: August 2026 cumulative update description: Learn about the improvements in the .NET Framework August 2026 cumulative update. -ms.date: 08/11/2026 +ms.date: 09/02/2026 ai-usage: ai-generated --- # .NET Framework August 2026 cumulative update _Released August 11, 2026_ +_Updated Septemner 2, 2026 to include known issues_ ## Summary of what's new in this release @@ -45,7 +46,51 @@ There are no new quality and reliability improvements in this release. ## Known issues in this release -This release contains no known issues. +#### Known Issue + +After installing the August 2026 .NET Framework cumulative update, some Windows Presentation Foundation (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 this issue by enabling the `Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection` AppContext switch in the application configuration file: + +```xml + + + + + +``` + +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 + +Investigating. + +#### Known Issue + +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://.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://.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: + +```xml + + + + + +``` + +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 + +Investigating. ## Summary tables From ed67a54b4a4aa8409b62ccda961ce1b76c2535f2 Mon Sep 17 00:00:00 2001 From: Tara Overfield Date: Wed, 2 Sep 2026 12:48:05 -0700 Subject: [PATCH 2/7] Fix typo in release notes date update Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com> --- .../release-notes/2026/08-11-august-cumulative-update.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md index 9925037627ab4..2b0d34d59bd92 100644 --- a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md +++ b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md @@ -7,7 +7,7 @@ ai-usage: ai-generated # .NET Framework August 2026 cumulative update _Released August 11, 2026_ -_Updated Septemner 2, 2026 to include known issues_ +_Updated September 2, 2026, to include known issues._ ## Summary of what's new in this release From 922f91622730808fe585e381edafa83814bde967 Mon Sep 17 00:00:00 2001 From: Tara Overfield Date: Wed, 2 Sep 2026 12:48:25 -0700 Subject: [PATCH 3/7] Clarify known issues and workarounds in release notes Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com> --- .../release-notes/2026/08-11-august-cumulative-update.md | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md index 2b0d34d59bd92..22134ba1ed49b 100644 --- a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md +++ b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md @@ -48,11 +48,11 @@ There are no new quality and reliability improvements in this release. #### Known Issue -After installing the August 2026 .NET Framework cumulative update, some Windows Presentation Foundation (WPF) applications may fail with a `System.IO.FileFormatException` when printing or generating PDF/XPS content that uses certain fonts, including Calibri. +After installing the August 2026 .NET Framework cumulative update, some Windows Presentation Foundation (WPF) applications might fail with a `System.IO.FileFormatException` when printing or generating PDF/XPS content that uses certain fonts, including Calibri. #### Workaround -Applications may mitigate this issue by enabling the `Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection` AppContext switch in the application configuration file: +Applications can mitigate this issue by enabling the `Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection` AppContext switch in the application configuration file: ```xml From c1babc3206c440b1a5ae49a74aa2889e16d256c3 Mon Sep 17 00:00:00 2001 From: Tara Overfield Date: Wed, 2 Sep 2026 12:49:00 -0700 Subject: [PATCH 4/7] Update docs/framework/release-notes/2026/08-11-august-cumulative-update.md Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com> --- .../release-notes/2026/08-11-august-cumulative-update.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md index 22134ba1ed49b..8dc7707416a4e 100644 --- a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md +++ b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md @@ -63,7 +63,7 @@ value="Switch.MS.Internal.TtfDelta.DisableCmapAndSbitOverflowProtection=true"/> ``` -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. +This switch disables security protections introduced in the August 2026 update and might 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 From 3a62912072dcb157f3407d22d9284d7c8c75100a Mon Sep 17 00:00:00 2001 From: Tara Overfield Date: Wed, 2 Sep 2026 12:49:11 -0700 Subject: [PATCH 5/7] Update docs/framework/release-notes/2026/08-11-august-cumulative-update.md Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com> --- .../release-notes/2026/08-11-august-cumulative-update.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md index 8dc7707416a4e..ded61d052b196 100644 --- a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md +++ b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md @@ -75,7 +75,7 @@ After installing the August 2026 .NET Framework cumulative update, WPF applicati #### Workaround -Applications that can be rebuilt should use an absolute package identity that does not use the `pack` scheme—for example, `xpspack://.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: +Applications that can be rebuilt should use an absolute package identity that doesn't use the `pack` scheme—for example, `xpspack://.xps`. This resolves the failure while keeping the protections introduced in the August 2026 update enabled. For applications that can't be rebuilt, enable the `Switch.System.Windows.DisableXpsPackageBoundaryRestriction` AppContext switch in the application configuration file: ```xml From 178303301851086d6ac483b21fce2f2e4642e3d8 Mon Sep 17 00:00:00 2001 From: Tara Overfield Date: Wed, 2 Sep 2026 12:49:22 -0700 Subject: [PATCH 6/7] Update docs/framework/release-notes/2026/08-11-august-cumulative-update.md Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com> --- .../release-notes/2026/08-11-august-cumulative-update.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md index ded61d052b196..5017d53121456 100644 --- a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md +++ b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md @@ -86,7 +86,7 @@ value="Switch.System.Windows.DisableXpsPackageBoundaryRestriction=true"/> ``` -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. +This switch disables security protections introduced in the August 2026 update and might 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 From c200af6eedcb5bd27197d253d15e11e4f71b38cd Mon Sep 17 00:00:00 2001 From: Tara Overfield Date: Wed, 2 Sep 2026 14:26:08 -0700 Subject: [PATCH 7/7] Revise known issues for August 2026 update Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com> --- .../release-notes/2026/08-11-august-cumulative-update.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md index 5017d53121456..6d234374e6905 100644 --- a/docs/framework/release-notes/2026/08-11-august-cumulative-update.md +++ b/docs/framework/release-notes/2026/08-11-august-cumulative-update.md @@ -46,7 +46,7 @@ There are no new quality and reliability improvements in this release. ## Known issues in this release -#### Known Issue +#### Known issue After installing the August 2026 .NET Framework cumulative update, some Windows Presentation Foundation (WPF) applications might fail with a `System.IO.FileFormatException` when printing or generating PDF/XPS content that uses certain fonts, including Calibri.