GHSA-xhj5-c3g8-pfj8: Microsoft Security Advisory CVE-2026-109476 - ASP.NET Core Information Disclosure Vulnerability

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core. This advisory provides guidance on updating affected applications and components.

A crafted X-Forwarded-Prefix can inject cookie path delimiters unless PathBase-derived cookie paths percent-encode semicolons.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/508

CVSS Details

- Version: 3.1 - Severity: Medium - Score: 6.1 (base score) - Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:N/A:N/E:U/RL:O/RC:C - Weakness: CWE-116

Affected Platforms

- Platforms: Windows, Linux, macOS - Architectures: All

<a name="affected-packages"></a>Affected Packages

The tables list affected version ranges and fixed package versions. Runtime and standalone deliveries are listed separately.

.NET 8.0 - affected runtime packages

Package | Affected version | Patched version --- | --- | --- Microsoft.AspNetCore.App.Runtime.linux-arm | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.linux-arm64 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.linux-musl-arm | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.linux-musl-x64 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.osx-x64 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.win-arm64 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.win-x64 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34 Microsoft.AspNetCore.App.Runtime.win-x86 | >= 8.0.0-rc.1.23421.29, <= 8.0.33 | 8.0.34

.NET 9.0 - affected runtime packages

Package | Affected version | Patched version --- | --- | --- Microsoft.AspNetCore.App.Runtime.linux-arm | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.linux-arm64 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.linux-musl-arm | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.linux-musl-x64 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.osx-x64 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.win-arm64 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.win-x64 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23 Microsoft.AspNetCore.App.Runtime.win-x86 | >= 9.0.0-preview.1.24081.5, <= 9.0.22 | 9.0.23

.NET 10.0 - affected runtime packages

Package | Affected version | Patched version --- | --- | --- Microsoft.AspNetCore.App.Runtime.linux-arm | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.linux-arm64 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.linux-musl-arm | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.linux-musl-x64 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.osx-x64 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.win-arm64 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.win-x64 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15 Microsoft.AspNetCore.App.Runtime.win-x86 | >= 10.0.0-preview.1.25120.3, <= 10.0.14 | 10.0.15

.NET 11.0 - affected runtime packages

Package | Affected version | Patched version --- | --- | --- Microsoft.AspNetCore.App.Runtime.linux-arm | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.linux-arm64 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.linux-musl-arm | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.linux-musl-arm64 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.linux-musl-x64 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.linux-x64 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.osx-arm64 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.osx-x64 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.win-arm64 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.win-x64 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0 Microsoft.AspNetCore.App.Runtime.win-x86 | >= 11.0.0-preview.1.26104.118, <= 11.0.0-rc.3.26522.148 | 11.0.0

Advisory FAQ

<a name="how-affected"></a>How do I know if I am affected?

Check the deployed runtime and application package versions against the affected ranges above. Self-contained applications include their own runtime; updating a machine-wide runtime does not replace it.

<a name="how-fix"></a>How do I fix the issue?

Install the applicable runtime or update each independently referenced package to the fixed version above. Restart applications. Rebuild and redeploy self-contained applications; updating a machine-wide runtime does not replace their embedded runtime. An SDK update alone does not update an application's standalone package references.

Other Information

Reporting Security Issues

If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.

Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.

Support

You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repos are located at https://github.com/dotnet/runtime. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue.

Disclaimer

The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

External Links

CVE-2026-109476

Acknowledgements

- Raffaello Tamagnini

Revisions

V1.0 (November 10, 2026): Advisory published.