Microsoft Security Advisory CVE-2026-66822 - .NET and Visual Studio Information Disclosure Vulnerability
The source advisory has changed since this explanation was prepared. Check the current technical data and original advisory below.
Executive Summary
Microsoft has released a security advisory regarding a vulnerability in System.Net.Http. SocketsHttpHandler can retain a Proxy-Authorization header across an HTTP redirect, potentially leaking basic proxy credentials to the destination server.
Announcement
The announcement for this issue is available at https://github.com/dotnet/announcements/issues/448.
CVSS Details
- Version: 3.1
- Severity: Moderate
- Score: 5.9
- Vector:
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N - Weakness: CWE-201 (Insertion of Sensitive Information Into Sent Data)
Affected Platforms
- Platforms: Windows, Linux, macOS
- Architectures: All
Affected Packages
This vulnerability impacts Microsoft .NET projects utilizing any of the affected package versions listed below:
Advisory FAQ
How do I know if I am affected?
If using a package listed in the affected packages table above, you are exposed to the vulnerability.
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
Acknowledgements
- Ky0toFu (@ky0tofu)
- jhanks
- Lucas Futures
- Wenhan Zhou
- Weeraphat Srisutham
- Brent Woodard (@crusader_sec) with Crusader Security, LLC (https://crusaderproxy.com/))
- Kevin Schmidt
- Piotr Pietruszewski
- Leandro Batista
- Raffaello Tamagnini
- Harkenzo
- Anonymous
- Attila.Cs (zerodaybugs.com) with https://zerodaybugs.com/
- l8BL with ENKI WhiteHat (https://www.enki.co.kr/))
- caveeroo (https://caveeroo.dev/)) with Tarlogic (https://www.tarlogic.com/))
Revisions
V1.0 (10/13/2026): Advisory published.
What to do
To resolve the vulnerability, take the following steps:
- Install the latest version of .NET. If you have installed one or more .NET SDKs through Visual Studio, Visual Studio will prompt you to update Visual Studio, which will also update your .NET SDKs.
- If your application references the vulnerable package, update the package reference to the patched version. You can list the versions you have installed by running the
dotnet --infocommand.
Once you have installed the updated runtime or SDK, restart your apps for the update to take effect.
Additionally, if you have deployed self-contained applications) targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.linux-arm | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.linux-arm64 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.linux-musl-x64 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.linux-x64 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.osx-arm64 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.osx-x64 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.win-arm64 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.win-x64 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
| .NET (NuGet) | Microsoft.NETCore.App.Runtime.win-x86 | >= 9.0.0, < 9.0.21, >= 11.0.0-preview.1, < 11.0.0-rc.2, >= 10.0.0, < 10.0.13, >= 8.0.0, < 8.0.32 | 9.0.21, 11.0.0-rc.2, 10.0.13, 8.0.32 |
References
- https://github.com/dotnet/runtime/security/advisories/GHSA-wxxw-5cvc-53j7
- https://github.com/dotnet/announcements/issues/448
- https://github.com/dotnet/runtime/issues/135697
- https://github.com/dotnet/runtime
- https://nvd.nist.gov/vuln/detail/CVE-2026-66822
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66822
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N- Weakness (CWE)
CWE-201- Platform
- .NET (NuGet)
- Package
Microsoft.NETCore.App.Runtime.linux-arm, Microsoft.NETCore.App.Runtime.linux-arm64, Microsoft.NETCore.App.Runtime.linux-musl-arm- Disclosed
- 13.10.2026
- Updated
- 19.10.2026 22:17
Sources and licenses · Edited or translated by DockRay; source rights and applicable licenses are retained.
OSV / GitHub Advisory Database - GHSA-wxxw-5cvc-53j7 - CC BY 4.0
Vulnerability history: Microsoft.NETCore.App.Runtime.linux-x64
All published vulnerabilities of this package (.NET (NuGet)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 36
- First → latest
- 09.2020 10.2026
- Without a fix
- 0
- Exploited in attacks
- 1
Severity breakdown
- High 22
- Medium 13
- Low 1
Disclosures per year
- 2020: 1
- 2021: 0
- 2022: 6
- 2023: 5
- 2024: 4
- 2025: 5
- 2026: 15
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Microsoft Security Advisory CVE-2026-66822 - .NET and Visual Studio Information Disclosure Vulnerability this entry
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