.NET Information Disclosure Vulnerability

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

Insertion of sensitive information into sent data in .NET allows an unauthorized attacker to disclose information over a network.

Source published

13 Oct 2026 18:59:44 UTC

Source modified

31 Oct 2026 18:02:27 UTC

Observed here

31 Oct 2026 20:04:47 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C

Insertion of sensitive information into sent data in .NET allows an unauthorized attacker to disclose information over a network.

Source published

Oct 13, 2026, 6:59:44 PM (timezone not stated)

Source modified

Oct 31, 2026, 6:02:27 PM (timezone not stated)

Observed here

7 Nov 2026 13:32:27 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C

Insertion of sensitive information into sent data in .NET allows an unauthorized attacker to disclose information over a network.

Source published

13 Oct 2026 19:18:53 UTC

Source modified

22 Oct 2026 22:18:07 UTC

Observed here

25 Oct 2026 15:18:51 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

## Executive summary Microsoft is releasing this security advisory to provide information about a vulnerability in System.Net.Http. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability. SocketsHttpHandler can retain a `Proxy-Authorization` header across an HTTP redirect and leak basic proxy credentials to the destination server. ## Announcement Announcement for this issue can be found 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 ## <a name="affected-packages"></a>Affected Packages The vulnerability affects Microsoft .NET projects that use an affected package version listed below. Package name | Affected version | Patched version ------------ | ---------------- | --------------- [Microsoft.NETCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm64) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-arm) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-arm64) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-x64) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-x64) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.osx-arm64) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.osx-x64) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-arm) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-arm64) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.win-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-x64) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.win-x86](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-x86) | >= 9.0.0, <= 9.0.20 | 9.0.21 [Microsoft.NETCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm64) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-arm) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-arm64) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-x64) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-x64) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.osx-arm64) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.osx-x64) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-arm) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-arm64) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.win-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-x64) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.win-x86](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-x86) | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 [Microsoft.NETCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm64) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-arm) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-arm64) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-x64) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-x64) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.osx-arm64) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.osx-x64) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-arm) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-arm64) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.win-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-x64) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.win-x86](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-x86) | >= 10.0.0, <= 10.0.12 | 10.0.13 [Microsoft.NETCore.App.Runtime.linux-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.linux-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-arm64) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-arm) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.linux-musl-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-arm64) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.linux-musl-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-musl-x64) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.linux-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.linux-x64) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.osx-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.osx-arm64) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.osx-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.osx-x64) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.win-arm](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-arm) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.win-arm64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-arm64) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.win-x64](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-x64) | >= 8.0.0, <= 8.0.31 | 8.0.32 [Microsoft.NETCore.App.Runtime.win-x86](https://www.nuget.org/packages/Microsoft.NETCore.App.Runtime.win-x86) | >= 8.0.0, <= 8.0.31 | 8.0.32 ## Advisory FAQ ### <a name="how-affected"></a>How do I know if I am affected? If using a package listed in [affected packages](#affected-packages), you're exposed to the vulnerability. ### <a name="how-fix"></a>How do I fix the issue? 1. To fix the issue please 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. 2. 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 --info` command. Once you have installed the updated runtime or SDK, restart your apps for the update to take effect. Additionally, if you've deployed [self-contained applications](https://docs.microsoft.com/dotnet/core/deploying/#self-contained-deployments-scd) targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed. ## 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](https://msrc.microsoft.com/report/vulnerability/new). Further information can be found in the MSRC [Report an Issue FAQ](https://www.microsoft.com/msrc/faqs-report-an-issue). 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-2026-66822](https://www.cve.org/CVERecord?id=CVE-2026-66822) ### 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.

Source published

13 Oct 2026 20:41:40 UTC

Source modified

19 Oct 2026 19:30:30 UTC

Observed here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Publisher rating · MODERATE