{"id":"CVE-2026-66822","kind":"vulnerability","aliases":["CVE-2026-66822","GHSA-wxxw-5cvc-53j7"],"related":[],"title":"Microsoft Security Advisory CVE-2026-66822 - .NET and Visual Studio Information Disclosure Vulnerability","description":"## Executive summary\n\nMicrosoft 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.\n\nSocketsHttpHandler can retain a `Proxy-Authorization` header across an HTTP redirect and leak basic proxy credentials to the destination server.\n\n## Announcement\n\nAnnouncement for this issue can be found at https://github.com/dotnet/announcements/issues/448\n\n## CVSS Details\n\n- **Version:** 3.1\n- **Severity:** Moderate\n- **Score:** 5.9\n- **Vector:** `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N`\n- **Weakness:** CWE-201 (Insertion of Sensitive Information Into Sent Data)\n\n## Affected Platforms\n\n- **Platforms:** Windows, Linux, macOS\n- **Architectures:** All\n\n## <a name=\"affected-packages\"></a>Affected Packages\n\nThe vulnerability affects Microsoft .NET projects that use an affected package version listed below.\n\nPackage name | Affected version | Patched version\n------------ | ---------------- | ---------------\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n[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\n\n## Advisory FAQ\n\n### <a name=\"how-affected\"></a>How do I know if I am affected?\n\nIf using a package listed in [affected packages](#affected-packages), you're exposed to the vulnerability.\n\n### <a name=\"how-fix\"></a>How do I fix the issue?\n\n1. 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.\n2. 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.\n\nOnce you have installed the updated runtime or SDK, restart your apps for the update to take effect.\n\nAdditionally, 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.\n\n## Other Information\n\n### Reporting Security Issues\n\nIf 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).\n\nSecurity 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.\n\n### Support\n\nYou 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.\n\n### Disclaimer\n\nThe 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.\n\n### External Links\n\n[CVE-2026-66822](https://www.cve.org/CVERecord?id=CVE-2026-66822)\n\n### Acknowledgements\n\n- Ky0toFu (@ky0tofu)\n- jhanks\n- Lucas Futures\n- Wenhan Zhou\n- Weeraphat Srisutham\n- Brent Woodard (@crusader_sec) with Crusader Security, LLC (https://crusaderproxy.com/)\n- Kevin Schmidt\n- Piotr Pietruszewski\n- Leandro Batista\n- Raffaello Tamagnini\n- Harkenzo\n- Anonymous\n- Attila.Cs (zerodaybugs.com) with https://zerodaybugs.com/\n- l8BL with ENKI WhiteHat (https://www.enki.co.kr/)\n- caveeroo (https://caveeroo.dev/) with Tarlogic (https://www.tarlogic.com/)\n\n### Revisions\n\nV1.0 (10/13/2026): Advisory published.","summary":"SocketsHttpHandler in .NET can keep a Proxy-Authorization header when following an HTTP redirect, so basic proxy credentials are sent to the redirect destination server. An attacker who can make the request land on a server they control, for example through a redirect they can influence, gets the proxy username and password.","severity":"medium","cvss":5.900000095367432,"epss":0.00674000009894371,"exploited":false,"exploited_at":null,"products":[{"name":"Microsoft.NETCore.App.Runtime.linux-arm","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-arm64","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-arm","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-arm64","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-x64","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-x64","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.osx-arm64","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.osx-x64","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-arm64","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-x64","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-x86","fixed":["9.0.21"],"affected":">= 9.0.0, <= 9.0.20","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-arm","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-arm64","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-arm","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-arm64","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-x64","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-x64","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.osx-arm64","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.osx-x64","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-arm64","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-x64","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-x86","fixed":["11.0.0-rc.2"],"affected":">= 11.0.0-preview.1, <= 11.0.0-rc.1","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-arm","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-arm64","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-arm","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-arm64","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-x64","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-x64","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.osx-arm64","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.osx-x64","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-arm64","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-x64","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-x86","fixed":["10.0.13"],"affected":">= 10.0.0, <= 10.0.12","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-arm","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-arm64","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-arm","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-arm64","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-musl-x64","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.linux-x64","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.osx-arm64","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.osx-x64","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-arm64","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-x64","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"},{"name":"Microsoft.NETCore.App.Runtime.win-x86","fixed":["8.0.32"],"affected":">= 8.0.0, <= 8.0.31","ecosystem":"nuget"}],"ecosystems":["nuget"],"tags":["cwe-201","dotnet","linux","macos","proxy-auth","runtime","self-hosted","windows"],"not_affected_if":["default-config","managed-hosting","no-proxy-credentials"],"how_to_check":"Run dotnet --info and check the installed Microsoft.NETCore.App runtime version; affected 9.0.x is 9.0.20 or lower, 10.0.x is 10.0.12 or lower, 8.0.x is 8.0.31 or lower, and 11.0 preview/rc through rc.1.\nList package references with dotnet list package and look for Microsoft.NETCore.App.Runtime.* at affected versions.\nCheck whether apps call HTTP through a proxy with credentials configured (HttpClientHandler Proxy or WebProxy with NetworkCredential).","fix":"Install the latest .NET runtime and SDK: 9.0.21 or later for 9.0, 10.0.13 or later for 10.0, 8.0.32 or later for 8.0, 11.0.0-rc.2 or later for 11 previews; restart apps and recompile and redeploy self-contained apps.\nUpdate Microsoft.NETCore.App.Runtime.* package references to the patched version.","status":"open","published_at":"2026-10-13T19:18:53+00:00","first_seen_at":"2026-10-23T19:11:32+00:00","triaged_at":"2026-10-23T19:58:01+00:00","updated_at":"2026-10-23T23:44:52+00:00","category":"runtime","confidence":0.8,"triage":{"at":"2026-10-23T19:58:01Z","model":"claude-haiku-5-5","output":{"fix":"Install the latest .NET runtime and SDK: 9.0.21 or later for 9.0, 10.0.13 or later for 10.0, 8.0.32 or later for 8.0, 11.0.0-rc.2 or later for 11 previews; restart apps and recompile and redeploy self-contained apps.\nUpdate Microsoft.NETCore.App.Runtime.* package references to the patched version.","summary":"SocketsHttpHandler in .NET can keep a Proxy-Authorization header when following an HTTP redirect, so basic proxy credentials are sent to the redirect destination server. An attacker who can make the request land on a server they control, for example through a redirect they can influence, gets the proxy username and password.","category":"runtime","who_cares":["dotnet","self-hosted","proxy-auth","windows","linux","macos"],"confidence":0.8,"analyst_note":"","how_to_check":"Run dotnet --info and check the installed Microsoft.NETCore.App runtime version; affected 9.0.x is 9.0.20 or lower, 10.0.x is 10.0.12 or lower, 8.0.x is 8.0.31 or lower, and 11.0 preview/rc through rc.1.\nList package references with dotnet list package and look for Microsoft.NETCore.App.Runtime.* at affected versions.\nCheck whether apps call HTTP through a proxy with credentials configured (HttpClientHandler Proxy or WebProxy with NetworkCredential).","needs_analyst":false,"not_affected_if":["default-config","no-proxy-credentials","managed-hosting"],"severity_if_unknown":"medium"},"cost_usd":0.001167,"input_tokens":8845,"output_tokens":564,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-201':138B,292C '-2026':5A,15A,23A '-66822':6A,16A,24A '/av':281C '/dotnet/announcements/issues/448':269C '/packages/microsoft.netcore.app.runtime.linux-arm)':334C,436C '/packages/microsoft.netcore.app.runtime.linux-arm64)':342C,447C '/packages/microsoft.netcore.app.runtime.linux-musl-arm)':352C,460C '/packages/microsoft.netcore.app.runtime.linux-musl-arm64)':362C,473C '/packages/microsoft.netcore.app.runtime.linux-musl-x64)':372C,486C '/packages/microsoft.netcore.app.runtime.linux-x64)':380C,497C '/packages/microsoft.netcore.app.runtime.osx-arm64)':388C,508C '/packages/microsoft.netcore.app.runtime.osx-x64)':396C '/packages/microsoft.netcore.app.runtime.win-arm)':404C '/packages/microsoft.netcore.app.runtime.win-arm64)':412C '/packages/microsoft.netcore.app.runtime.win-x64)':420C '/packages/microsoft.netcore.app.runtime.win-x86)':428C '11.0.0':437C,439C,441C,448C,450C,452C,461C,463C,465C,474C,476C,478C,487C,489C,491C,498C,500C,502C,509C '3.1':273C,280C '5.9':277C '53j7':21A '5cvc':20A '9.0.0':335C,343C,353C,363C,373C,381C,389C,397C,405C,413C,421C,429C '9.0.20':336C,344C,354C,364C,374C,382C,390C,398C,406C,414C,422C,430C '9.0.21':337C,345C,355C,365C,375C,383C,391C,399C,407C,415C,423C,431C 'across':245C 'advisori':3A,210C,220C 'affect':300C,308C,312C,319C,326C 'also':221C 'announc':258C,259C 'applic':232C 'architectur':306C 'arm':26A,32A,54A,60A,82A,88A,110A,116A,331C,349C,401C,433C,457C 'arm64':28A,36A,44A,48A,56A,64A,72A,76A,84A,92A,100A,104A,112A,120A,128A,132A,339C,359C,385C,409C,444C,470C,505C 'attack':177B 'auth':144B 'author':158B,243C 'basic':166B,251C 'control':188B 'credenti':168B,253C 'cve':4A,14A,22A 'cvss':270C,279C 'cwe':137B,291C 'data':299C 'destin':174B,256C 'detail':271C 'develop':226C 'disclosur':12A 'dotnet':139B 'exampl':190B 'execut':203C 'follow':161B 'found':265C 'get':197B 'ghsa':18A 'ghsa-wxxw-5cvc-53j7':17A 'github.com':268C 'github.com/dotnet/announcements/issues/448':267C 'guidanc':223C 'h/i':287C 'h/pr':283C 'header':159B,244C 'host':148B 'http':163B,247C 'influenc':196B 'inform':11A,213C,296C 'insert':293C 'issu':262C 'keep':154B 'land':183B 'leak':250C 'linux':140B,304C 'list':322C 'maco':141B,305C 'make':180B 'microsoft':1A,205C,313C 'microsoft.netcore.app.runtime.linux':25A,27A,29A,33A,37A,41A,53A,55A,57A,61A,65A,69A,81A,83A,85A,89A,93A,97A,109A,111A,113A,117A,121A,125A,330C,338C,346C,356C,366C,376C,432C,443C,454C,467C,480C,493C 'microsoft.netcore.app.runtime.osx':43A,45A,71A,73A,99A,101A,127A,129A,384C,392C,504C 'microsoft.netcore.app.runtime.win':47A,49A,51A,75A,77A,79A,103A,105A,107A,131A,133A,135A,400C,408C,416C,424C 'moder':275C 'musl':31A,35A,39A,59A,63A,67A,87A,91A,95A,115A,119A,123A,348C,358C,368C,456C,469C,482C 'musl-arm':30A,58A,86A,114A,347C,455C 'musl-arm64':34A,62A,90A,118A,357C,468C 'musl-x64':38A,66A,94A,122A,367C,481C 'n':289C 'n/a':288C 'n/ac':282C 'n/s':285C 'n/ui':284C 'name':325C 'net':7A,152B,314C 'packag':309C,320C,324C 'password':202B 'patch':328C 'platform':301C,302C 'pre':510C 'preview.1':438C,449C,462C,475C,488C,499C 'project':315C 'provid':212C,222C 'proxi':143B,157B,167B,199B,242C,252C 'proxy-auth':142B 'proxy-author':156B,241C 'rc.1':440C,451C,464C,477C,490C,501C 'rc.2':442C,453C,466C,479C,492C,503C 'redirect':164B,173B,193B,248C 'releas':207C 'remov':234C 'request':182B 'retain':239C 'runtim':145B 'score':276C 'secur':2A,209C 'self':147B 'self-host':146B 'sensit':295C 'sent':170B,298C 'server':175B,186B,257C 'sever':274C 'socketshttphandl':150B,237C 'studio':10A 'summari':204C 'system.net.http':218C 'u/c':286C 'updat':230C 'use':317C 'usernam':200B 'vector':278C 'version':272C,321C,327C,329C 'visual':9A 'vulner':13A,216C,236C,311C 'weak':290C 'window':149B,303C 'www.nuget.org':333C,341C,351C,361C,371C,379C,387C,395C,403C,411C,419C,427C,435C,446C,459C,472C,485C,496C,507C 'www.nuget.org/packages/microsoft.netcore.app.runtime.linux-arm)':332C,434C 'www.nuget.org/packages/microsoft.netcore.app.runtime.linux-arm64)':340C,445C 'www.nuget.org/packages/microsoft.netcore.app.runtime.linux-musl-arm)':350C,458C 'www.nuget.org/packages/microsoft.netcore.app.runtime.linux-musl-arm64)':360C,471C 'www.nuget.org/packages/microsoft.netcore.app.runtime.linux-musl-x64)':370C,484C 'www.nuget.org/packages/microsoft.netcore.app.runtime.linux-x64)':378C,495C 'www.nuget.org/packages/microsoft.netcore.app.runtime.osx-arm64)':386C,506C 'www.nuget.org/packages/microsoft.netcore.app.runtime.osx-x64)':394C 'www.nuget.org/packages/microsoft.netcore.app.runtime.win-arm)':402C 'www.nuget.org/packages/microsoft.netcore.app.runtime.win-arm64)':410C 'www.nuget.org/packages/microsoft.netcore.app.runtime.win-x64)':418C 'www.nuget.org/packages/microsoft.netcore.app.runtime.win-x86)':426C 'wxxw':19A 'x64':40A,42A,46A,50A,68A,70A,74A,78A,96A,98A,102A,106A,124A,126A,130A,134A,369C,377C,393C,417C,483C,494C 'x86':52A,80A,108A,136A,425C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-13T19:18:53+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N","cvss_by":"GitHub","poc_count":0,"sources":[{"source":"ghsa","external_id":"GHSA-wxxw-5cvc-53j7","url":"https://github.com/advisories/GHSA-wxxw-5cvc-53j7","severity":"medium","published_at":"2026-10-13T20:41:40+00:00","modified_at":"2026-10-19T19:19:00+00:00","first_seen_at":"2026-10-23T19:11:32+00:00","fetched_at":"2026-10-23T19:11:32+00:00","note":null},{"source":"nvd","external_id":"CVE-2026-66822","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-66822","severity":null,"published_at":"2026-10-13T19:18:53+00:00","modified_at":"2026-10-22T22:18:07+00:00","first_seen_at":"2026-10-23T23:44:52+00:00","fetched_at":"2026-10-23T23:44:52+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}