CVE-2026-66822: Microsoft Security Advisory CVE-2026-66822 - .NET and Visual Studio Information Disclosure Vulnerability

October 13, 2026 (updated October 19, 2026)

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.

References

github.com/advisories/GHSA-wxxw-5cvc-53j7
github.com/dotnet/announcements/issues/448
github.com/dotnet/runtime/issues/135697
github.com/dotnet/runtime/security/advisories/GHSA-wxxw-5cvc-53j7
msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66822
nvd.nist.gov/vuln/detail/CVE-2026-66822

Code Behaviors & Features

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