cURL Schannel TLS 1.3 bug on Windows

November 9, 2022

We helped discover a cURL bug when using native Schannel TLS 1.3 support on Windows for cURL 7.85 and 7.86. The symptoms include that downloads may fail on Windows 11 with TLS 1.3 enabled on HTTPS or other TLS 1.3 server downloads. The bug is revealed when building cURL on Windows using Schannel. We first observed this in CMake 3.25.0-rc3,rc4 that use vendored cURL 7.86.