CVE-2021-22890: Authentication Bypass by Spoofing

curl to and including includes vulnerability that allows a malicious HTTPS proxy to MITM a connection due to bad handling of TLS session tickets. When using a HTTPS proxy and TLS, libcurl can confuse session tickets arriving from the HTTPS proxy but work as if they arrived from the remote server and then wrongly “short-cut” the host handshake. When confusing the tickets, a HTTPS proxy can trick libcurl to use the wrong session ticket resume for the host and thereby circumvent the server TLS certificate check and make a MITM attack to be possible to perform unnoticed. Note that such a malicious HTTPS proxy needs to provide a certificate that curl will accept for the MITMed server for an attack to work - unless curl has been told to ignore the server certificate check.