Depends on which Microsoft OS and user agent. If, e.g., you're using an unpatched Windows 8.1 with IE11, you'll still be able to connect initially but will get

Depends on which Microsoft OS and user agent. If, e.g., you're using an unpatched Windows 8.1 with IE11, you'll still be able to connect initially but will get disconnected the first time the key is rotated (max of 1 hour). Upon disconnection, IE11 will downgrade from TLS 1.2 to 1.0 and try again with a new session, so the user probably won't notice anything unless they're looking for it. That being said, many sites are starting to deprecate TLS 1.0, so this could become more of a problem for patch laggards. If, instead, you're using a .NET client that doesn't try/catch the exception, your program will most likely crash. For customers like this with had a high dependency on Microsoft clients, we simply disabled the issuance of session tickets (just for their site) until the fix was made public. Basically, SChannel freaks out when it sees a new session ticket presented during the abbreviated handshake (it handles it fine during the full handshake). Without seeing their code, it appears that only portions of RFC 5077 were implemented. Btw, most sites don't ever bother to ever rotate their session ticket keys outside of httpd process restarts, so this is why it wasn't discovered for so long.