[pixl97]

This can go back to your old buddy NTP, specifically DHCP assigning this on untrusted networks. If you control the network (time?) and you manage to get the full expired certificate you may be able to MITM the victim successfully. If you force the CRL check first then things won't match up. I have no ideas on the feasibility of faking the CRL though, so it might be a wash.

[nijave]

Seems like it’d be fairly difficult in practice to change time on a host such that you can use an expired certificate without breaking a bunch of other stuff