According to this page [1], they already support RFC 5246, which is supposed to be TLS 1.2 compliant. The code on github seems to indicate that they've at least implemented HMAC-SHA256 [2] and the mandatory TLS_RSA_WITH_AES_128_CBC_SHA [3] from TLS 1.2, judging by my cursory glance. You can probably find the rest by searching the repo for yourself.
[1] https://www.softether.org/3-spec
[2] https://github.com/SoftEtherVPN/SoftEth ... /Encrypt.c
[3] https://github.com/SoftEtherVPN/SoftEth ... ssl/tls1.h