In kex.c:kex_input_kexinit, when a packet with the other side's KEX proposal is received, it is appended into a buffer that has not been cleared first. This could lead to problems - in particular, if that buffer already contains an old peer proposal, the new one will be appended but the old one will be silently used instead.

The code is currently:

    ptr = packet_get_raw(&dlen);
    buffer_append(&kex->peer, ptr, dlen);

but should be:

    ptr = packet_get_raw(&dlen);
    buffer_clear(&kex->peer);
    buffer_append(&kex->peer, ptr, dlen);