sppp_pap_input in sys/net/if_spppsubr.c in OpenBSD before 076e2b1 allows authentication bypass via certain zero values for lengths.
Exploitability
AV:AAC:HPR:NUI:NScope
S:CImpact
C:LI:LA:L5.8/CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:LOther