In OpenBSD 7.3 before errata 016, npppd(8) could crash by a l2tp message which has an AVP (Attribute-Value Pair) with wrong length.
https://github.com/openbsd/src/commit/abf3a29384c582c807a621e7fc6e7c68d0cafe9b
https://ftp.openbsd.org/pub/OpenBSD/patches/7.3/common/016_npppd.patch.sig