w3m through 0.5.3 is prone to a NULL pointer dereference flaw in formUpdateBuffer in form.c.
https://usn.ubuntu.com/3555-2/
https://usn.ubuntu.com/3555-1/
https://lists.debian.org/debian-lts-announce/2020/04/msg00025.html
https://github.com/tats/w3m/issues/89
https://github.com/tats/w3m/commit/7fdc83b0364005a0b5ed869230dd81752ba022e8
http://www.securityfocus.com/bid/102846
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00028.html