scan.c in x11vnc 0.9.16 uses IPC_CREAT|0777 in shmget calls, which allows access by actors other than the current user.
github.com/LibVNC/x11vnc/commit/69eeb9f7baa14ca03b16c9de821f9876def7a36a
lists.debian.org/debian-lts-announce/2020/12/msg00018.html
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/H2FLWSVH32O6JXLRQBYDQLP7XRSTLUPQ/
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MHVXHZE3YIP4RTWGQ24IDBSW44XPRDOC/
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PZL6NQTNK5PT63D2JX5YVV5OLUL76S5C/
www.debian.org/security/2020/dsa-4799