NetBSD 1.4.2 and earlier allows local users to cause a denial of service by repeatedly running certain system calls in the kernel which do not yield the CPU, aka "cpu-hog".
ftpd in NetBSD 1.4.2 does not properly parse entries in /etc/ftpchroot and does not chroot the specified users, which allows those users to access other files outside of their home directory.
FreeBSD, NetBSD, and OpenBSD allow an attacker to cause a denial of service by creating a large number of socket pairs using the socketpair function, setting a large buffer size via setsockopt, then writing large buffers.
Operating systems with shared memory implementations based on BSD 4.4 code allow a user to conduct a denial of service and bypass memory limits (e.g., as specified with rlimits) using mmap or shmget to allocate memory and cause page faults.