BSD 4.4 based operating systems, when running at security level 1, allow the root user to clear the immutable and append-only flags for files by unmounting the file system and using a file system editor such as fsdb to directly modify the file through a device.

The asynchronous I/O facility in 4.4 BSD kernel does not check user credentials when setting the recipient of I/O notification, which allows local users to cause a denial of service by using certain ioctl and fcntl calls to cause the signal to be sent to an arbitrary process ID.