The following command, when run as any user, will crash systemd. The bug is remarkably banal but serious, as it allows any local user to trivially perform a denial-of-service attack against a critical system component. Writing bug-free software is extremely difficult, but good programmers would inevitably introduce bugs into a project of the scale and complexity of Systemd. Systemd’s “we don’t make mistakes” attitude towards security can be seen in other places, such as this code from the main function of PID 1: Setting a umask of 0 means by default, by setting a macro that creates a more restrictive file that works twice a potential vulnerability.”]
Source: https://www.agwa.name/blog/post/how_to_crash_systemd_in_one_tweet