setuid Permission

When set-user identification (setuid) permission is set on an executable file, a process that runs this file is granted access based on the owner of the file (usually root), rather than the user who is running the executable file. This allows a user to access files and directories that are normally only available to the owner. For example, the setuid permission on the passwd command makes it possible for a user to change passwords, assuming the permissions of the root ID:

-r-sr-sr-x   3 root     sys       104580 Sep 16 12:02 /usr/bin/passwd

This presents a security risk, because some determined users can find a way to maintain the permissions granted to them by the setuid process even after the process has finished executing.

Using setuid permissions with the reserved UIDs (0-99) from a program might not set the effective UID correctly. Use a shell script instead or avoid using the reserved UIDs with setuid permissions.