Installing WiringPi from the official Raspbian repositories (on Stretch or later, I believe) will create an executable file at /usr/bin/gpio.

• By default, the owner of the file is root, i.e. 0, and the group is root, i.e. 0.
• By default, the permissions on the file is 4755. The interesting part of this is the 4, which is the setuid bit. It enables executables to be run with the same privileges as the file's owner, in this case 0, or root.

I fixed the problem simply by removing the setuid bit with chmod 0755 $(which gpio). GPIO can now only be controlled by the root user, even if a user is a member of the gpio group. Considering that there are other groups like i2c and spi, I'm not sure if this completely mitigates security problems.

Installing WiringPi from the official Raspbian repositories (on Stretch or later, I believe) will create an executable file at /usr/bin/gpio.

• By default, the owner of the file is root, i.e. 0, and the group is root, i.e. 0.
• By default, the permissions on the file is 4755. The interesting part of this is the 4, which is the setuid bit. It enables executables to be run with the same privileges as the file's owner, in this case 0, or root.

I fixed the problem simply by removing the setuid bit with chmod 0755 $(which gpio). GPIO can now only be controlled by the root user, even if a user is a member of the gpio group. Considering that there are other groups like i2c and spi, I'm not sure if this completely mitigates security problems.

I wish the gpio group could enable/disable GPIO control for users.