sudo gives 'PERM_SUDOERS: setresuid(-1, 1, -1): Operation not permitted' error

Issue

• Running the sudo command fails with the following error:

$ sudo su -
sudo: PERM_SUDOERS: setresuid(-1, 1, -1): Operation not permitted
sudo: no valid sudoers sources found, quitting
sudo: setresuid() [0, 0, 0] -> [505, -1, -1]: Operation not permitted
sudo: unable to initialize policy plugin

• The problem happens if we login as a non-root user and then run sudo, but it works fine if we run su - testuser when logged in as root.