ec2-user    ALL = NOPASSWD: ALL

sudo: /etc/sudoers is world writable
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin

pkexec chmod 0440 /etc/sudoers

==== AUTHENTICATING FOR org.freedesktop.policykit.exec ===
Authentication is needed to run `/usr/bin/chmod' as the super user
Authenticating as: Cloud User (ec2-user)
Password:

polkit-agent-helper-1: pam_authenticate failed: Authentication failure
==== AUTHENTICATION FAILED ===
Error executing command as another user: Not authorized

This incident has been reported.

mount -uw /;mount -o remount,rw /;chmod 440 /etc/sudoers