The rule titled 'Authentication via Unusual PAM Grantor' aims to detect successful authentication events on Linux systems using Pluggable Authentication Modules (PAM) grantors that are not commonly utilized. Such unusual grantors may indicate potential malicious activities where an attacker is trying to elevate their privileges or establish persistence on the system by modifying the standard PAM configuration. It utilizes the 'auditd_manager' integration to gather real-time events and identify these irregular authentication attempts. The rule operates on data from both Auditbeat and AuditD logs, specifically looking for authentications that are successful but involve unconventional PAM grantors excluding common ones like 'pam_rootok' or any PAM capabilities that might be typical in secure environments. The detection rule also includes a comprehensive investigation guide for analyzing incidents, where it suggests checking for known grantors, user activities, and any unauthorized changes to PAM configurations. Organizations are encouraged to look for false positives that may arise due to customization or specific applications that use unusual PAM modules, thus allowing for legitimate exceptions in their alerting system.