Linux Possible Append Command To At Allow Config File

The analytic detects suspicious command lines that append user entries to `/etc/at.allow` or `/etc/at.deny` files on Linux systems. This activity is significant because altering these configuration files can allow attackers to schedule tasks with elevated permissions, facilitating persistence on a compromised Linux host. If confirmed malicious, this could enable attackers to execute arbitrary code at scheduled intervals, potentially leading to further system compromise and unauthorized access to sensitive information. The rule specifically looks for `echo` commands writing to these files.