Message of the day (MOTD) is the message that is presented to the user when a user connects to a Linux server via SSH or a serial connection. Linux systems contain several default MOTD files located in the "/etc/update-motd.d/" and "/usr/lib/update-notifier/" directories. These scripts run as the root user every time a user connects over SSH or a serial connection. Adversaries may create malicious MOTD files that grant them persistence onto the target every time a user connects to the system by executing a backdoor script or command. This rule detects the creation of potentially malicious files within the default MOTD file directories.

Rule type: new_terms

Rule indices:

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

Version: 2

Rule authors:

Rule license: Elastic License v2

host.os.type :"linux" and event.action:("creation" or "file_create_event" or "rename" or "file_rename_event") and
file.path : (/etc/update-motd.d/* or /usr/lib/update-notifier/*) and not
process.executable : ("/usr/bin/dpkg" or "/usr/bin/dockerd" or "/bin/rpm") and not
file.extension : "swp"