Linux: Job Schedule Modification

Rule ID

PH_Rule_TH_EQLLIB_LINUX_13

Default Status

Enabled

Description

Detects attempt to create pre-scheduled and periodic background jobs on Linux systems by modifying crontab files

Severity

MITRE ATT&CK® Tactics

Persistence

Persistence consists of techniques that adversaries use to keep access to systems across restarts, changed credentials, and other interruptions that could cut off their access. Techniques used for persistence include any access, action, or configuration changes that let them maintain their foothold on systems, such as replacing or hijacking legitimate code or adding startup code.

https://attack.mitre.org/tactics/TA0003

MITRE ATT&CK® Techniques

T1053.003

Scheduled Task/Job: Cron

Adversaries may abuse the cron utility to perform task scheduling for initial or recurring execution of malicious code. The cron utility is a time-based job scheduler for Unix-like operating systems. An adversary may use cron in Linux or Unix environments to execute programs at system startup or on a scheduled basis for persistence.

https://attack.mitre.org/techniques/T1053/003

Impacts

Server

Data Source

Linux File Monitoring via FortiSIEM Agent

Detection

Correlation

Remediation Guidance

No remediation guidance specified

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

Filter

SubPattern Definitions

SubPattern Name: Filter

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType REGEXP "FSM_LINUX_FILE_.*" AND targetOsObjName REGEXP ".*LaunchDaemons.*|/etc/cron\.d|/etc/crontab"

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

hostName,targetOsObjName

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT(*) >= 1

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

 hostName = Filter.hostName,
targetOsObjName = Filter.targetOsObjName

FortiSIEM Rules