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Description

This analytic looks for suspicious commandline that may use to append user entry to /etc/at.allow or /etc/at.deny. These 2 files are commonly abused by malware, adversaries or red teamers to persist on the targeted or compromised host. These config file can restrict user that can only execute at application (another schedule task application in linux). attacker can create a user or add the compromised username to that config file to execute at to schedule it malicious code. This anomaly detection can be a good indicator to investigate further the entry in created config file and who created it to verify if it is a false positive.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2022-05-26
  • Author: Teoderick Contreras, Splunk
  • ID: 7bc20606-5f40-11ec-a586-acde48001122

Annotations

ATT&CK
ID Technique Tactic
T1053.002 At Execution, Persistence, Privilege Escalation
T1053 Scheduled Task/Job Execution, Persistence, Privilege Escalation
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 3
  • CIS 5
  • CIS 16
CVE
1
2
3
4
5
6
| tstats `security_content_summariesonly` count from datamodel=Endpoint.Processes where Processes.process = "*echo*" AND Processes.process IN("*/etc/at.allow", "*/etc/at.deny") by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id Processes.process_guid 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `linux_possible_append_command_to_at_allow_config_file_filter`

Macros

The SPL above uses the following Macros:

:information_source: linux_possible_append_command_to_at_allow_config_file_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required field

  • _time
  • Processes.dest
  • Processes.user
  • Processes.parent_process_name
  • Processes.process_name
  • Processes.process
  • Processes.process_id
  • Processes.parent_process_id

How To Implement

To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you can use the Add-on for Linux Sysmon from Splunkbase.

Known False Positives

Administrator or network operator can use this commandline for automation purposes. Please update the filter macros to remove false positives.

Associated Analytic story

RBA

Risk Score Impact Confidence Message
9.0 30 30 A commandline $process$ that may modify at allow config file in $dest$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

source | version: 2