The following analytic is designed to identify suspicious command lines that may append user entries to either /etc/at.allow or /etc/at.deny. These files can be exploited by malicious actors for persistence on a compromised Linux host by altering permissions for scheduled tasks using the at command.
In this context, an attacker can create a user or add an existing user to these configuration files to execute their malicious code through scheduled tasks. The detection of such anomalous behavior can serve as an effective indicator warranting further investigation to validate if the activity is indeed malicious or 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
Kill Chain Phase
- CIS 10
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`
The SPL above uses the following Macros:
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.
List of fields required to use this analytic.
How To Implement
The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the
Processes node of the
Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
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
|9.0||30||30||A commandline $process$ that may modify at allow config file in $dest$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
source | version: 2