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Description

The following analytic identifies .cab files being written to disk. Utilize this analytic as a way to hunt for suspect .cab files being written to non-standard paths and tune as needed. Cab files were recently being utilized to deliver .url files embedded. The .url files were then used to deliver malicious payloads. The search specifically looks for instances where the file name is '*.cab' and the action is 'write'. During the triage process, it is recommended to review the file path for additional artifacts that may provide further insights into the event.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2023-11-08
  • Author: Michael Haag, Splunk
  • ID: 622f08d0-69ef-42c2-8139-66088bc25acd

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1566.001 Spearphishing Attachment Initial Access
Kill Chain Phase
  • Delivery
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


1
2
3
4
5
6



| tstats `security_content_summariesonly` count values(Filesystem.file_path) as file_path min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Filesystem where (Filesystem.file_name=*.cab) by Filesystem.dest Filesystem.action Filesystem.process_id Filesystem.file_name 
| `drop_dm_object_name("Filesystem")` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_cab_file_on_disk_filter`

Macros

The SPL above uses the following Macros:

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

Required fields

List of fields required to use this analytic.

  • Filesystem.dest
  • Filesystem.action
  • Filesystem.process_id
  • Filesystem.file_name

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

False positives will only be present if a process legitimately writes a .cab file to disk. Modify the analytic as needed by file path. Filter as needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
5.0 50 10 A .cab file was written to disk on endpoint $dest$.

: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

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