Certutil.exe may download a file from a remote destination using
-urlcache. This behavior does require a URL to be passed on the command-line. In addition,
-f (force) and
-split (Split embedded ASN.1 elements, and save to files) will be used. It is not entirely common for
certutil.exe to contact public IP space. However, it is uncommon for
certutil.exe to write files to world writeable paths.\ During triage, capture any files on disk and review. Review the reputation of the remote IP or domain in question.
- Type: TTP
- Product: Splunk Behavioral Analytics
- Datamodel: Endpoint_Processes
- Last Updated: 2022-02-16
- Author: Michael Haag, Splunk
- ID: 8cb1ad38-8f6d-11ec-87a3-acde48001122
Kill Chain Phase
- CIS 8
1 2 3 4 5 6 7 8 | from read_ssa_enriched_events() | where "Endpoint_Processes" IN(_datamodels) | eval timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)), cmd_line=ucast(map_get(input_event, "process"), "string", null), process_name=ucast(map_get(input_event, "process_name"), "string", null), process_path=ucast(map_get(input_event, "process_path"), "string", null), parent_process_name=ucast(map_get(input_event, "parent_process_name"), "string", null), event_id=ucast(map_get(input_event, "event_id"), "string", null) | where cmd_line IS NOT NULL AND process_name IS NOT NULL AND process_name="certutil.exe" AND (like (cmd_line, "%urlcache%") AND like (cmd_line, "%split%")) OR (like (cmd_line, "%urlcache%")) | eval start_time=timestamp, end_time=timestamp, entities=mvappend(ucast(map_get(input_event, "dest_user_id"), "string", null), ucast(map_get(input_event, "dest_device_id"), "string", null)) | eval body=create_map(["event_id", event_id, "cmd_line", cmd_line, "process_name", process_name, "parent_process_name", parent_process_name, "process_path", process_path]) | into write_ssa_detected_events();
The SPL above uses the following Macros:
windows_certutil_urlcache_download_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
To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the
Endpoint datamodel in the
Known False Positives
Limited false positives in most environments, however tune as needed based on parent-child relationship or network connection.
Associated Analytic Story
|90.0||90||100||An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest_device_id$ by user $dest_user_id$ attempting to download a file.|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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