Windows System Binary Proxy Execution Compiled HTML File URL In Command Line
The following analytic identifies hh.exe (HTML Help) execution of a Compiled HTML Help (CHM) file from a remote url. This particular technique will load Windows script code from a compiled help file. CHM files may contain nearly any file type embedded, but only execute html/htm. Upon a successful execution, the following script engines may be used for execution - JScript, VBScript, VBScript.Encode, JScript.Encode, JScript.Compact. Analyst may identify vbscript.dll or jscript.dll loading into hh.exe upon execution. The "htm" and "html" file extensions were the only extensions observed to be supported for the execution of Shortcut commands or WSH script code. During investigation, identify script content origination. Review reputation of remote IP and domain. Some instances, it is worth decompiling the .chm file to review its original contents. hh.exe is natively found in C:\Windows\system32 and C:\Windows\syswow64.
- Type: TTP
Product: Splunk Behavioral Analytics
- Last Updated: 2022-09-02
- Author: Michael Haag, Splunk
- ID: 0fec631a-7c9b-4e4c-b28b-93260953e25f
Kill Chain Phase
- CIS 10
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 | from read_ba_enriched_events() | eval timestamp = ucast(map_get(input_event,"time"),"long", null) | eval metadata = ucast(map_get(input_event, "metadata"),"map<string, any>", null) | eval metadata_uid = ucast(map_get(metadata, "uid"),"string", null) | eval process=ucast(map_get(input_event,"process"), "map<string, any>", null) | eval process_pid=ucast(map_get(process,"pid"), "string", null) | eval process_file=ucast(map_get(process,"file"), "map<string, any>", null) | eval process_file_path=ucast(map_get(process_file,"path"), "string", null) | eval process_file_name=ucast(map_get(process_file,"name"), "string", null) | eval process_cmd_line=ucast(map_get(process,"cmd_line"), "string", null) | eval actor=ucast(map_get(input_event,"actor"), "map<string, any>", null) | eval actor_user=ucast(map_get(actor,"user"), "map<string, any>", null) | eval actor_user_name=ucast(map_get(actor_user,"name"), "string", null) | eval actor_process=ucast(map_get(actor,"process"), "map<string, any>", null) | eval actor_process_pid=ucast(map_get(actor_process,"pid"), "string", null) | eval actor_process_file=ucast(map_get(actor_process,"file"), "map<string, any>", null) | eval actor_process_file_path=ucast(map_get(actor_process_file,"path"), "string", null) | eval actor_process_file_name=ucast(map_get(actor_process_file,"name"), "string", null) | eval device=ucast(map_get(input_event,"device"), "map<string, any>", null) | eval device_hostname=ucast(map_get(device,"hostname"), "string", null) | where (like(process_cmd_line, "%https://%") OR like(process_cmd_line, "%http://%")) AND process_file_name="hh.exe" --finding_report--
The SPL above uses the following Macros:
windows_system_binary_proxy_execution_compiled_html_file_url_in_command_line_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 logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.
Known False Positives
Although unlikely, some legitimate applications may retrieve a CHM remotely, filter as needed.
Associated Analytic Story
|90.0||90||100||An instance of $process_name$ was identified on endpoint $dest_device_id$ by user $dest_user_id$ contacting a remote destination.|
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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