Detection rules › Splunk
Suspicious Child Process for hh.exe (Sysmon)
Adversaries may abuse Compiled HTML files (.chm) to conceal malicious code. CHM files are commonly distributed as part of the Microsoft HTML Help system. A custom CHM file containing embedded payloads could be delivered to a victim then triggered by User Execution. This use case detects hh.exe spawning suspicious child processes, including shell utilities and other native Windows utilities
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Stealth | T1218.001 System Binary Proxy Execution: Compiled HTML File |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Sysmon | Event ID 1 | Process creation |
Rule body yaml
id: '17798.30045'
title: Suspicious Child Process for hh.exe
description: 'Adversaries may abuse Compiled HTML files (.chm) to conceal malicious
code. CHM files are commonly distributed as part of the Microsoft HTML Help system.
A custom CHM file containing embedded payloads could be delivered to a victim then
triggered by User Execution. This use case detects hh.exe spawning suspicious child
processes, including shell utilities and other native Windows utilities. -- Threat
Actor Association: APT-K-47/Mysterious Elephant -- LOLBAS Atomics T1218.001 Test
#2'
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<")
(TERM(hh) OR "hh.exe") (TERM(cmd) OR TERM(powershell) OR TERM(pwsh) OR TERM(wscript)
OR TERM(cscript) OR TERM(regsvr32) OR TERM(wmic) OR TERM(rundll32) OR TERM(MSHTA)
OR TERM(CertUtil) OR TERM(CertReq) OR TERM(MSbuild) OR TERM(installutil) OR TERM(schtasks)
OR TERM(msiexec)) | where match(parent_process_name, "(?i)hh\.exe") and match(process_name,
"(?i)cmd|powershell|pwsh|wscript|cscript|regsvr32|wmic|rundll32|MSHTA|CertUtil|CertReq|MSbuild|installutil|schtasks|msiexec")
| table _time, host, user process, process_*, parent_process_* | bin span=1s | stats
values(*) as * by _time, host '
techniques:
- defense-evasion:system binary proxy execution:compiled html file
technique_id:
- T1218.001
data_category:
- Windows Sysmon
references:
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.001/T1218.001.md#atomic-test-2---compiled-html-help-remote-payload
- https://www.ptsecurity.com/ww-en/analytics/pt-esc-threat-intelligence/higaisa-or-winnti-apt-41-backdoors-old-and-new/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<") (TERM(hh) OR "hh.exe") (TERM(cmd) OR TERM(powershell) OR TERM(pwsh) OR TERM(wscript) OR TERM(cscript) OR TERM(regsvr32) OR TERM(wmic) OR TERM(rundll32) OR TERM(MSHTA) OR TERM(CertUtil) OR TERM(CertReq) OR TERM(MSbuild) OR TERM(installutil) OR TERM(schtasks) OR TERM(msiexec))
Stage 2: where
| where match(parent_process_name, "(?i)hh\.exe") and match(process_name, "(?i)cmd|powershell|pwsh|wscript|cscript|regsvr32|wmic|rundll32|MSHTA|CertUtil|CertReq|MSbuild|installutil|schtasks|msiexec")
Stage 3: table
| table _time, host, user process, process_*, parent_process_*
Stage 4: bucket
| bin span=1s
Stage 5: stats
| stats values(*) as * by _time, host
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
EventCode | eq |
|
parent_process_name | match |
|
process_name | match |
|
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | TERM |
| 1 | "<EventID>1<" |
| 1 | TERM |
| 1 | hh |
| 1 | "hh.exe" |
| 1 | TERM |
| 1 | cmd |
| 1 | TERM |
| 1 | powershell |
| 1 | TERM |
| 1 | pwsh |
| 1 | TERM |
| 1 | wscript |
| 1 | TERM |
| 1 | cscript |
| 1 | TERM |
| 1 | regsvr32 |
| 1 | TERM |
| 1 | wmic |
| 1 | TERM |
| 1 | rundll32 |
| 1 | TERM |
| 1 | MSHTA |
| 1 | TERM |
| 1 | CertUtil |
| 1 | TERM |
| 1 | CertReq |
| 1 | TERM |
| 1 | MSbuild |
| 1 | TERM |
| 1 | installutil |
| 1 | TERM |
| 1 | schtasks |
| 1 | TERM |
| 1 | msiexec |