System Binary Proxy Execution: Compiled HTML File T1218.001
Tactic: Stealth
Adversaries may abuse Compiled HTML files (.chm) to conceal malicious code. CHM files are commonly distributed as part of the Microsoft HTML Help system. CHM files are compressed compilations of various content such as HTML documents, images, and scripting/web related programming languages such VBA, JScript, Java, and ActiveX. CHM content is displayed using underlying components of the Internet Explorer browser loaded by the HTML Help executable program (hh.exe).
Events covered
5 catalog events are tagged with this technique by at least one rule.
| Provider | Event | Title |
|---|---|---|
| Sysmon | Event ID 1 | Process creation |
| Sysmon | Event ID 3 | Network connection |
| Security-Auditing | Event ID 4688 | A new process has been created. |
| PowerShell | Event ID 4103 | Payload Context: ContextInfo User Data: UserData. |
| PowerShell | Event ID 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Authoring guide
Patterns shared across the 22 rules above: which fields they filter on, what specific values they look for, and what they exclude. The catalog normalizes field names across vendors so Sigma's Image, Elastic's process.name, and Splunk's process_name collapse into one row. Each rule contributes at most once per row.
Fields filtered most (11 distinct)
The fields most rules look at when detecting this technique. The How column shows the operators authors use (eq, wildcard, regex_match, match) and how often each appears. Sample values are concrete examples to start from, not an exhaustive list.
Top indicator values (116 distinct)
Specific (field, operator, value) combinations the rules check for, ranked by how many rules under this technique use each one. The Corpus reach column counts how many rules across the entire catalog (any technique) check the same combination. High numbers point to widely-used indicators that are likely noisy on their own; combine them with another condition for useful signal. Blank means the combination is specific to rules under this technique. Click a value to expand the rules under this technique that use it.
Exclusions (31 distinct)
Field/operator/value combinations excluded by rules under this technique (top-level not() clauses), sorted by how many rules exclude each. These are the false-positive paths the community has learned to filter out. A new rule that ignores the high-count entries here will likely fire on the same noisy paths. Click a value to expand the rules under this technique that exclude it.
Rules under this technique
Every rule in the catalog tagged with this technique, grouped by vendor. Click a rule title for its full predicates, exclusions, and indicators.
Sigma 6 rules
- HH.EXE Execution
- HH.EXE Initiated HTTP Network Connection
- HTML Help HH.EXE Suspicious Child Process
- OneNote.EXE Execution of Malicious Embedded Scripts
- Remote CHM File Download/Execution Via HH.EXE
- Suspicious HH.EXE Execution
Elastic 3 rules
- Network Connection via Compiled HTML File
- Process Activity via Compiled HTML File
- Suspicious MS Office Child Process
Splunk 13 rules
- Detect HTML Help Renamed
- Detect HTML Help Spawn Child Process
- Detect HTML Help URL in Command Line
- Detect HTML Help Using InfoTech Storage Handlers
- hh.exe Execution (PowerShell)
- hh.exe Execution (Sysmon)
- hh.exe Execution (Windows Event Log)
- hh.exe Remote File Execution (PowerShell)
- hh.exe Remote File Execution (Sysmon)
- hh.exe Remote File Execution (Windows Event Log)
- Suspicious Child Process for hh.exe (Sysmon)
- Suspicious Child Process for hh.exe (Windows Event Log)
- Windows System Binary Proxy Execution Compiled HTML File Decompile