Suspicious HH.EXE Execution

Severity: high
Author: Maxim Pavlunin
Source: upstream

Detects a suspicious execution of a Microsoft HTML Help (HH.exe)

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1566` Phishing, `T1566.001` Phishing: Spearphishing Attachment
Execution	`T1047` Windows Management Instrumentation, `T1059.001` Command and Scripting Interpreter: PowerShell, `T1059.003` Command and Scripting Interpreter: Windows Command Shell, `T1059.005` Command and Scripting Interpreter: Visual Basic, `T1059.007` Command and Scripting Interpreter: JavaScript
Defense Evasion	`T1218` System Binary Proxy Execution, `T1218.001` System Binary Proxy Execution: Compiled HTML File, `T1218.010` System Binary Proxy Execution: Regsvr32, `T1218.011` System Binary Proxy Execution: Rundll32

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\hh.exe'
OriginalFileName: HH.exe

Stage 2: `all of selection_paths`

or:
CommandLine|contains: .application
CommandLine|contains: '\AppData\Local\Temp\'
CommandLine|contains: '\Content.Outlook\'
CommandLine|contains: '\Downloads\'
CommandLine|contains: '\Users\Public\'
CommandLine|contains: '\Windows\Temp\'

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
`CommandLine`	match	`.application` `\AppData\Local\Temp\` corpus 16 (sigma 16) `\Content.Outlook\` `\Downloads\` corpus 12 (sigma 12) `\Users\Public\` corpus 17 (sigma 17) `\Windows\Temp\` corpus 10 (sigma 10)
`Image`	ends_with	`\hh.exe` corpus 14 (sigma 14)
`OriginalFileName`	eq	`HH.exe` corpus 5 (sigma 5)