Remote CHM File Download/Execution Via HH.EXE

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects the usage of "hh.exe" to execute/download remotely hosted ".chm" files.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218.001` System Binary Proxy Execution: Compiled HTML File

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_cli`

or:
CommandLine|contains: '\\\\'
CommandLine|contains: 'http://'
CommandLine|contains: 'https://'

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	`\\\\` corpus 7 (sigma 7) `http://` corpus 15 (sigma 15) `https://` corpus 14 (sigma 14)
`Image`	ends_with	`\hh.exe` corpus 14 (sigma 14)
`OriginalFileName`	eq	`HH.exe` corpus 5 (sigma 5)