Findstr Launching .lnk File

Severity: medium
Author: Trent Liffick
Source: upstream

Detects usage of findstr to identify and execute a lnk file as seen within the HHS redirect attack

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1027.003` Obfuscated Files or Information: Steganography, `T1036` Masquerading, `T1202` Indirect Command Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\find.exe'
Image|endswith: '\findstr.exe'
OriginalFileName: FIND.EXE
OriginalFileName: FINDSTR.EXE

Stage 2: `all of selection_cli`

or:
CommandLine|endswith: .lnk
CommandLine|endswith: '.lnk'''
CommandLine|endswith: '.lnk"'

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`	ends_with	`.lnk` `.lnk"` `.lnk'`
`Image`	ends_with	`\find.exe` corpus 8 (sigma 8) `\findstr.exe` corpus 11 (sigma 11)
`OriginalFileName`	eq	`FIND.EXE` corpus 6 (sigma 6) `FINDSTR.EXE` corpus 10 (sigma 10)