Diskshadow Script Mode - Uncommon Script Extension Execution

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

Detects execution of "Diskshadow.exe" in script mode to execute an script with a potentially uncommon extension. Initial baselining of the allowed extension list is required.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\diskshadow.exe'
OriginalFileName: diskshadow.exe

Stage 2: `all of selection_flag`

CommandLine|contains: '-s '

Stage 3: `not 1 of filter_main_ext`

CommandLine|contains: .txt

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	`-s` corpus 3 (sigma 3) `.txt` corpus 7 (sigma 7)
`Image`	ends_with	`\diskshadow.exe` corpus 3 (sigma 3)
`OriginalFileName`	eq	`diskshadow.exe` corpus 3 (sigma 3)