Arbitrary File Download Via Squirrel.EXE

Severity: medium
Author: Nasreddine Bencherchali (Nextron Systems), Karneades / Markus Neis, Jonhnathan Ribeiro, oscd.community
Source: upstream

Detects the usage of the "Squirrel.exe" to download arbitrary files. This binary is part of multiple Electron based software installations (Slack, Teams, Discord, etc.)

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\squirrel.exe'
Image|endswith: '\update.exe'

Stage 2: `all of selection_download_cli`

or:
CommandLine|contains: ' --download '
CommandLine|contains: ' --update '
CommandLine|contains: ' --updateRollback='

Stage 3: `all of selection_download_http_keyword`

CommandLine|contains: http

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	`--download` `--update` `--updateRollback=` `http` corpus 31 (sigma 31)
`Image`	ends_with	`\squirrel.exe` corpus 2 (sigma 2) `\update.exe` corpus 2 (sigma 2)