Process Proxy Execution 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" binary to execute arbitrary processes. 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_exec`

or:
CommandLine|contains: --createShortcut
CommandLine|contains: --processStart
CommandLine|contains: --processStartAndWait

Stage 3: `not 1 of filter_optional_*`

or:
or:
CommandLine|contains: --createShortcut
CommandLine|contains: --processStart
CommandLine|contains: ':\Users\'
CommandLine|contains: Discord.exe
CommandLine|contains: '\AppData\Local\Discord\Update.exe'
or:
CommandLine|contains: --createShortcut
CommandLine|contains: --processStart
CommandLine|contains: ':\Users\'
CommandLine|contains: Teams.exe
CommandLine|contains: '\AppData\Local\Microsoft\Teams\Update.exe'
or:
CommandLine|contains: --createShortcut
CommandLine|contains: --processStart
CommandLine|contains: ':\Users\'
CommandLine|contains: Yammer.exe
CommandLine|contains: '\AppData\Local\yammerdesktop\Update.exe'
or:
CommandLine|contains: --createShortcut
CommandLine|contains: --processStartAndWait
CommandLine|contains: ':\Users\'
CommandLine|contains: GitHubDesktop.exe
CommandLine|contains: '\AppData\Local\GitHubDesktop\Update.exe'

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	`--createShortcut` `--processStart` `--processStartAndWait` `:\Users\` corpus 6 (sigma 6) `Discord.exe` `GitHubDesktop.exe` `Teams.exe` `Yammer.exe` `\AppData\Local\Discord\Update.exe` `\AppData\Local\GitHubDesktop\Update.exe` `\AppData\Local\Microsoft\Teams\Update.exe` `\AppData\Local\yammerdesktop\Update.exe`
`Image`	ends_with	`\squirrel.exe` corpus 2 (sigma 2) `\update.exe` corpus 2 (sigma 2)