Windows Shell/Scripting Processes Spawning Suspicious Programs

Severity: high
Author: Florian Roth (Nextron Systems), Tim Shelton
Source: upstream

Detects suspicious child processes of a Windows shell and scripting processes such as wscript, rundll32, powershell, mshta...etc.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell, `T1059.005` Command and Scripting Interpreter: Visual Basic
Defense Evasion	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `selection`

or:
Image|endswith: '\bitsadmin.exe'
Image|endswith: '\certutil.exe'
Image|endswith: '\mshta.exe'
Image|endswith: '\nslookup.exe'
Image|endswith: '\schtasks.exe'
or:
ParentImage|endswith: '\cscript.exe'
ParentImage|endswith: '\mshta.exe'
ParentImage|endswith: '\powershell.exe'
ParentImage|endswith: '\pwsh.exe'
ParentImage|endswith: '\regsvr32.exe'
ParentImage|endswith: '\rundll32.exe'
ParentImage|endswith: '\wmiprvse.exe'
ParentImage|endswith: '\wscript.exe'

Stage 2: `not 1 of filter_*`

or:
CommandLine|contains: 'C:\MEM_Configmgr_'
CommandLine|contains: '\SMSSETUP\BIN\'
CommandLine|contains: '\autorun.hta'
CommandLine|contains: '{1E460BD7-F1C3-4B2E-88BF-4E770A288AF5}'
Image|endswith: '\mshta.exe'
ParentCommandLine|contains: 'C:\MEM_Configmgr_'
ParentCommandLine|contains: '\splash.hta'
ParentCommandLine|contains: '{1E460BD7-F1C3-4B2E-88BF-4E770A288AF5}'
ParentImage|endswith: '\mshta.exe'
CommandLine|contains: '\nessus_'
CurrentDirectory|contains: '\ccmcache\'
ParentCommandLine|contains: '\Program Files\Amazon\WorkSpacesConfig\Scripts\check-workspacehealth.ps1'
ParentCommandLine|contains: '\Program Files\Amazon\WorkSpacesConfig\Scripts\set-selfhealing.ps1'
ParentCommandLine|contains: '\Program Files\Amazon\WorkSpacesConfig\Scripts\setup-scheduledtask.ps1'
ParentCommandLine|contains: '\nessus_'

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	`C:\MEM_Configmgr_` `\SMSSETUP\BIN\` `\autorun.hta` `\nessus_` `{1E460BD7-F1C3-4B2E-88BF-4E770A288AF5}`
`CurrentDirectory`	match	`\ccmcache\`
`Image`	ends_with	`\bitsadmin.exe` corpus 23 (sigma 23) `\certutil.exe` corpus 34 (sigma 34) `\mshta.exe` corpus 57 (sigma 57) `\nslookup.exe` corpus 4 (sigma 4) `\schtasks.exe` corpus 45 (sigma 45)
`ParentCommandLine`	match	`C:\MEM_Configmgr_` `\Program Files\Amazon\WorkSpacesConfig\Scripts\check-workspacehealth.ps1` `\Program Files\Amazon\WorkSpacesConfig\Scripts\set-selfhealing.ps1` `\Program Files\Amazon\WorkSpacesConfig\Scripts\setup-scheduledtask.ps1` `\nessus_` `\splash.hta` `{1E460BD7-F1C3-4B2E-88BF-4E770A288AF5}`
`ParentImage`	ends_with	`\cscript.exe` corpus 14 (sigma 14) `\mshta.exe` corpus 10 (sigma 10) `\powershell.exe` corpus 16 (sigma 16) `\pwsh.exe` corpus 16 (sigma 16) `\regsvr32.exe` corpus 11 (sigma 11) `\rundll32.exe` corpus 12 (sigma 12) `\wmiprvse.exe` corpus 3 (sigma 3) `\wscript.exe` corpus 14 (sigma 14)