Potentially Suspicious Child Processes Spawned by ConHost

Severity: high
Author: Swachchhanda Shrawan Poudel (Nextron Systems)
Source: upstream

Detects suspicious child processes related to Windows Shell utilities spawned by conhost.exe, which could indicate malicious activity using trusted system components.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1202` Indirect Command Execution, `T1218` System Binary Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_parent`

ParentImage|endswith: '\conhost.exe'

Stage 2: `all of selection_child`

or:
Image|endswith: '\cmd.exe'
Image|endswith: '\cscript.exe'
Image|endswith: '\mshta.exe'
Image|endswith: '\powershell.exe'
Image|endswith: '\powershell_ise.exe'
Image|endswith: '\pwsh.exe'
Image|endswith: '\regsvr32.exe'
Image|endswith: '\wscript.exe'
OriginalFileName: cmd.exe
OriginalFileName: cscript.exe
OriginalFileName: mshta.exe
OriginalFileName: powershell.exe
OriginalFileName: powershell_ise.exe
OriginalFileName: pwsh.dll
OriginalFileName: regsvr32.exe
OriginalFileName: wscript.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
`Image`	ends_with	`\cmd.exe` corpus 92 (sigma 92) `\cscript.exe` corpus 64 (sigma 64) `\mshta.exe` corpus 57 (sigma 57) `\powershell.exe` corpus 143 (sigma 143) `\powershell_ise.exe` corpus 27 (sigma 27) `\pwsh.exe` corpus 140 (sigma 140) `\regsvr32.exe` corpus 57 (sigma 57) `\wscript.exe` corpus 64 (sigma 64)
`OriginalFileName`	eq	`cmd.exe` corpus 3 (sigma 3) `cscript.exe` corpus 15 (sigma 15) `mshta.exe` corpus 6 (sigma 6) `powershell.exe` corpus 8 (sigma 8) `powershell_ise.exe` corpus 6 (sigma 6) `pwsh.dll` corpus 72 (sigma 68, splunk 4) `regsvr32.exe` corpus 4 (sigma 4) `wscript.exe` corpus 15 (sigma 15)
`ParentImage`	ends_with	`\conhost.exe` corpus 2 (sigma 2)