Suspicious MSHTA Child Process

Severity: high
Author: Michael Haag
Source: upstream

Detects a suspicious process spawning from an "mshta.exe" process, which could be indicative of a malicious HTA script execution

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218.005` System Binary Proxy Execution: Mshta

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_parent`

ParentImage|endswith: '\mshta.exe'

Stage 2: `all of selection_child`

or:
Image|endswith: '\bash.exe'
Image|endswith: '\bitsadmin.exe'
Image|endswith: '\cmd.exe'
Image|endswith: '\cscript.exe'
Image|endswith: '\powershell.exe'
Image|endswith: '\pwsh.exe'
Image|endswith: '\reg.exe'
Image|endswith: '\regsvr32.exe'
Image|endswith: '\sh.exe'
Image|endswith: '\wscript.exe'
OriginalFileName: Bash.exe
OriginalFileName: Cmd.Exe
OriginalFileName: PowerShell.EXE
OriginalFileName: REGSVR32.EXE
OriginalFileName: bitsadmin.exe
OriginalFileName: cscript.exe
OriginalFileName: pwsh.dll
OriginalFileName: reg.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	`\bash.exe` corpus 17 (sigma 17) `\bitsadmin.exe` corpus 23 (sigma 23) `\cmd.exe` corpus 92 (sigma 92) `\cscript.exe` corpus 64 (sigma 64) `\powershell.exe` corpus 143 (sigma 143) `\pwsh.exe` corpus 140 (sigma 140) `\reg.exe` corpus 46 (sigma 46) `\regsvr32.exe` corpus 57 (sigma 57) `\sh.exe` corpus 13 (sigma 13) `\wscript.exe` corpus 64 (sigma 64)
`OriginalFileName`	eq	`Bash.exe` corpus 3 (sigma 3) `Cmd.Exe` corpus 32 (sigma 30, splunk 2) `PowerShell.EXE` corpus 64 (sigma 60, splunk 4) `REGSVR32.EXE` corpus 10 (sigma 10) `bitsadmin.exe` corpus 9 (sigma 9) `cscript.exe` corpus 15 (sigma 15) `pwsh.dll` corpus 72 (sigma 68, splunk 4) `reg.exe` corpus 29 (sigma 29) `wscript.exe` corpus 15 (sigma 15)
`ParentImage`	ends_with	`\mshta.exe` corpus 10 (sigma 10)