Potential Suspicious Mofcomp Execution

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects execution of the "mofcomp" utility as a child of a suspicious shell or script running utility or by having a suspicious path in the commandline. The "mofcomp" utility parses a file containing MOF statements and adds the classes and class instances defined in the file to the WMI repository. Attackers abuse this utility to install malicious MOF scripts

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\mofcomp.exe'
OriginalFileName: mofcomp.exe

Stage 2: `all of selection_case`

or:
CommandLine|contains: '%appdata%'
CommandLine|contains: '%temp%'
CommandLine|contains: '%tmp%'
CommandLine|contains: '\AppData\Local\Temp'
CommandLine|contains: '\Users\Public\'
CommandLine|contains: '\WINDOWS\Temp\'
ParentImage|endswith: '\cmd.exe'
ParentImage|endswith: '\cscript.exe'
ParentImage|endswith: '\powershell.exe'
ParentImage|endswith: '\pwsh.exe'
ParentImage|endswith: '\wscript.exe'
ParentImage|endswith: '\wsl.exe'

Stage 3: `not 1 of filter_main_wmiprvse`

CommandLine|endswith: .mof
CommandLine|contains: 'C:\Windows\TEMP\'
ParentImage: 'C:\Windows\System32\wbem\WmiPrvSE.exe'

Stage 4: `not 1 of filter_optional_null_parent`

CommandLine|endswith: .mof
CommandLine|contains: 'C:\Windows\TEMP\'

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`	ends_with	`.mof`
`CommandLine`	match	`%appdata%` corpus 4 (sigma 4) `%temp%` corpus 5 (sigma 5) `%tmp%` corpus 9 (sigma 9) `C:\Windows\TEMP\` corpus 3 (sigma 3) `\AppData\Local\Temp` corpus 8 (sigma 8) `\Users\Public\` corpus 17 (sigma 17) `\WINDOWS\Temp\` corpus 2 (sigma 2)
`Image`	ends_with	`\mofcomp.exe`
`OriginalFileName`	eq	`mofcomp.exe`
`ParentImage`	ends_with	`\cmd.exe` corpus 13 (sigma 13) `\cscript.exe` corpus 14 (sigma 14) `\powershell.exe` corpus 16 (sigma 16) `\pwsh.exe` corpus 16 (sigma 16) `\wscript.exe` corpus 14 (sigma 14) `\wsl.exe` corpus 4 (sigma 4)
`ParentImage`	eq	`C:\Windows\System32\wbem\WmiPrvSE.exe`

Potential Suspicious Mofcomp Execution

MITRE ATT&CK coverage

Event coverage

Stages and Predicates

Stage 1: all of selection_img

Stage 2: all of selection_case

Stage 3: not 1 of filter_main_wmiprvse

Stage 4: not 1 of filter_optional_null_parent

Indicators

Stage 1: `all of selection_img`

Stage 2: `all of selection_case`

Stage 3: `not 1 of filter_main_wmiprvse`

Stage 4: `not 1 of filter_optional_null_parent`