Arbitrary DLL or Csproj Code Execution Via Dotnet.EXE

Severity: medium
Author: Beyu Denis, oscd.community
Source: upstream

Detects execution of arbitrary DLLs or unsigned code via a ".csproj" files via Dotnet.EXE.

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: '\dotnet.exe'
OriginalFileName: '.NET Host'

Stage 2: `all of selection_cli`

or:
CommandLine|endswith: .csproj
CommandLine|endswith: '.csproj'''
CommandLine|endswith: '.csproj"'
CommandLine|endswith: .dll
CommandLine|endswith: '.dll'''
CommandLine|endswith: '.dll"'

Stage 3: `not 1 of filter_optional_notepadplus_plus`

ParentImage: ['C:\Program Files (x86)\Notepad++\notepad++.exe', 'C:\Program Files\Notepad++\notepad++.exe']
CommandLine|contains: '-cscs_path:'
CommandLine|contains: 'C:\ProgramData\CSScriptNpp\'
CommandLine|contains: '\cs-script\cscs.dll'

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	`.csproj` `.csproj"` `.csproj'` `.dll` corpus 9 (sigma 9) `.dll"` corpus 6 (sigma 6) `.dll'` corpus 6 (sigma 6)
`CommandLine`	match	`-cscs_path:` `C:\ProgramData\CSScriptNpp\` `\cs-script\cscs.dll`
`Image`	ends_with	`\dotnet.exe` corpus 2 (sigma 2)
`OriginalFileName`	eq	`.NET Host`
`ParentImage`	eq	`C:\Program Files (x86)\Notepad++\notepad++.exe` `C:\Program Files\Notepad++\notepad++.exe`