C# IL Code Compilation Via Ilasm.EXE

Severity: medium
Author: frack113, Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects the use of "Ilasm.EXE" in order to compile C# intermediate (IL) code to EXE or DLL.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1127` Trusted Developer Utilities Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

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

Stage 2: `all of selection_cli`

or:
CommandLine|contains: ' /dll'
CommandLine|contains: ' /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
`CommandLine`	match	`/dll` `/exe`
`Image`	ends_with	`\ilasm.exe`
`OriginalFileName`	eq	`ilasm.exe`