Suspicious Child Process of AspNetCompiler

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

Detects potentially suspicious child processes of "aspnet_compiler.exe".

MITRE ATT&CK coverage

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

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `all of selection_parent`

ParentImage|endswith: '\aspnet_compiler.exe'

Stage 2: `all of selection_child`

or:
Image|endswith: '\calc.exe'
Image|endswith: '\notepad.exe'
Image|contains: ':\Temp\'
Image|contains: ':\Windows\System32\Tasks\'
Image|contains: ':\Windows\Tasks\'
Image|contains: ':\Windows\Temp\'
Image|contains: '\AppData\Local\Roaming\'
Image|contains: '\AppData\Local\Temp\'
Image|contains: '\Users\Public\'

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	`\calc.exe` corpus 13 (sigma 13) `\notepad.exe` corpus 11 (sigma 11)
`Image`	match	`:\Temp\` corpus 12 (sigma 12) `:\Windows\System32\Tasks\` corpus 4 (sigma 4) `:\Windows\Tasks\` corpus 5 (sigma 5) `:\Windows\Temp\` corpus 9 (sigma 9) `\AppData\Local\Roaming\` `\AppData\Local\Temp\` corpus 9 (sigma 9) `\Users\Public\` corpus 8 (sigma 8)
`ParentImage`	ends_with	`\aspnet_compiler.exe`