Chopper Webshell Process Pattern

Severity: high
Author: Florian Roth (Nextron Systems), MSTI (query)
Source: upstream

Detects patterns found in process executions cause by China Chopper like tiny (ASPX) webshells

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1505.003` Server Software Component: Web Shell
Discovery	`T1018` Remote System Discovery, `T1033` System Owner/User Discovery, `T1087` Account Discovery

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_origin`

or:
Image|endswith: '\w3wp.exe'
ParentImage|endswith: '\w3wp.exe'

Stage 2: `all of selection_cmdline`

or:
CommandLine|contains: '&c:&echo'
CommandLine|contains: '&cd&echo'
CommandLine|contains: '&dir&echo'
CommandLine|contains: '&echo [E]'
CommandLine|contains: '&echo [S]'
CommandLine|contains: '&ipconfig&echo'
CommandLine|contains: '&quser&echo'
CommandLine|contains: '&whoami&echo'

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	`&c:&echo` `&cd&echo` corpus 2 (sigma 2) `&dir&echo` `&echo [E]` `&echo [S]` `&ipconfig&echo` `&quser&echo` `&whoami&echo`
`Image`	ends_with	`\w3wp.exe` corpus 6 (sigma 6)
`ParentImage`	ends_with	`\w3wp.exe` corpus 8 (sigma 8)