Suspicious IIS Module Registration

Severity: high
Author: Florian Roth (Nextron Systems), Microsoft (idea)
Source: upstream

Detects a suspicious IIS module registration as described in Microsoft threat report on IIS backdoors

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1505.004` Server Software Component: IIS Components

Event coverage

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

Stages and Predicates

Stage 1: `selection_parent`

ParentImage|endswith: '\w3wp.exe'

Stage 2: `1 of selection_cli_1`

CommandLine|contains: 'appcmd.exe add module'

Stage 3: `1 of selection_cli_2`

CommandLine|contains: ' system.enterpriseservices.internal.publish'
Image|endswith: '\powershell.exe'

Stage 4: `1 of selection_cli_3`

CommandLine|contains: ' /I'
CommandLine|contains: gacutil

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	`/I` `system.enterpriseservices.internal.publish` `appcmd.exe add module` `gacutil`
`Image`	ends_with	`\powershell.exe` corpus 143 (sigma 143)
`ParentImage`	ends_with	`\w3wp.exe` corpus 8 (sigma 8)

Suspicious IIS Module Registration

MITRE ATT&CK coverage

Event coverage

Stages and Predicates

Stage 1: selection_parent

Stage 2: 1 of selection_cli_1

Stage 3: 1 of selection_cli_2

Stage 4: 1 of selection_cli_3

Indicators

Stage 1: `selection_parent`

Stage 2: `1 of selection_cli_1`

Stage 3: `1 of selection_cli_2`

Stage 4: `1 of selection_cli_3`