Suspicious File Downloaded From Direct IP Via Certutil.EXE

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

Detects the execution of certutil with certain flags that allow the utility to download files from direct IPs.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1027` Obfuscated Files or Information
Command & Control	`T1105` Ingress Tool Transfer

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\certutil.exe'
OriginalFileName: CertUtil.exe

Stage 2: `all of selection_flags`

or:
CommandLine|contains: 'URL '
CommandLine|contains: 'urlcache '
CommandLine|contains: 'verifyctl '

Stage 3: `all of selection_http`

or:
CommandLine|contains: '://1'
CommandLine|contains: '://2'
CommandLine|contains: '://3'
CommandLine|contains: '://4'
CommandLine|contains: '://5'
CommandLine|contains: '://6'
CommandLine|contains: '://7'
CommandLine|contains: '://8'
CommandLine|contains: '://9'

Stage 4: `not 1 of filter_main_seven_zip`

CommandLine|contains: '://7-'

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	`://1` corpus 3 (sigma 3) `://2` corpus 3 (sigma 3) `://3` corpus 3 (sigma 3) `://4` corpus 3 (sigma 3) `://5` corpus 3 (sigma 3) `://6` corpus 3 (sigma 3) `://7` corpus 3 (sigma 3) `://7-` corpus 2 (sigma 2) `://8` corpus 3 (sigma 3) `://9` corpus 3 (sigma 3) `URL` corpus 3 (sigma 3) `urlcache` corpus 3 (sigma 3) `verifyctl` corpus 3 (sigma 3)
`Image`	ends_with	`\certutil.exe` corpus 34 (sigma 34)
`OriginalFileName`	eq	`CertUtil.exe` corpus 13 (sigma 13)

Suspicious File Downloaded From Direct IP Via Certutil.EXE

MITRE ATT&CK coverage

Event coverage

Stages and Predicates

Stage 1: all of selection_img

Stage 2: all of selection_flags

Stage 3: all of selection_http

Stage 4: not 1 of filter_main_seven_zip

Indicators

Stage 1: `all of selection_img`

Stage 2: `all of selection_flags`

Stage 3: `all of selection_http`

Stage 4: `not 1 of filter_main_seven_zip`