Detection rules › Splunk
Certutil Obfuscate_Encode Files (PowerShell)
Certutil can be used to encode files to evade defensive measures
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Stealth | T1027 Obfuscated Files or Information |
| Command & Control | T1132 Data Encoding |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| PowerShell | Event ID 4103 | Payload Context: ContextInfo User Data: UserData. |
| PowerShell | Event ID 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Rule body yaml
id: '6158.6686'
title: Certutil Obfuscate_Encode Files
description: 'Certutil can be used to encode files to evade defensive measures. --
Threat Actor Association: APT29/Nobelium/Cozy Bear, Arid Viper/APT C-23, BlackTech
- Software Association: Conti'
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4104) OR
"<EventID>4104<" OR TERM(EventCode=4103) OR "<EventID>4103<") "certutil" TERM(encode)
| table _time, host, user, signature_id, process | bin span=1s | stats values(*)
as * by _time, host '
techniques:
- command-and-control:data encoding
- defense-evasion:obfuscated files or information
technique_id:
- T1027
- T1132
data_category:
- PowerShell logs
- Process command-line parameters
references:
- https://lolbas-project.github.io/lolbas/Binaries/Certutil/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4104) OR "<EventID>4104<" OR TERM(EventCode=4103) OR "<EventID>4103<") "certutil" TERM(encode)
Stage 2: table
| table _time, host, user, signature_id, process
Stage 3: bucket
| bin span=1s
Stage 4: stats
| stats values(*) as * by _time, host
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 |
|---|---|---|
EventCode | eq |
|
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | TERM |
| 1 | "<EventID>4104<" |
| 1 | TERM |
| 1 | "<EventID>4103<" |
| 1 | "certutil" |
| 1 | TERM |
| 1 | encode |