Detection rules › Splunk
Certutil Obfuscate_Encode Files (Sysmon)
Certutil can be used to encode files to evade defensive measures
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Stealth | |
| Command & Control |
References
Telemetry coverage
| Provider | Record / event type |
|---|---|
| Sysmon | Event ID 1: Process creation |
Rule body
id: '6158.23984'
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_sysmon` (TERM(EventCode=1) OR "<EventID>1<")
("certutil" (TERM(-encode) OR TERM(-encodehex))) OR (TERM(-encode) OR TERM(-encodehex))
| table _time, host, user, signature_id, process, process_*, parent_* | bin span=1s
| stats values(*) as * by _time, host | where match(process, "(?i)-encode") '
techniques:
- command-and-control:data encoding
- defense-evasion:obfuscated files or information
technique_id:
- T1027
- T1132
data_category:
- Process command-line parameters
- Windows Sysmon
references:
- https://lolbas-project.github.io/lolbas/Binaries/Certutil/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<") ("certutil" (TERM(-encode) OR TERM(-encodehex))) OR (TERM(-encode) OR TERM(-encodehex))
Stage 2: table
| table _time, host, user, signature_id, process, process_*, parent_*
Stage 3: bucket
| bin span=1s
Stage 4: stats
| stats values(*) as * by _time, host
Stage 5: where
| where match(process, "(?i)-encode")
Indicators
These rows show field, operator, and value matches.
| Field | Kind | Values | Search |
|---|---|---|---|
EventCode | eq |
| field:"EventID" kind:eq value:"1" |
process | regex_match |
| field:"CommandLine" kind:regex_match |
Search terms
These SPL tokens match against raw event text.
| Stage | Term |
|---|---|
| 1 | "<EventID>1<" |
| 1 | "certutil" |
| 1 | "-encode" |
| 1 | "-encodehex" |
| 1 | "-encode" |
| 1 | "-encodehex" |