Detection rules › Splunk
Certutil Obfuscate_Encode Files (EDR)
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 |
|---|---|---|
| Sysmon | Event ID 1 | Process creation |
| Security-Auditing | Event ID 4688 | A new process has been created. |
Rule body yaml
id: '6158.14342'
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_edr` ((event_type IN ("childproc","netconn","proc"))
OR (TERM(ProcessRollup2) OR Type=Process) OR TERM(DeviceProcessEvents)) ("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") `hec_collect`'
techniques:
- command-and-control:data encoding
- defense-evasion:obfuscated files or information
technique_id:
- T1027
- T1132
data_category:
- Process command-line parameters
- EDR Logs
references:
- https://lolbas-project.github.io/lolbas/Binaries/Certutil/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_edr` ((event_type IN ("childproc","netconn","proc")) OR (TERM(ProcessRollup2) OR Type=Process) OR TERM(DeviceProcessEvents)) ("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") `hec_collect`
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 |
|---|---|---|
event_type | in |
|
process | match |
|
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 | ProcessRollup2 |
| 1 | TERM |
| 1 | DeviceProcessEvents |
| 1 | "certutil" |
| 1 | "-encode" |
| 1 | "-encodehex" |
| 1 | "-encode" |
| 1 | "-encodehex" |