Detection rules › Splunk
Process Creation Using Sysnative Folder (Sysmon)
Threat actors may use tools spawning processes from the Sysnative folder in an attempt to bypass the File System Redirector on 64-bit versions of Windows to execute 32-bit applications from the 64-bit system directory. This use cased detects instances where the Sysnative folder is used during process creation, a tactic often associated with CobaltStrike activities. Note: Sysnative is often referenced by legitimate processes. Allowlisting known processes is recommended to reduce false positives.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Stealth | T1218 System Binary Proxy Execution |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Sysmon | Event ID 1 | Process creation |
Rule body yaml
id: '23146.42111'
title: Process Creation Using Sysnative Folder
description: 'Threat actors may use tools spawning processes from the Sysnative folder
in an attempt to bypass the File System Redirector on 64-bit versions of Windows
to execute 32-bit applications from the 64-bit system directory. This use cased
detects instances where the Sysnative folder is used during process creation, a
tactic often associated with CobaltStrike activities. Note: Sysnative is often referenced
by legitimate processes. Allowlisting known processes is recommended to reduce false
positives.'
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<")
"Sysnative" | regex process="(?i)^[A-Z]:\x5cWindows\x5cSysnative\x5c" | table _time,
host, user, parent_process_name, process | bin span=1s | stats values(*) as * by
_time, host '
techniques:
- defense-evasion:system binary proxy execution
technique_id:
- T1218
data_category:
- Windows Sysmon
references:
- https://thedfirreport.com/2021/08/29/cobalt-strike-a-defenders-guide/
- https://learn.microsoft.com/sv-se/windows/win32/winprog64/file-system-redirector
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<") "Sysnative"
Stage 2: regex
| regex process="(?i)^[A-Z]:\x5cWindows\x5cSysnative\x5c"
Stage 3: table
| table _time, host, user, parent_process_name, process
Stage 4: bucket
| bin span=1s
Stage 5: 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.
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>1<" |
| 1 | "Sysnative" |