Detection rules › Splunk
Bash -c Execution - Windows (Windows Event Log)
Bash is a popular default shell on Linux and macOS. Git Bash is a package that installs Bash, some common bash utilities, and Git on a Windows operating system. Bash is also included with Windows Subsystem for Linux. Bash is on the Microsoft recommended block list for executable files. This use case detects executions of bash.exe with -c.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Stealth | T1216 System Script Proxy Execution, T1218 System Binary Proxy Execution |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Security-Auditing | Event ID 4688 | A new process has been created. |
Rule body yaml
id: '33144.58774'
title: Bash -c Execution - Windows
description: Bash is a popular default shell on Linux and macOS. Git Bash is a package
that installs Bash, some common bash utilities, and Git on a Windows operating system.
Bash is also included with Windows Subsystem for Linux. Bash is on the Microsoft
recommended block list for executable files. This use case detects executions of
bash.exe with -c.
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR
"<EventID>4688<" OR Type=Process) "bash.exe" | regex process_name="(?i)bash\.exe"|
regex process="(?i)\s+-[ilsx]*c[ilsx]*" | table _time, host, user, signature_id,
process, process_*, parent_process_* | bin span=1s | stats values(*) as * by _time,
host | where event_count < 5 '
techniques:
- defense-evasion:system binary proxy execution
- defense-evasion:system script proxy execution
technique_id:
- T1218
- T1216
data_category:
- Process command-line parameters
- Windows event logs
references:
- https://lolbas-project.github.io/lolbas/Binaries/Bash/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR "<EventID>4688<" OR Type=Process) "bash.exe"
Stage 2: regex
| regex process_name="(?i)bash\.exe"
Stage 3: regex
| regex process="(?i)\s+-[ilsx]*c[ilsx]*"
Stage 4: table
| table _time, host, user, signature_id, process, process_*, parent_process_*
Stage 5: bucket
| bin span=1s
Stage 6: stats
| stats values(*) as * by _time, host
Stage 7: where
| where event_count < 5
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 |
|
event_count | lt |
|
process | regex_match |
|
process_name | regex_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 | "<EventID>4688<" |
| 1 | "bash.exe" |