Detection rules › Splunk
DLL Called with RS32 (PowerShell)
Threat actors including Qbot have been observed using rundll32.exe to invoke the RS32 function during post-compromise activity. This use case detects DLL files invoking RS32 , accounting for instances where rundll32.exe has been renamed. While these exexcutions may be legitimate, unexpected executions should be investigated
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Stealth | T1218.011 System Binary Proxy Execution: Rundll32 |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| PowerShell | Event ID 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Rule body yaml
id: '27060.49391'
title: DLL Called with RS32
description: Threat actors including Qbot have been observed using rundll32.exe to
invoke the RS32 function during post-compromise activity. This use case detects
DLL files invoking RS32 , accounting for instances where rundll32.exe has been renamed.
While these exexcutions may be legitimate, unexpected executions should be investigated.
Living Off the Land Binary and Scripts (LOLBAS) (LOLBIN)
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4104) OR
"<EventID>4104<") ".dll" "RS32" | where match(process, "(?i)\.dll\,RS32") | table
_time, host, user, process, process_*, parent_process, parent_process_*, called_function
| bin span=1s | stats values(*) as * by _time, host '
techniques:
- defense-evasion:system binary proxy execution:rundll32
technique_id:
- T1218.011
data_category:
- PowerShell logs
references:
- https://redcanary.com/blog/lolbins-abuse/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_powershell` (TERM(EventCode=4104) OR "<EventID>4104<") ".dll" "RS32"
Stage 2: where
| where match(process, "(?i)\.dll\,RS32")
Stage 3: table
| table _time, host, user, process, process_*, parent_process, parent_process_*, called_function
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>4104<" |
| 1 | ".dll" |
| 1 | "RS32" |