DLL Called with RS32 (Windows Event Log)

Group by: _time, host
Source: github.com/anvilogic-forge/armory

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

https://redcanary.com/blog/lolbins-abuse/

Telemetry coverage

Provider	Record / event type
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

id: '27060.49388'
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_winevent` (TERM(EventCode=4688) OR
  "<EventID>4688<" OR Type=Process) ".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:
- Process command-line parameters
- Windows event logs
references:
- https://redcanary.com/blog/lolbins-abuse/

Stages and Predicates

Stage 1: `search`

`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR "<EventID>4688<" OR Type=Process) ".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

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`EventCode`	eq	`4688` corpus 317 (splunk 283, kusto 33, elastic 1)	`field:"EventID" kind:eq value:"4688"`
`process`	regex_match	`"(?i).dll\,RS32"` corpus 3 (splunk 3)	`field:"CommandLine" kind:regex_match`

Search terms

These SPL tokens match against raw event text.

Stage	Term
1	`"<EventID>4688<"`
1	`".dll"`
1	`"RS32"`