Detection rules › Splunk
rundll32.exe Executing DLL from Non-standard Directory (Sysmon)
rundll32.exe is a legitimate Windows utility used to run functions stored in Dynamic Link Libraries. Because rundll32 is a trusted system utility with the ability to execute code, it is a high value target for abuse by threat actors. Threat actors leveraging Qbot malware have been observed dropping DLLs into writeable paths and calling them with rundll32.exe. This use case detects when a DLL in a nonstandard directory is called by rundll32
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Stealth | T1218.011 System Binary Proxy Execution: Rundll32 |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Sysmon | Event ID 1 | Process creation |
Rule body yaml
id: '27238.49667'
title: rundll32.exe Executing DLL from Non-standard Directory
description: rundll32.exe is a legitimate Windows utility used to run functions stored
in Dynamic Link Libraries. Because rundll32 is a trusted system utility with the
ability to execute code, it is a high value target for abuse by threat actors. Threat
actors leveraging Qbot malware have been observed dropping DLLs into writeable paths
and calling them with rundll32.exe. This use case detects when a DLL in a nonstandard
directory is called by rundll32. Living Off the Land Binary and Scripts (LOLBAS)
(LOLBIN)
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<")
"rundll32" ".dll" | regex process_name="(?i)rundll32\.exe"| regex process!="(?i)(rundll32(\.exe)?\"?\s+(\/\w+\s+)?[\w.]+\.dll)|(C:\x5c(Windows\x5c(System32|WinSxS|SysWoW64)|Program\sFiles(\s\(x86\))?\x5c.+\.dll))"|
table _time, host, user, process_*, process, parent_process_* | bin span=1s | stats
values(*) as * by _time, host '
techniques:
- defense-evasion:system binary proxy execution:rundll32
technique_id:
- T1218.011
data_category:
- Windows Sysmon
references:
- https://redcanary.com/blog/lolbins-abuse/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_sysmon` (TERM(EventCode=1) OR "<EventID>1<") "rundll32" ".dll"
Stage 2: regex
| regex process_name="(?i)rundll32\.exe"
Stage 3: regex
| regex process!="(?i)(rundll32(\.exe)?\"?\s+(\/\w+\s+)?[\w.]+\.dll)|(C:\x5c(Windows\x5c(System32|WinSxS|SysWoW64)|Program\sFiles(\s\(x86\))?\x5c.+\.dll))"
Stage 4: table
| table _time, host, user, process_*, process, parent_process_*
Stage 5: bucket
| bin span=1s
Stage 6: stats
| stats values(*) as * by _time, host
Exclusions
Top-level NOT(...) conjuncts: predicates this rule actively suppresses.
| Field | Kind | Excluded values |
|---|---|---|
process | regex_match | "(?i)(rundll32(.exe)?\"?\s+(\/\w+\s+)?[\w.]+.dll), (C:\x5c(Windows\x5c(System32|WinSxS|SysWoW64)|Program\sFiles(\s(x86))?\x5c.+.dll))" |
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 |
|
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>1<" |
| 1 | "rundll32" |
| 1 | ".dll" |