Squiblydoo

[John Wunder]

Squiblydoo

Squiblydoo is a specific usage of regsvr32.dll to load a COM scriptlet directly from the internet and execute it in a way that bypasses application whitelisting. It can be seen by looking for regsvr32.exe executions that load the scrobj.dll (which execute the COM scriptlet) or, if that is too noisy, those that also load content directly via HTTP or HTTPS.

Squiblydoo was first written up by Casey Smith at Red Canary, though that blog post is no longer accessible.

ATT&CK Coverage

Technique	Level of Coverage
Regsvr32	Low

Implementations

This looks for any and all usage of the scrobj DLL, which is what is used to run COM scriptlets, so it'll detect both loading from network as well as filesystem. This will have almost zero false positives so is suitable for alerting.

Language: Splunk
Data Model: Sysmon

index=__your_sysmon_events__ EventCode=1 regsvr32.exe scrobj.dll | search Image="*regsvr32.exe"

Test Cases

The Atomic Red Team test for Squiblydoo is a good test case for this.

Data Model Mappings

Object	Action	Field
process	create	exe
process	create	command_line

References

As usual, credit to Roberto Rodriguez and the ThreatHunter Playbook.

Developer Certificate of Origin

DCO signed-off by: John Wunder [e-mail]

[Ivan Kirillov]

Added in 3716644