Detect Regsvr32 in Splunk
Adversaries may abuse Regsvr32.exe to proxy execution of malicious code. Regsvr32.exe is a command-line program used to register and unregister object linking and embedding controls, including DLLs, on Windows systems. The 'Squiblydoo' variation passes a URL to a remote COM scriptlet file (SCT) that executes without registry changes, making no persistent artifacts. This technique is widely used by QakBot, Emotet, Dridex, Valak, Astaroth, TA551, and many APTs including APT32, APT29, Kimsuky, Cobalt Group, Leviathan, and Storm-0501. It is one of the most abused LOLBins in the threat landscape.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1218 System Binary Proxy Execution
- Sub-technique
- T1218.010 Regsvr32
- Canonical reference
- https://attack.mitre.org/techniques/T1218/010/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
(Image="*\\regsvr32.exe" OR ParentImage="*\\regsvr32.exe")
| eval RemoteSCT=if(match(CommandLine, "http[s]?://"), 1, 0)
| eval ScrObj=if(match(CommandLine, "scrobj"), 1, 0)
| eval Unregister=if(match(CommandLine, "(/u|/unregister)"), 1, 0)
| eval SuspiciousPath=if(match(CommandLine, "(Temp|AppData|Downloads|Public|Desktop|ProgramData)"), 1, 0)
| eval InlineScript=if(match(CommandLine, "/i:"), 1, 0)
| eval OfficeParent=if(match(ParentImage, "(winword|excel|outlook|powerpnt)\.exe"), 1, 0)
| eval ScriptParent=if(match(ParentImage, "(cmd|powershell|wscript|cscript|mshta)\.exe"), 1, 0)
| eval SuspiciousChild=if(ParentImage="*\\regsvr32.exe" AND match(Image, "(cmd|powershell|wscript|cscript|rundll32|net|certutil)\.exe"), 1, 0)
| eval RiskScore=RemoteSCT + ScrObj + (SuspiciousPath * (OfficeParent + ScriptParent)) + InlineScript + OfficeParent + SuspiciousChild
| where RiskScore > 0 OR SuspiciousChild=1
| table _time, host, User, Image, CommandLine, ParentImage, ParentCommandLine, RemoteSCT, ScrObj, Unregister, SuspiciousPath, InlineScript, OfficeParent, ScriptParent, SuspiciousChild, RiskScore
| sort - _timeDetects Regsvr32 abuse using Sysmon Event ID 1 with comprehensive scoring. Squiblydoo (remote SCT) and scrobj.dll patterns score immediately. Suspicious path only scores when combined with an Office or scripting parent, reducing false positives from legitimate installers. Child process creation from regsvr32 is unconditionally flagged.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate software installers that use regsvr32.exe to register DLLs and OCX files from Program Files directories
- Windows Update and software deployment tools that register COM components via regsvr32.exe
- Third-party software (printer drivers, codecs, ActiveX controls) that register DLLs via regsvr32.exe during installation
- Enterprise software with custom COM components that are registered via automated deployment scripts
Other platforms for T1218.010
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Squiblydoo - Regsvr32 Remote SCT Execution
Expected signal: Sysmon Event ID 1: regsvr32.exe with /s /n /u /i: URL and scrobj.dll in command line. Sysmon Event ID 3: network connection attempt to 127.0.0.1:8080. Security Event ID 4688. Sysmon Event ID 7: scrobj.dll loaded by regsvr32.exe.
- Test 2Regsvr32 DLL Execution from Temp Directory
Expected signal: Sysmon Event ID 11: DLL written to Temp. Sysmon Event ID 1: regsvr32.exe with /s and Temp path. Sysmon Event ID 7: DLL loaded by regsvr32.exe. Security Event ID 4688.
- Test 3Regsvr32 Launched from PowerShell Parent
Expected signal: Sysmon Event ID 1: powershell.exe then regsvr32.exe with ParentImage=powershell.exe. SuspiciousParent fires. Security Event ID 4688 for both. Regsvr32 will fail (no valid DLL) but the process creation event fires.
References (6)
- https://attack.mitre.org/techniques/T1218/010/
- https://lolbas-project.github.io/lolbas/Binaries/Regsvr32/
- https://www.carbonblack.com/2016/04/28/threat-advisory-squiblydoo-continues-trend-of-attackers-using-native-os-tools-to-live-off-the-land/
- https://www.fireeye.com/blog/threat-research/2017/02/spear_phishing_techn.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.010/T1218.010.md
- https://support.microsoft.com/en-us/kb/249873
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