Detect Process Hollowing in CrowdStrike LogScale
Adversaries may inject malicious code into suspended and hollowed processes in order to evade process-based defenses. Process hollowing is commonly performed by creating a process in a suspended state then unmapping/hollowing its memory, which can then be replaced with malicious code. A victim process can be created with native Windows API calls such as CreateProcess (which includes a flag to suspend the processes primary thread). At this point the process can be unmapped using APIs calls such as ZwUnmapViewOfSection or NtUnmapViewOfSection before being written to, realigned to the injected code, and resumed via VirtualAllocEx, WriteProcessMemory, SetThreadContext, then ResumeThread respectively. This is a widely-used technique employed by Cobalt Strike, Emotet, QakBot, and many other threat actors.
MITRE ATT&CK
- Technique
- T1055 Process Injection
- Sub-technique
- T1055.012 Process Hollowing
- Canonical reference
- https://attack.mitre.org/techniques/T1055/012/
LogScale Detection Query
#event_simpleName = "ProcessRollup2"
| FileName in ["svchost.exe", "explorer.exe", "rundll32.exe", "notepad.exe", "cmd.exe",
"mspaint.exe", "calc.exe", "dllhost.exe", "werfault.exe", "iexplore.exe",
"MSBuild.exe", "RegAsm.exe", "InstallUtil.exe", "vbc.exe", "certutil.exe"]
| not ParentBaseFileName in ["services.exe", "svchost.exe", "explorer.exe",
"winlogon.exe", "smss.exe", "csrss.exe", "wininit.exe"]
| CmdLen := length(CommandLine)
| CmdLen < 5 or CommandLine = ""
| case {
FileName = "svchost.exe" and ParentBaseFileName != "services.exe"
| HollowingIndicator := "CRITICAL - svchost.exe hollowing" ;
FileName in ["MSBuild.exe", "RegAsm.exe", "InstallUtil.exe"] and CmdLen < 10
| HollowingIndicator := "CRITICAL - .NET LOLBin hollow" ;
CmdLen < 5 or CommandLine = ""
| HollowingIndicator := "HIGH - Empty command line" ;
*
| HollowingIndicator := "MEDIUM - Unusual parent-child relationship"
}
| table([@timestamp, ComputerName, UserName, ParentBaseFileName, ParentCommandLine,
FileName, CommandLine, HollowingIndicator])
| sort(field=@timestamp, order=desc)CrowdStrike Falcon LogScale (CQL) detection for process hollowing using ProcessRollup2 endpoint telemetry events. Leverages Falcon's pre-normalized FileName and ParentBaseFileName fields (base image names without full path) to detect hollow-candidate processes launched from anomalous parent processes with near-empty command lines — consistent with the CREATE_SUSPENDED + NtUnmapViewOfSection + WriteProcessMemory + ResumeThread hollowing chain used by Cobalt Strike, Emotet, and QakBot. The CmdLen filter is computed inline before the case classification.
Data Sources
Required Tables
False Positives & Tuning
- Package management or software deployment agents (Chocolatey, WinGet wrappers) that invoke cmd.exe or certutil.exe with empty arguments under a non-standard updater parent process during silent install pre-checks
- Endpoint backup or DR recovery agents that spawn notepad.exe or calc.exe with no arguments as a live user-session canary to confirm interactive desktop presence before initiating file-level backup operations
- Some enterprise monitoring or observability agents spawn dllhost.exe or werfault.exe with minimal arguments as COM surrogate health probes from their own service process rather than from the expected svchost.exe parent
Other platforms for T1055.012
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 1Process Hollowing Detection - Anomalous svchost.exe Parent
Expected signal: Sysmon Event ID 1: svchost.exe with ParentImage=powershell.exe and empty/minimal CommandLine. This is a CRITICAL indicator — svchost.exe should only be spawned by services.exe with -k arguments.
- Test 2MSBuild.exe Hollowing Target Simulation
Expected signal: Sysmon Event ID 1: MSBuild.exe spawned by PowerShell with empty CommandLine. MSBuild.exe normally requires a project file as argument — empty execution is anomalous.
- Test 3Hollowed notepad.exe with Network Connection Check
Expected signal: Sysmon Event ID 1: notepad.exe spawned by cmd.exe. Sysmon Event ID 3: If notepad.exe makes network connections (it shouldn't normally). Security Event ID 4688 with command line auditing.
References (6)
- https://attack.mitre.org/techniques/T1055/012/
- https://new.dc414.org/wp-content/uploads/2011/01/Process-Hollowing.pdf
- https://www.endgame.com/blog/technical-blog/ten-process-injection-techniques-technical-survey-common-and-trending-process
- https://blog.nviso.eu/2020/02/04/the-return-of-the-spoof-part-2-command-line-spoofing/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1055.012/T1055.012.md
- https://www.mandiant.com/resources/staying-hidden-on-the-endpoint-evading-detection-with-shellcode
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