Detecting Process Hollowing Technique

Detecting Process Hollowing Technique

When to Use

• When investigating suspected fileless malware or in-memory threats
• After EDR alerts on process injection or suspicious memory operations
• When hunting for defense evasion techniques in a compromised environment
• When threat intel reports indicate process hollowing in active campaigns
• During purple team exercises validating T1055.012 detection coverage

Detection Gaps & Validation

• Event ID 25 requires Sysmon 13+: ProcessTampering (the cleanest hollowing signal) does not exist on older agents — confirm the Sysmon version or you silently miss every hollowing event. EID 25 also only flags image/section divergence, not all RunPE variants.
• CREATE_SUSPENDED is not logged directly: the suspended-create → unmap → write → resume chain has no single event. Stitch EID 1 (process create) + EID 8 (CreateRemoteThread) + EID 10 (ProcessAccess 0x0008 PROCESS_VM_OPERATION / 0x0020 PROCESS_VM_WRITE) on the same target PID.
• Image-mismatch hunting: compare Sysmon EID 7 (ImageLoaded) OriginalFileName/hash against the on-disk path; a svchost.exe with no services.exe parent (EID 1 ParentImage) and outbound EID 3 is a strong tell.
• Evasions: process doppelgänging (T1055.013, NTFS transactions) and process ghosting bypass EID 25; module stomping reuses a legit DLL's memory so ImageLoaded looks clean — fall back to pe-sieve, Hollows Hunter, or Moneta memory scans.
• Validate: run Atomic Red Team T1055.012 (or a known RunPE PoC) and confirm EID 25 plus the EID 8/10 correlation fire in the SIEM.
• Tune FPs: debuggers, AV/EDR, and installers legitimately write cross-process memory — exclude by signed SourceImage and known RMM/security tooling, not by target name.

Prerequisites

• EDR with memory protection monitoring (CrowdStrike, MDE, SentinelOne)
• Sysmon with Event IDs 1 (Process Create), 8 (CreateRemoteThread), 25 (ProcessTampering)
• Windows ETW providers for process hollowing (Microsoft-Windows-Kernel-Process)
• Memory forensics capabilities (Volatility, WinDbg)
• Process integrity monitoring tools

Workflow

1. Understand Hollowing Mechanics: Process hollowing involves creating a legitimate process in suspended state, unmapping its memory, writing malicious code, then resuming execution.
2. Monitor Suspended Process Creation: Hunt for processes created with CREATE_SUSPENDED flag followed by memory writes and thread resumption.
3. Detect Memory Section Anomalies: Identify processes where the in-memory image differs from the on-disk binary (image mismatch).
4. Analyze Parent-Child Process Trees: Flag processes whose behavior does not match their binary name (e.g., svchost.exe making unusual network connections).
5. Check Process Integrity: Compare process memory sections against the legitimate binary on disk.
6. Correlate with Network Activity: Hollowed processes often establish C2 connections - correlate suspicious process behavior with network logs.
7. Document and Contain: Report findings, isolate affected endpoints, and update detection rules.

Key Concepts

Tools & Systems

Common Scenarios

1. Svchost.exe Hollowing: Malware creates svchost.exe suspended, hollows it, injects backdoor code - process appears legitimate but behaves maliciously.
2. Explorer.exe Hollowing: Attacker hollows explorer.exe to inherit its network permissions and trusted process context.
3. Rundll32 Hollowing: Malicious loader creates rundll32.exe, replaces its memory with implant code for C2 beaconing.
4. Multi-Stage Hollowing: Loader uses process hollowing as first stage, then performs additional injection into services.

Output Format

Hunt ID: TH-HOLLOW-[DATE]-[SEQ]
Technique: T1055.012
Hollowed Process: [Process name and PID]
Original Binary: [Expected on-disk path]
Parent Process: [Parent name and PID]
Memory Mismatch: [Yes/No]
Suspicious APIs: [NtUnmapViewOfSection, WriteProcessMemory, etc.]
Network Activity: [C2 connections if any]
Host: [Hostname]
User: [Account context]
Risk Level: [Critical/High/Medium/Low]