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Upgrade to ProDetect Polymorphic Code in Elastic Security
This detection identifies behaviors associated with polymorphic or metamorphic malware that mutates its code or binary footprint at runtime to evade signature-based defenses. Because the binary hash changes with each execution, detections focus on behavioral indicators rather than static signatures: repeated file writes of executables with changing hashes, use of known mutation/packing engines, self-modifying process memory patterns, abnormal entropy in dropped files, and processes that write then immediately execute new PE files from temporary or user-writable directories. Correlation of these behaviors — especially when combined with Command and Scripting Interpreter activity or injection patterns — provides high-confidence indicators of polymorphic malware activity.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1027 Obfuscated Files or Information
- Sub-technique
- T1027.014 Polymorphic Code
- Canonical reference
- https://attack.mitre.org/techniques/T1027/014/
Elastic Detection Query
sequence by host.name, process.entity_id with maxspan=30m
[file where event.action in ("creation", "overwrite")
and file.extension in ("exe", "dll", "scr", "bin")
and file.path like~ "*\\temp\\*" or file.path like~ "*\\appdata\\*" or file.path like~ "*\\programdata\\*" or file.path like~ "*\\users\\public\\*"] with runs=3
[process where event.action == "start"
and (process.executable like~ "*\\temp\\*" or process.executable like~ "*\\appdata\\*" or process.executable like~ "*\\programdata\\*")
and not process.code_signature.trusted == true]Elastic EQL sequence rule that detects a process creating or overwriting at least 3 PE files in writable directories within 30 minutes, followed by execution of a new process from one of those directories that lacks a trusted code signature — a behavioral pattern consistent with polymorphic dropper activity.
Data Sources
Required Tables
False Positives & Tuning
- Unsigned internal tooling deployed via automation scripts to local temp directories
- Developers running locally compiled unsigned executables from AppData build output directories
- Electron app auto-updaters that extract and execute unsigned intermediate binaries during patch application
Other platforms for T1027.014
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 1Simulate Polymorphic PE Mutation via XOR Re-encoding
Expected signal: DeviceFileEvents: 5 FileCreated events in %TEMP% with distinct SHA256 hashes, all with InitiatingProcessFileName=powershell.exe. Sysmon EventID 11 entries for each variant_N.bin file.
- Test 2Drop and Execute Multiple Renamed Copies of a Binary (Hash-Change via Append)
Expected signal: DeviceFileEvents: 4 FileCreated events for svc_update_N.exe in %TEMP% with distinct SHA256 hashes. DeviceProcessEvents: 4 ProcessCreate events for svc_update_N.exe running from %TEMP% with parent cmd.exe. Sysmon EventID 11 and 1 for each iteration.
- Test 3BendyBear-Style In-Memory Stub via PowerShell Reflection (Simulation)
Expected signal: DeviceProcessEvents: PowerShell process with unusual memory allocation patterns. If Defender for Endpoint AMSI/behavior monitoring is enabled: alerts on VirtualAlloc+VirtualProtect RW->RX page permission flip from powershell.exe. Process creation event for powershell.exe with -ExecutionPolicy Bypass flag.
References (5)
- https://attack.mitre.org/techniques/T1027/014/
- https://www.sentinelone.com/cybersecurity-101/polymorphic-malware/
- https://unit42.paloaltonetworks.com/bendybear/
- https://www.linkedin.com/pulse/polymorphic-malware-how-it-works-detection-evasion-/
- https://medium.com/@understanding-polymorphic-code-in-malware
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