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Upgrade to ProDetect Polymorphic Code in Sumo Logic CSE
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/
Sumo Detection Query
_sourceCategory=windows/sysmon EventCode=11
| parse regex field=_raw "TargetFilename: (?P<TargetFilename>[^\r\n]+)"
| parse regex field=_raw "Image: (?P<Image>[^\r\n]+)"
| parse regex field=_raw "SHA256: (?P<SHA256>[^\r\n]+)"
| parse regex field=_raw "Computer: (?P<Computer>[^\r\n]+)"
| where TargetFilename matches "(?i).*(\\temp\\|\\appdata\\|\\programdata\\|\\users\\public\\).*"
| where TargetFilename matches "(?i).*\.(exe|dll|scr|bin)$"
| timeslice 1h
| stats
dcount(SHA256) as UniqueHashes,
count as FilesWritten,
values(TargetFilename) as FileList
by _timeslice, Computer, Image
| where UniqueHashes >= 3
| sort by UniqueHashes desc
| fields _timeslice, Computer, Image, UniqueHashes, FilesWritten, FileListSumo Logic search over Sysmon EventCode 11 (FileCreate) events, parsing TargetFilename, Image process path, and SHA256 hash fields to identify processes writing 3 or more uniquely-hashed PE files to user-writable directories within one-hour timeslices — a hallmark of polymorphic dropper behavior.
Data Sources
Required Tables
False Positives & Tuning
- Package managers (chocolatey, winget) downloading multiple versioned packages with distinct hashes to local cache directories
- Security tools performing controlled malware analysis or sandboxing that write multiple sample variants locally
- CD/CI pipelines running on developer machines that build and test multiple binary artifacts to temp directories
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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