Detect Fileless Storage in Splunk
Adversaries may store data in fileless formats to conceal malicious activity from defenses. Fileless storage includes the Windows Registry, event logs, WMI repository, and on Linux, shared memory directories (/dev/shm, /run/shm) and volatile paths (/tmp). Windows Registry-based storage is widely used by malware including QakBot, ComRAT, ShadowPad, DarkWatchman, Turla, APT32, and Volgmer to store encrypted configurations, payloads, and C2 data. Linux malware including FritzFrog (FrogShell), Muhstik, and others abuse /dev/shm and /run/shm to store binaries that are executed directly from shared memory without writing to persistent disk storage.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1027 Obfuscated Files or Information
- Sub-technique
- T1027.011 Fileless Storage
- Canonical reference
- https://attack.mitre.org/techniques/T1027/011/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=13
| eval DataLength=len(Details)
| eval IsPEInRegistry=if(match(Details, "(4D5A|MZ|TVqQ)"), 1, 0)
| eval IsLargeBase64=if(DataLength > 5000 AND match(Details, "^[A-Za-z0-9+/=]+$"), 1, 0)
| eval IsSuspiciousKey=if(match(lower(TargetObject),
"(shellcompat|printconfig|microsoft\\\\drm|applicationcontainer|\\\\plus$|gameconfiguration|scconfig)"), 1, 0)
| where IsPEInRegistry=1 OR IsLargeBase64=1 OR IsSuspiciousKey=1
| table _time, host, User, TargetObject, Details, Image, DataLength,
IsPEInRegistry, IsLargeBase64, IsSuspiciousKey
| sort - DataLength
| append [
search index=syslog host=*linux* OR index=osquery
| where match(cmdline, "(/dev/shm|/run/shm|/tmp/\.)|exec.*memfd")
| where NOT match(cmdline, "(python|java|node|ruby)")
| table _time, host, user, cmdline
]Detects fileless storage in Windows Registry (Sysmon Event ID 13 - Registry Value Set) by identifying PE magic bytes, large Base64 blobs, and known malicious registry key paths used by specific malware families. The appended search catches Linux fileless storage: execution from /dev/shm, /run/shm, and memfd (anonymous memory file descriptor) — the Linux fileless execution methods used by FritzFrog, Muhstik, and container escape malware.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate enterprise software with large registry-stored configuration blobs (some DRM systems store activation data)
- Group Policy Object (GPO) policies stored as Base64 in the registry
- Python, Java, or Node.js applications that use /dev/shm for inter-process communication (excluded in SPL)
- Database engines (PostgreSQL, Redis) using shared memory for legitimate IPC
Other platforms for T1027.011
Testing Methodology
Validate this detection against 4 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 1Store Base64-Encoded Payload in Registry (QakBot/Sibot Pattern)
Expected signal: Sysmon Event ID 12 (Registry Key Creation): new key under HKCU\Software\Microsoft. Sysmon Event ID 13 (Registry Value Set): Config value with Base64 data. PowerShell ScriptBlock Log Event ID 4104: New-ItemProperty command with Base64 value.
- Test 2Store Encrypted Configuration in Non-Standard Registry Path
Expected signal: Sysmon Event ID 12/13: registry key and value creation at HKCU\Software\ApplicationContainer\Appsw64. The Appsw64 key path matches Valak malware's known storage location. Process creation for reg.exe.
- Test 3Execute Binary from Linux Shared Memory (/dev/shm)
Expected signal: Process creation events for cp, chmod, and /dev/shm/fileless_test. Auditd execve records showing execution from /dev/shm path. Process listing would show exe=/dev/shm/fileless_test for the running process.
- Test 4WMI-Based Fileless Storage (Event Subscription)
Expected signal: Sysmon Event ID 19 (WMI Event Filter Activity): new filter created. WMI provider host (WmiPrvSE.exe) activity. The filter is stored in the WMI repository database, not as a file.
References (5)
- https://attack.mitre.org/techniques/T1027/011/
- https://learn.microsoft.com/microsoft-365/security/intelligence/fileless-threats
- https://securelist.com/a-new-secret-stash-for-fileless-malware/106393/
- https://www.elastic.co/guide/en/security/7.17/prebuilt-rule-7-16-3-binary-executed-from-shared-memory-directory.html
- https://www.akamai.com/blog/security-research/fritzfrog-botnet-new-capabilities-log4shell
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