Detect Dynamic API Resolution in Microsoft Sentinel
Adversaries may obfuscate then dynamically resolve API functions called by their malware in order to conceal malicious functionalities and impair defensive analysis. API functions called by malware leave static artifacts such as strings in payload files and in the Import Address Table (IAT). To avoid static analysis, adversaries use dynamic API resolution: hashes of function names are stored in malware in lieu of literal strings, and malware uses GetProcAddress() and LoadLibrary() to manually reproduce the linking process. Threat actors including Mustang Panda, Lazarus Group, Latrodectus, Bazar, Brute Ratel C4, TONESHELL, PlugX, Raccoon Stealer, AvosLocker, and CHIMNEYSWEEP use this technique.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1027 Obfuscated Files or Information
- Sub-technique
- T1027.007 Dynamic API Resolution
- Canonical reference
- https://attack.mitre.org/techniques/T1027/007/
KQL Detection Query
DeviceImageLoadEvents
| where Timestamp > ago(24h)
| where FileName in~ ("kernel32.dll", "ntdll.dll", "kernelbase.dll")
| where not (InitiatingProcessFolderPath startswith "C:\\Windows\\"
or InitiatingProcessFolderPath startswith "C:\\Program Files\\"
or InitiatingProcessFolderPath startswith "C:\\Program Files (x86)\\")
| summarize
LoadedModules=make_set(FileName),
ModuleCount=dcount(FileName),
TotalLoads=count()
by DeviceName, InitiatingProcessFileName, InitiatingProcessFolderPath, InitiatingProcessSHA256
| where ModuleCount >= 1
| join kind=leftouter (
DeviceProcessEvents
| where Timestamp > ago(24h)
| where FileName !in~ ("svchost.exe", "lsass.exe", "services.exe", "explorer.exe")
| summarize ImportCount=dcount(FileName) by DeviceName, SHA256
) on DeviceName
| project DeviceName, InitiatingProcessFileName, InitiatingProcessFolderPath,
InitiatingProcessSHA256, LoadedModules, ModuleCount
| sort by ModuleCount ascDetects processes loading kernel32.dll and ntdll.dll from non-standard directories — malware using dynamic API resolution typically has a minimal or empty IAT and loads these core libraries explicitly via LoadLibrary at runtime. The key indicator is executables from user-writable paths loading these fundamental Windows libraries with very few other DLL loads. Legitimate software from trusted locations rarely appears with this anomalous load pattern.
Data Sources
Required Tables
False Positives & Tuning
- Small portable utilities that genuinely have minimal imports and only use LoadLibrary/GetProcAddress for cross-version compatibility
- Legitimate security tools and EDR agents that use dynamic loading for compatibility across Windows versions
- Custom in-house applications written to be compatible with multiple Windows versions using dynamic API loading
- Certain Go or Rust compiled binaries that have unusual DLL load patterns compared to C/C++ equivalents
Other platforms for T1027.007
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 1Demonstrate GetProcAddress Dynamic API Resolution in PowerShell
Expected signal: Sysmon Event ID 1: PowerShell process creation with Add-Type and DllImport. PowerShell ScriptBlock Log Event ID 4104: the P/Invoke declarations and GetProcAddress call. Sysmon Event ID 7: user32.dll loaded by powershell.exe.
- Test 2API Hash Resolution Simulation
Expected signal: PowerShell ScriptBlock Log Event ID 4104: the hash function implementation and the list of API names being hashed. The output shows API-to-hash mappings as adversarial malware would store them.
- Test 3Inspect Binary IAT for Dynamic Resolution Indicators
Expected signal: Sysmon Event ID 1: dumpbin.exe execution with /imports argument on calc.exe. The findstr filter shows LoadLibrary and GetProcAddress imports if present.
- Test 4Create Minimal-Import Executable for Testing
Expected signal: Sysmon Event ID 1: csc.exe compilation (T1027.004 indicator). Sysmon Event ID 1: dynapi.exe execution from Temp. Sysmon Event ID 7: kernel32.dll and user32.dll loaded by dynapi.exe. The dynapi.exe IAT will contain only LoadLibrary and GetProcAddress.
References (5)
- https://attack.mitre.org/techniques/T1027/007/
- https://www.huntress.com/blog/hackers-no-hashing-randomizing-api-hashes-to-evade-cobalt-strike-shellcode-detection
- https://www.blackhat.com/docs/us-15/materials/us-15-Choi-API-Deobfuscator-Resolving-Obfuscated-API-Functions-In-Modern-Packers.pdf
- https://www.ired.team/offensive-security/defense-evasion/windows-api-hashing-in-malware
- https://dr4k0nia.github.io/dotnet/coding/2022/08/10/HInvoke-and-avoiding-PInvoke.html
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