Detect Dynamic API Resolution in Elastic Security
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/
Elastic Detection Query
library where
dll.name in~ ("kernel32.dll", "ntdll.dll", "kernelbase.dll") and
not process.executable like~ "C:\\Windows\\*" and
not process.executable like~ "C:\\Program Files\\*" and
not process.executable like~ "C:\\Program Files (x86)\\*" and
process.executable != null and
not process.name in~ ("svchost.exe", "lsass.exe", "services.exe", "explorer.exe", "MsMpEng.exe", "SenseIR.exe", "csrss.exe")Detects dynamic API resolution (T1027.007) by identifying library load events where core Windows DLLs (kernel32.dll, ntdll.dll, kernelbase.dll) are loaded by processes residing outside standard system directories. Malware implementing hash-based API resolution calls LoadLibrary and GetProcAddress manually rather than relying on static imports, causing these DLL loads to appear from unexpected process paths such as temp directories, user home folders, or dropped locations.
Data Sources
Required Tables
False Positives & Tuning
- Portable applications (e.g., portable browsers, standalone utilities) run from user home directories or removable media that legitimately load kernel32.dll or ntdll.dll at startup
- Security tooling and debuggers (e.g., x64dbg, WinDbg, IDA Pro, Frida) installed or launched outside standard directories that instrument DLL loading for analysis purposes
- Software installers or self-extracting archives that temporarily stage and execute binaries from %TEMP% before copying to their final installation path, causing transient loads from non-standard locations
- Enterprise custom applications deployed by IT operations to non-standard directories (e.g., D:\Apps\) that legitimately import from the Windows DLL ecosystem at runtime
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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