Detect Dynamic API Resolution in Sumo Logic CSE
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/
Sumo Detection Query
_sourceCategory=windows/sysmon EventID=7
(ImageLoaded=*kernel32.dll OR ImageLoaded=*kernelbase.dll OR ImageLoaded=*ntdll.dll)
| where !(Image matches "C:\\Windows\\*")
| where !(Image matches "C:\\Program Files\\*")
| where !(Image matches "C:\\Program Files (x86)\\*")
| where Image != ""
| count_distinct(ImageLoaded) as CoreDLLLoads, values(ImageLoaded) as LoadedLibraries by Computer, Image, ProcessGuid
| where CoreDLLLoads >= 1
| join (
_sourceCategory=windows/sysmon EventID=7
| where !(Image matches "C:\\Windows\\*")
| where !(Image matches "C:\\Program Files\\*")
| where !(Image matches "C:\\Program Files (x86)\\*")
| count_distinct(ImageLoaded) as TotalModules by Computer, Image, ProcessGuid
) on ProcessGuid
| where TotalModules < 5
| fields Computer, Image, CoreDLLLoads, TotalModules, LoadedLibraries
| sort by TotalModules ascSumo Logic query detecting dynamic API resolution by identifying Sysmon Event ID 7 records where core Windows DLLs are loaded by processes outside standard system directories, then joining on ProcessGuid to surface only those processes with a total module load count below 5. A very low TotalModules value paired with non-standard process path is a strong behavioral indicator of malware manually resolving API functions via LoadLibrary and GetProcAddress rather than relying on the PE loader's static import resolution.
Data Sources
Required Tables
False Positives & Tuning
- Minimally-linked legitimate applications written in low-level languages (Rust, Go, Zig) that explicitly call LoadLibrary for a small set of DLLs and run from build output or portable directories
- Developer test binaries compiled locally and executed from project build directories that include only essential runtime DLL imports during early-stage development
- Containerized or sandboxed execution environments where processes are launched from non-standard mount paths and operate with a restricted DLL load profile by design
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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