ID	B0003
Objective(s)	Anti-Behavioral Analysis
Related ATT&CK Techniques	Virtualization/Sandbox Evasion (T1497, T1633)
Anti-Analysis Type	Evasion
Version	2.2
Created	1 August 2019
Last Modified	27 April 2024

Dynamic Analysis Evasion

Malware may obstruct dynamic analysis in a sandbox or virtual machine. An analyst detonates the specimen in these controlled environments to understand the malware's behavior. However, the code may exhibit a variety of anti-analysis methods, including delayed execution and code integrity checks. Additional methods are listed in the table below.

See Emulator Evasion (B0004) for an emulator-specific evasion behavior, and see Conditional Execution (B0025) for a behavior that constrains dynamic execution based on environmental conditions.

The related Virtualization/Sandbox Evasion (T1497, T1633) ATT&CK techniques were defined subsequent to this MBC behavior.

Methods

Name	ID	Description
Alternative ntdll.dll	B0003.001	A copy of ntdll.dll is dropped to the filesystem and then loaded. This alternative DLL is used to execute function calls to evade sandboxes which use hooking in the operating system's ntdll.dll.
API Hammering	B0003.012	Uses of a huge number of calls to Windows APIs as a form of extended sleep to evade analysis in sandbox environments. This method is related to Unprotect technique U1305.
Code Integrity Check	B0003.011	Compares memory-based and disk-based versions of itself. If differences are detected, the malware alters its execution, possibly acting destructively.
Data Flood	B0003.002	Overloads a sandbox by generating a flood of meaningless behavioral data. [1]
Delayed Execution	B0003.003	Stalling code is typically executed before any malicious behavior. The malware's aim is to delay the execution of the malicious activity long enough so that an automated dynamic analysis system fails to extract the interesting malicious behavior. This method is very similar to ATT&CK's Virtualization/Sandbox Evasion: Time Based Evasion sub-technique. This method is related to Unprotect technique U1318.
Demo Mode	B0003.004	Inclusion of a demo binary/mode that is executed when token is absent or not privileged enough.
Drop Code	B0003.005	Original file is written to disk then executed. May confuse some sandboxes, especially if the dropped executable must be provided specific arguments and the original dropper is not associated with the drop file(s).
Encode File	B0003.006	Encode a file on disk, such as an implant's config file.
Hook File System	B0003.007	Execution happens when a particular file or directory is accessed, often through hooking certain API calls such as CreateFileA and CreateFileW.
Hook Interrupt	B0003.008	Modification of interrupt vector or descriptor tables.
Illusion	B0003.009	Creates an illusion; makes the analyst think something happened when it didn't.
Restart	B0003.010	Restarts or shuts down system to bypass sandboxing.

Use in Malware

Name	Date	Method	Description
Terminator	2013	B0003.003	The Terminator RAT evades a sandbox by not executing until after a reboot. Most sandboxes don't reboot during an analysis. [3]
Nap	2013	--	Trojan Nap (tied to the Kelihos Botnet) uses extended sleep calls to evade sandbox analysis. [3]
Smokeloader	2019	--	Smokeloader drops a copy of ntdll.dll to %APPDATA%\Local\Temp\ [4]
WebCobra	2018	B0003.001	The malware loads ntdll.dll and user32.dll as data files and overwrites the first 8 bytes of those functions to avoid API hooking by security products. [7]
Rombertik	2015	B0003.002	The malware stalls by writing a byte of random data to memory 960 million times which complicates analysis. It also calls specific Windows API functions. [5]
Rombertik	2015	B0003.011	The malware computes a 32-bit hash of a resource in memory, and compares it to the PE Compile Timestamp of the unpacked sample. If the resource or compile time has been altered, the malware acts destructively. [5]
TrickBot	2016	B0003.012	The malware uses numerous printf loops to delay the execution process and overload the sandbox with junk data (API Hammering). [6]

Detection

Tool: capa	Mapping	APIs
delay execution	Dynamic Analysis Evasion::Delayed Execution (B0003.003)	kernel32.Sleep, kernel32.SleepEx, kernel32.WaitForSingleObject, kernel32.SignalObjectAndWait, kernel32.WaitForSingleObjectEx, kernel32.WaitForMultipleObjects, kernel32.WaitForMultipleObjectsEx, kernel32.RegisterWaitForSingleObject, WaitOnAddress, user32.MsgWaitForMultipleObjects, user32.MsgWaitForMultipleObjectsEx, NtDelayExecution, KeWaitForSingleObject, KeDelayExecutionThread, sleep, usleep

Tool: CAPE	Mapping	APIs
api_spamming	Dynamic Analysis Evasion (B0003)	--
api_spamming	Dynamic Analysis Evasion::Data Flood (B0003.002)	--
api_spamming	Dynamic Analysis Evasion::Delayed Execution (B0003.003)	--
antisandbox_suspend	Dynamic Analysis Evasion (B0003)	NtSuspendThread
antisandbox_restart	Dynamic Analysis Evasion (B0003)	ExitWindowsEx, InitiateSystemShutdownExW, NtSetSystemPowerState, InitiateSystemShutdownW, InitiateShutdownW, NtRaiseHardError, NtShutdownSystem
antisandbox_restart	Dynamic Analysis Evasion::Restart (B0003.010)	ExitWindowsEx, InitiateSystemShutdownExW, NtSetSystemPowerState, InitiateSystemShutdownW, InitiateShutdownW, NtRaiseHardError, NtShutdownSystem
stealth_timeout	Dynamic Analysis Evasion (B0003)	NtWaitForSingleObject, NtQuerySystemTime, NtTerminateProcess, GetLocalTime, NtDelayExecution, GetSystemTime, GetSystemTimeAsFileTime
stealth_timeout	Dynamic Analysis Evasion::Delayed Execution (B0003.003)	NtWaitForSingleObject, NtQuerySystemTime, NtTerminateProcess, GetLocalTime, NtDelayExecution, GetSystemTime, GetSystemTimeAsFileTime
antisandbox_unhook	Dynamic Analysis Evasion (B0003)	--

B0003.003 Snippet

Anti-Behavioral Analysis::Dynamic Analysis Evasion::Delayed Execution

SHA256: 21c1fdd6cfd8ec3ffe3e922f944424b543643dbdab99fa731556f8805b0d5561 Location: 0x40103B

push    0x36ee80        ; sleep duration: 3600000 milliseconds (1 hour)
call    dword ptr [->KERNEL32.DLL::Sleep]       ; Windows API call instructing thread to sleep for the time period specified above