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NixImports
A .NET malware loader employs API-Hashing and dynamic invocation to circumvent static analysis. NixImports utilizes managed API-Hashing to dynamically determine most of its required functions during runtime. For function resolution, HInvoke needs two specific hashes: typeHash and methodHash, representing the type name and the method's full name, respectively. At runtime, HInvoke scans the entire mscorlib to locate the corresponding type …
Read moreBuildCommDCBAndTimeoutA
This technique uses a BuildCommDCBAndTimeoutsA API call to determine if the malware is detonating in a sandbox. Normally, a bogus device string would cause this API call to fail. However, some malware sandbox environments may emulate in a way that allows the API call to succeed even when given a bogus device string.
NtDelayExecution
NtDelayExecution can be used to delay the execution of the calling thread. NtDelayExecution accepts a parameter "DelayInterval", which is the number of milliseconds to delay. Once executed, NtDelayExecution "pauses" execution of the calling program whuch can cause a timeout of the sandbox or loss of control in a debugger.
Additionally, some higher level WinAPI functions invoke NtDelayExeuction. For example, …
Read moreIPV4/IPV6 Obfuscation
The obfuscated payload masquerades itself as an array of ASCII IPv4 addresses. Each one of these IPs is passed to the RtlIpv4StringToAddressA function, which will translate the ASCII IP string to binary. The binary representation of all of these IPs is combined to form a blob of shellcode. Additionally, IPfuscation variants were spotted using IPv6 instead of IPv4 addresses, UUIDs, …
Al-Khaser_WriteWatch
Default invalid parameter values of Al-Khaser's Anti-Debug technique (VirtualAlloc/MEM_WRITE_WATCH). Used for checking API hooks in debuggers/sandboxes.
Read morebochs CPU oversights evasion
bochs has multiple oversights in its CPU emulation, which allows us to detect if we're running in a bochs emulator:
bochs may have invalid CPU brands that don't exist.
- For AMD CPUs, the "p" in "processor" should be in capital, which bochs doesn't implement.
- AMD CPUs have easter eggs for their K7 and K8 CPUs ("IT'S …
Indirect Memory Writing
In local memory movement scenarios, for example, when a loader places a payload into memory for execution, antimalware can detect malicious activity at the moment the payload bytes are written into the newly allocated executable memory region. Attackers may try to evade such detection by avoiding direct writes to new memory region and instead relying on other, legitimate Windows APIs …
Read moreSuspendThread
Suspending threads is a technique used by malware to disable user-mode debuggers and make it more difficult for security analysts to reverse engineer and analyze the code. This can be achieved by using the SuspendThread function from the kernel32.dll library or the NtSuspendThread function from the NTDLL.DLL library.
The malware can enumerate the threads of a given process, or …
Read moreDebug Registers, Hardware Breakpoints
Hardware breakpoints allow a debugger to pause execution at specific memory addresses without modifying the program code. They are stored in special CPU registers (DR0 through DR3 on Intel CPUs).
For anti-debugging, malware can inspect the values of these debug registers. If any of the registers contain a non-empty value, it indicates that a hardware breakpoint has been set …
Read moreLocalSize(0)
The function LocalSize retrieves the current size of the specified local memory object, in bytes. By setting the hMem parameters with 0 will trigger an exception in a debugger that can be used as an anti-debugging mechanism.