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IsDebuggerPresent
This function checks specific flag in the Process Environment Block (PEB) for the field IsDebugged which will return zero if the process is not running into a debugger or a nonzero if a debugger is attached.
If you want to understand the underlying process of IsDebuggerPresent API you can check the code snippet section for the following method: IsDebugged …
Read moreCheckRemoteDebuggerPresent
CheckRemoteDebuggerPresent is a kernel32.dll function that sets (-1)0xffffffff in the DebuggerPresent parameter if a debugger is present. Internally, it also uses NtQueryInformationProcess with ProcessDebugPort as a ProcessInformationClass parameter.
Read moreDebugger Evasion
![Defense Evasion [Mitre] icon](/media/2024/04/08/icons8-burglar.svg){kind=small}
Adversaries may employ various means to detect and avoid debuggers. Debuggers are typically used by defenders to trace and/or analyze the execution of potential malware payloads.
Debugger evasion may include changing behaviors based on the results of the checks for the presence of artifacts indicative of a debugged environment. Similar to Virtualization/Sandbox Evasion, if the adversary detects a debugger, …
Read moreTLS Callback
TLS (Thread Local Storage) callbacks are a mechanism in Windows that allows a program to define a function that will be called when a thread is created. These callbacks can be used to perform various tasks, such as initializing thread-specific data or modifying the behavior of the thread.
As an anti-debugging technique, a program can use a TLS callback …
Read moreBad String Format
Bad string format is a technique used by malware to evade detection and analysis by OllyDbg, a popular debugger used by security researchers and analysts. This technique involves using malformed strings that exploit a known bug in OllyDbg, causing the debugger to crash or behave unexpectedly.
For example, the malware may use a string with multiple %s inputs, which …
Read moreAbusing the Return Pointer
Abusing the return pointer is an anti-disassembling technique that involves using the return instruction (RETN) in a way that is not expected by the disassembler. This can make it more difficult for the disassembler to accurately reconstruct the program's original instructions and can also make it more difficult for analysts to understand the program's behavior.
The RETN instruction is …
Read moreNtSetDebugFilterState
The NtSetDebugFilterState and DbgSetDebugFilterState functions are used by malware to detect the presence of a kernel mode debugger. These functions allow the malware to set up a debug filter, which is a mechanism that can be used to detect and respond to the presence of a debugger.
When a kernel mode debugger is present, the debug filter will be …
Read moreGuard Pages
Memory breakpoints are a technique used by malware to detect if a debugger is present. This technique involves setting up a "guard page" in memory, which is a page of memory that is protected by the operating system and cannot be accessed by normal code. If a debugger is present, the malware can use this guard page to detect its …
Read moreNtQueryInformationProcess
This function retrieves information about a running process. Malware are able to detect if the process is currently being attached to a debugger using the ProcessDebugPort (0x7) information class.
A nonzero value returned by the call indicates that the process is being debugged.
Read moreNtSetInformationThread
NtSetInformationThread can be used to hide threads from debuggers using the ThreadHideFromDebugger ThreadInfoClass (0x11 / 17). This is intended to be used by an external process, but any thread can use it on itself.
After the thread is hidden from the debugger, it will continue running but the debugger won’t receive events related to this thread. …
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