LocalSize(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.

Technique Identifier

U0128

Technique Tag

localsize

Evasion Categories

Anti-Debugging

Code Snippets

#include <iostream>
#include <windows.h>

using namespace std;

int main()
{
	SIZE_T s;
	printf("Starting the LocalSize()\n");
	for (int i = 0; i < 0xFFF; i++){
	    s = LocalSize(0);
	}
	printf("Sempai! :) \n");
	return 0;
}

About Author Open Snippet

Author: Fumik0_ / Target Platform: Windows

Detection Rules

rule Detect_LocalSize: AntiDebug {
    meta: 
        description = "Detect LocalSize as anti-debug"
        author = "Unprotect"
        comment = "Experimental rule"
    strings:
        $1 = "LocalSize" fullword ascii
    condition:   
       uint16(0) == 0x5A4D and filesize < 1000KB and $1
}

rule:
  meta:
    name: trap debugger with localsize
    namespace: anti-analysis/anti-debugging
    author: lordtmk@protonmail.com
    scope: basic block
    examples:
      - B67E5B1985742F62785122B637EF4FBD:0x4B1F5B
  features:
    - and:
      - api: LocalSize
      - mnemonic: push 
      - number: 0

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

LocalSize function (winbase.h) - Win32 apps | Microsoft Docs

Matching Samples 10 most recent

Sample Name	Matching Techniques	First Seen	Last Seen
al-khaser.exe	24	2024-11-13	1 year, 4 months ago

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Created

April 29, 2021

Last Revised

March 24, 2026