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                             Luigi Auriemma

Application:  OpenMPT (aka MODPlug Tracker)
                http://modplug.sourceforge.net
                http://www.modplug.com
              libmodplug
                http://modplug-xmms.sourceforge.net
Versions:     OpenMPT    <= 1.17.02.43 and current SVN
              libmodplug <= 0.8 and current CVS
Platforms:    Windows
              *nix, *BSD, XMMS plugin and others
Bugs:         A] various global buffer overflows in ReadITProject
              B] heap overflow in ReadSample
Exploitation: local
Date:         09 Aug 2006
Author:       Luigi Auriemma
              e-mail: aluigi@autistici.org
              web:    aluigi.org


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1) Introduction
2) Bugs
3) The Code
4) Fix


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===============
1) Introduction
===============


MODPlug Tracker, and naturally its more recent open source version
OpenMPT, is one of the coolest music trackers which supports many music
module types too.
libmodplug instead is a Linux library created from the OpenMPT source
and mainly used for the ModPlug-XMMS plugin.


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=======
2) Bugs
=======

---------------------------------------------------
A] various global buffer overflows in ReadITProject
---------------------------------------------------

All the text fields in the ITP files are not sanitized so is possible
to overflow the global variables through this function and possibly
executing malicious code (confirmed in my tests).
Note: ITP files are not supported in libmodplug

From soundlib/Load_it.cpp:

BOOL CSoundFile::ReadITProject(LPCBYTE lpStream, DWORD dwMemLength)
{
    ...
// Song name

    // name string length
    memcpy(&id,lpStream+streamPos,sizeof(DWORD));
    len = id;
    streamPos += sizeof(DWORD);

    // name string
    memcpy(&m_szNames[0],lpStream+streamPos,len);
    streamPos += len;
    ...
    (other overflows)
    ...


------------------------------
B] heap overflow in ReadSample
------------------------------

In some modules the ReadSample function can be used to cause a heap
overflow through an invalid nLength value.
As visible by the code below, nLength is incremented of 6 bytes (mem)
and in some cases its value is multiplicated by two, the final value is
then used to allocate pIns->pSample (FYI AllocateSample allocates
"(nbytes + 39) & ~7" and returns the pointer plus 16).
An attacker, after having forced the program to allocate 0 bytes, will
be able to overflow the memory through the memcpy instructions which
will copy (depending by nFlags) all the remaining bytes in the file.
The best type of module for exploiting this vulnerability seems to be
AMF.

From soundlib/Sndfile.cpp:

UINT CSoundFile::ReadSample(MODINSTRUMENT *pIns, UINT nFlags, LPCSTR lpMemFile, DWORD dwMemLength)
//------------------------------------------------------------------------------------------------
{
    UINT len = 0, mem = pIns->nLength+6;

    if ((!pIns) || (pIns->nLength < 4) || (!lpMemFile)) return 0;
    if (pIns->nLength > MAX_SAMPLE_LENGTH) pIns->nLength = MAX_SAMPLE_LENGTH;
    ...
    if ((pIns->pSample = AllocateSample(mem)) == NULL)
    ...
    default:
        len = pIns->nLength;
        if (len > dwMemLength) len = pIns->nLength = dwMemLength;
        memcpy(pIns->pSample, lpMemFile, len);
    }
    ...


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===========
3) The Code
===========


http://aluigi.org/poc/mptho.zip


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======
4) Fix
======


A new version will be released soon


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