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                             Luigi Auriemma

Application:  libmusicbrainz
              http://musicbrainz.org/doc/libmusicbrainz
Versions:     <= 2.1.2 and <= SVN 8406 (current SVN)
Platforms:    Windows, *nix, *BSD, Mac and others
Bugs:         A] buffer-overflow in MBHttp::Download
              B] various buffer-overflows in rdfparse.c
Exploitation: remote
Date:         13 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
===============


libmusicbrainz (aka mb_client) is an open source library used in many
multimedia programs for querying MusicBrainz servers.


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

--------------------------------------
A] buffer-overflow in MBHttp::Download
--------------------------------------

A malicious MusicBrainz web server can exploit a buffer-overflow in the
Download function of the library through a big redirect HTTP reply
(Location).
This bug can be exploited also in other local ways since the problem is
located in the instructions which handle the URL's hostname.

From lib/http.cpp:

Error MBHttp::Download(const string &url, const string &xml, bool fileDownload)
{
    Error          result = kError_InvalidParam;
    char           hostname[kMaxHostNameLen + 1];
    char           targethostname[kMaxHostNameLen + 1];
    char           proxyname[kMaxURLLen + 1];
    ...
            const char *ptr;
            hostname[0] = 0;
            numFields = sscanf(url.c_str(), 
                           "http://%[^:/]:%hu", hostname, &port);
            strcpy(targethostname, hostname);
            ptr = strchr(url.c_str() + 7, '/');
            file = string(ptr ? ptr : "");
            ...
                // 3xx: Redirection - Further action must be taken in order to
                // complete the request
                case '3':
                {
                    char* cp = strstr(buffer, "Location:");
                    //int32 length;

                    if(cp)
                    {
                        cp += 9;

                        if(*cp == 0x20)
                            cp++;

                        char *end;
                        for(end = cp; end < buffer + total; end++)
                            if(*end=='\r' || *end == '\n') break;

                        *end = 0x00;
                        ...
                            result = Download(string(cp), xml, fileDownload);
                        }
                        ...


-----------------------------------------
B] various buffer-overflows in rdfparse.c
-----------------------------------------

The instructions in lib/rdfparse.c which parse the RDF data received
from the server are affected by various buffer-overflows exploitable
with long URLs (like a big rdf:resource field) copied in buffers of 256
bytes.

For example in parse_uri the len parameter containing the size of
buffer (one of the base_buffer or reference_buffer buffers of 256 bytes
declared in resolve_uri_reference) is not checked so a long URI will
cause a buffer overflow.
The same function which calls parse_uri is affected by other buffer
overflows for the same reason, the length value is not verified.
Same problem for resolve_id and many other functions.


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


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

usage examples:
A] nc -l -p 80 -v -v -n < brainzbof_a.txt
B] nc -l -p 80 -v -v -n < brainzbof_b.txt


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


A new version will be released soon


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