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Yahoo! Bug Bounty #29 YM - Filter Bypass & Persistent Web Vulnerability
Jul 10 2014 12:47PM
Vulnerability Lab (research vulnerability-lab com)
Yahoo! Bug Bounty #29 YM - Filter Bypass & Persistent Web Vulnerability
Vulnerability Laboratory ID (VL-ID):
Common Vulnerability Scoring System:
Product & Service Introduction:
Yahoo! Inc. is an American multinational internet corporation headquartered in Sunnyvale, California. It is widely known
for its web portal, search engine Yahoo! Search, and related services, including Yahoo! Directory, Yahoo! Mail, Yahoo!
News, Yahoo! Finance, Yahoo! Groups, Yahoo! Answers, advertising, online mapping, video sharing, fantasy sports and its
social media website. It is one of the most popular sites in the United States. According to news sources, roughly 700
million people visit Yahoo! websites every month. Yahoo! itself claims it attracts `more than half a billion consumers
every month in more than 30 languages.
(Copy of the Vendor Homepage: http://www.yahoo.com )
Abstract Advisory Information:
The Vulnerability-Laboratory Research Team has discovered multiple vulnerabilities in the official Yahoo! Messenger software v126.96.36.199 application.
Vulnerability Disclosure Timeline:
2013-07-31: Researcher Notification & Coordination (Ateeq ur Rehman Khan - Core Research Team)
2013-08-01: Vendor Notification (Yahoo! Security Team - Bug Bounty Program)
2013-09-01: Vendor Response/Feedback (Yahoo! Security Team - Bug Bounty Program)
2014-06-01: Vendor Fix/Patch (Yahoo! Developer Team - Reward: HackerOne Program)
2014-07-07: Public Disclosure (Vulnerability Laboratory)
Product: Yahoo! Messenger Desktop (US) 188.8.131.52 (US)
Technical Details & Description:
An input filter bypass & persistent web vulnerability has been discovered in the official Yahoo! Messenger (184.108.40.206-us) Desktop Application.
The persistent remote web vulnerability affects the software exception handling module of the phone `SMS` feature in the application.
It was initially discovered that while sending an `SMS`, the Yahoo IM application validates all entered numbers through a
remote host: validate.msg.yahoo.com. If the number is invalid/malicious the remote host responds with an `unknown number` exception
which is then handled by the IM application in a new msg window. While handling the exception, the injected code gets executed
successfully in the new msg window where the exception is processed as HTML.
Malicious requests can be injected in the `Enter Mobile Number` input field using a filter bypass technique while sending an SMS
through the Yahoo IM application. It seems that basic security controls are in place to restrict user from typing in Alphabets and
special characters when sending an SMS however a simple copy/paste of a specially crafted payload bypasses the restriction quite
easily and results in successful code execution of the injected scripts code.
The security risk of the filter bypass and persistent vulnerability is estimated as high with a cvss (common vulnerability scoring
system) count of 6.3.
This type of vulnerability can be exploited by a non privileged / unauthorized remote attackers and requires a normal application
user account (victim). The successful exploitation of the remote vulnerability results in session hijacking, persistent phishing,
persistent external redirect, persistent external malware loads and persistent manipulation of affected module context.
[+] Yahoo! Messenger - Desktop Application v220.127.116.11-us (software)
[+] Enter Mobile Number
[+] Send An SMS > Mobile Number
Proof of Concept (PoC):
The persistent input validation web vulnerability can be exploited by remote attackers with low user interaction and low privileged
web application user account. For demonstration or to reproduce ...
Manual steps to reproduce the vulnerability ...
1. Login to your Yahoo IM application
2. Click on the Send an SMS icon
3. Inject the "Payload" in the "Enter Mobile Number" input field
4. A new IM window should popup and shortly your browser should be redirected to my website proving the existence of this vulnerability
'%3d'>"><iframe src='http://vulnerability-lab.com' onload=window.location=('http://evolution-sec.com')></iframe>/927
--- PoC Session Logs ---
HTTP Requests: POST /mobileno?intl=us&version=18.104.22.168 HTTP/1.1
User-Agent: Mozilla/4.0 (compatible; MSIE 5.5)
<validate intl="us" version="22.214.171.124" qos="0"><mobile_no msisdn="1334372637724887885637224548952226666562325378762437263927"></mo
HTTP/1.1 200 OK
Date: Wed, 06 Nov 2013 12:52:31 GMT
P3P: policyref="http://info.yahoo.com/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi
TELo OTPi OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR
FIN COM NAV INT DEM CNT STA POL HEA PRE LOC GOV"
Content-Type: text/html; charset=utf-8
Solution - Fix & Patch:
Proper security controls should be implemented/enforced in the IM application to validate input and restrict copy/paste of
malicious requests in all affected input fields. Also restricting the exceptions response type so they are not processed as
HTML by the IM application is recommended.
The security risk of the persistent exception-handling web vulnerability is estimated as high(-).
Credits & Authors:
Vulnerability Laboratory [Research Team] - Ateeq ur Rehman Khan (ateeq (at) evolution-sec (dot) com [email concealed]) [www.vulnerability-lab.com]
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