Bugcrowd Persistent Script Injection / Filter Bypass
Posted on 27 May 2016
Document Title: =============== Bugcrowd Bug Bounty #7 - Persistent Web Vulnerability References (Source): ==================== http://www.vulnerability-lab.com/get_content.php?id=1830 ID: b40f63ed19074014df808599e44684f6a18bb6f4f51cf21948ef78df2f56c13b Release Date: ============= 2016-05-10 Vulnerability Laboratory ID (VL-ID): ==================================== 1830 Common Vulnerability Scoring System: ==================================== 3.8 Product & Service Introduction: =============================== >From the outback to the valley, Bugcrowd is paving the way for crowdsourced security. Founded in 2012 in Australia by Casey Ellis, Bugcrowd is now based in San Francisco and is backed by Costanoa Venture Capital, Rally Ventures, Paladin Capital Group and Blackbird Ventures. (Copy of the Homepage: https://bugcrowd.com/about ) Abstract Advisory Information: ============================== The vulnerability laboratory research team discovered an application-side vulnerability in the official Bugcrowd online service web-application. Vulnerability Disclosure Timeline: ================================== 2016-04-20: Researcher Notification & Coordination (Benjamin Kunz Mejri - Evolution Security GmbH) 2016-04-21: Vendor Notification (Bugcrowd - Bug Bounty Program) 2016-**-**: Vendor Fix/Patch (Bugcrowd - Bug Bounty Program) 2016-05-03: Acknowledgement & Bug Bounty (Bugcrowd - Bug Bounty Program) 2016-05-10: Public Disclosure (Vulnerability Laboratory) Discovery Status: ================= Published Affected Product(s): ==================== Bugcrowd Product: Online Service - Web Application 2016 Q2 Exploitation Technique: ======================= Remote Severity Level: =============== Medium Technical Details & Description: ================================ A persistent script code injection and application-side mail encode web vulnerability has been discovered in the official Bugcrowd online service web-application. The vulnerability typ allows an attacker to inject own malicious script code to the application-side of the vulnerable service function or web modules context. The bugcrowd service allows to register by a web formular in the webpage to receive new information like "... Bugcrowd`s Next Chapter". In the name values attackers are able to inject malicious script codes. In an advisory send to bugcrowd about 1 year ago we already mentioned the problem but your team was not able to verify the bug finally. Thus time we exploited the bug by using casey ellis wrong encoded context of the bugcrowd registered users to stream the code with the service emails. The injection point is the formular registration for receiving information of bugcrowd and the execution point is the email body context with the broken encode values. The code directly executes after the arrival in the main body context and the sender of the email was the mail support@bugcrowd inbox. The security risk of the application-side cross site web vulnerability is estimated as medium with a cvss (common vulnerability scoring system) count of 3.7. Exploitation of the persistent input validation web vulnerability requires a low privileged web-application user account and low or medium user interaction. Successful exploitation of the vulnerability results in session hijacking, persistent phishing attacks, persistent external redirects to malicious source and persistent manipulation of affected or connected application modules. Request Method(s): [+] POST Vulnerable Parameter(s): [+] Firstname [+] Lastname [+] Companyname Affected Module(s): [+] Email Community Letter - (community@bugcrowd.com) Proof of Concept (PoC): ======================= The security vulnerability can be exploited by remote attackers without user interaction or privileged web-application user account. For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue. PoC: Email: We've raised money, here's what's next from Bugcrowd (community@bugcrowd.com) - Casey Ellis <p style="margin-bottom: 1em; -webkit-text-size-adjust:100%; -ms-text-size-adjust:100%">Hi "><[PERSISTENT INJECTED SCRIPT CODE EXECUTION!]")" <="" "=""><iframe src=a onload=alert("PENTEST") <,</p> <p style="margin-bottom: 1em; -webkit-text-size-adjust:100%; -ms-text-size-adjust:100%">As you may have&nbsp;already heard, this morning we <a href="https://bugcrowd.com/resources/bugcrowd-15-million-raises-series-b" style="-webkit-text-size-adjust:100%; -ms-text-size-adjust:100%" data-hs-link-id="0">announced our $15M Series B funding</a>. We're proud to have many of our previous investors joining us again, as well as pleased to welcome new investors to the family. <br><br>We couldn't have done this without you. With your help we've built a massive&nbsp;community of hackers, made up of diverse and talented folks from all over the world.<br><br>We've got lots of plans for what's next and I've shared those details on our blog. Please check it out to learn more.<br><br><strong><a href="https://blog.bugcrowd.com/15-million-to-connect-hackers-and-companies-bugcrowd-series-b" style="-webkit-text-size-adjust:100%; -ms-text-size-adjust:100%" data-hs-link-id="1">Read about our plans for Bugcrowd's next chapter</a>.</strong> </p><p style="margin-bottom: 1em; -webkit-text-size-adjust:100%; -ms-text-size-adjust:100%">Thank you joining us on this journey. There's so much more to come! We hope you'll <a href="https://twitter.com/Bugcrowd/status/722904657366884353" style="-webkit-text-size-adjust:100%; -ms-text-size-adjust:100%" data-hs-link-id="0">join us today in our celebration</a> of this Bugcrowd community milestone.</p> <p style="margin-bottom: 1em; -webkit-text-size-adjust:100%; -ms-text-size-adjust:100%">Sincerely,</p> <p style="margin-bottom: 1em; -webkit-text-size-adjust:100%; -ms-text-size-adjust:100%">Casey Ellis<br>Bugcrowd Founder &amp; CEO</p></div> Solution - Fix & Patch: ======================= The vulnerability can be patched by a secure parse and encode of the vulnerable firstname, lastname and company values in the add POST method request. Disallow the usage of special chars in the name values, encode the inputs as well to prevent further exploitation. Encode as well outgoing emails to ensure that no malicious script code injection can take place with application-side attack vector. Security Risk: ============== The security risk of the filter bypass issue and application-side arbitrary script code injection web vulnerability is estimated as medium. (CVSS 3.8) Credits & Authors: ================== Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri (research@vulnerability-lab.com) [www.vulnerability-lab.com] [http://www.vulnerability-lab.com/show.php?user=Benjamin%20K.M.] Disclaimer & Information: ========================= The information provided in this advisory is provided as it is without any warranty. Vulnerability Lab disclaims all warranties, either expressed or implied, including the warranties of merchantability and capability for a particular purpose. Vulnerability-Lab or its suppliers are not liable in any case of damage, including direct, indirect, incidental, consequential loss of business profits or special damages, even if Vulnerability-Lab or its suppliers have been advised of the possibility of such damages. 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