Document Title: =============== Prezi Bug Bounty #5 - Client Side Cross Site Scripting & Open Redirect Vulnerability References (Source): ==================== Release Date: ============= 2016-02-19 Vulnerability Laboratory ID (VL-ID): ==================================== 1724 Common Vulnerability Scoring System: ==================================== 3 Product & Service Introduction: =============================== Prezi is a cloud-based presentation software based on a software as a service model. The product employs a zooming user interface (ZUI), which allows users to zoom in and out of their presentation media, and allows users to display and navigate through information within a 2.5D or parallax 3D space on the Z-axis. Prezi was officially established in 2009 by co-founders Adam Somlai-Fischer, Peter Halacsy and Peter Arvai. (Copy of the Wikipedia entry: Abstract Advisory Information: ============================== An independent vulnerability laboratory researcher discovered a client-side redirect web vulnerability in the official Prezi web-application. Vulnerability Disclosure Timeline: ================================== 2016-00-29: Researcher Notification & Coordination (Milan Solanki) 2016-00-30: Vendor Notification (Prezi Security Team) 2016-00-04: Vendor Response/Feedback (Prezi Security Team) 2016-00-16: Vendor Fix/Patch #1 (Prezi Developer Team) 2016-00-22: Security Acknowledgements (Prezi Security Team) 2016-00-17: Security Bulletin (Prezi Security Team) 2016-00-18: Public Disclosure (Vulnerability Laboratory) Discovery Status: ================= Published Affected Product(s): ==================== Prezi Product: Online Service - Web Application 2016 Q1 Exploitation Technique: ======================= Remote Severity Level: =============== Medium Technical Details & Description: ================================ An open redirect web vulnerability has been discovered in the official Prezi web-application. The bug allows remote attackers to execute external urls by the internal web-application requests via client-side. The vulnerability is located in the GET parameter of the vulnerable `track` module. The vulnerability allows an remote attacker to prepare client-side malicious urls to external sources. The request method to execute is GET and the vulnerability is located on the application-side of the online-service. The vulnerability is a classic open redirect web vulnerability. The security risk of the open redirect web vulnerability is estimated as medium with a cvss (common vulnerability scoring system) count of 3.0. Exploitation of the persistent input validation web vulnerability requires no privileged user account and low or medium user interaction. Successful exploitation of the vulnerability results in client-side redirects to malicious sources or client-side phishing. Request Method(s): [+] GET Vulnerable Module(s): [+] /track Vulnerable Parameter(s): [+] URI Proof of Concept (PoC): ======================= The vulnerability can be exploited by remote attackers without privileged web-application user account and with low or medium user interaction. For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue. Vulnerability: Open redirect in the following module: /track?type=click&enid=[UNIQUE-ID]&&&2003&&& PoC: saWQ9bWFzaGFjazQyM0BnbWFpbC5jb20mdXNlcmlkPTFfMTU1MTYzJnRhcmdldGlkPSZtbj04MTE1NDQmZmw9Jm12aWQ9JmV4dHJhPSYmJg==&&&2003&&& Solution - Fix & Patch: ======================= Disallow to request not whitelisted webpages and include a tag filter to the enid to prevent as well. Restrict and filter the parameter and disallow usage of special chars. Encode the GET request to prevent client-ide script code inject. Security Risk: ============== The security risk of the client-side open redirect web vulnerability in the Prezi web-application is estimated as low. (CVSS 3.0) Credits & Authors: ================== Milan A Solanki - ( [] [] 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. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply. 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