Document Title: =============== PayPal Inc BB #127 - 2FA Bypass Vulnerability References (Source): ==================== Release Date: ============= 2016-08-12 Vulnerability Laboratory ID (VL-ID): ==================================== 1903 Common Vulnerability Scoring System: ==================================== 6.2 Product & Service Introduction: =============================== PayPal is a global e-commerce business allowing payments and money transfers to be made through the Internet. Online money transfers serve as electronic alternatives to paying with traditional paper methods, such as checks and money orders. (Copy of the Homepage: ) Abstract Advisory Information: ============================== The independent vulnerability laboratory researcher (shawar khan) discovered a vulnerability in the official PayPal website (api) web-application). The issue allows an attacker to bypass the 2-factor authentication and mobile confirmation which could lead to unauthorized access. Vulnerability Disclosure Timeline: ================================== 2016-05-13: Researcher Notification & Coordination (Shawar Khan) 2016-05-14: Vendor Notification (PayPal Inc Bug Bounty Program - Security Team) 2016-05-24: Vendor Response/Feedback (PayPal Inc Bug Bounty Program - Security Team) 2016-07-10: Vendor Fix/Patch (PayPal Inc Developer Team) 2016-07-18: Acknowledgements (PayPal Inc Bug Bounty Program - Security Team) 2016-08-12: Public Disclosure (Vulnerability Laboratory) Discovery Status: ================= Published Affected Product(s): ==================== PayPal Inc Product: PayPal - Online Service Web Application 2016 Q3 Exploitation Technique: ======================= Remote Severity Level: =============== High Technical Details & Description: ================================ A 2 Factor Authentication Bypass Vulnerability was discovered in the official PayPal website (api) web-application). This vulnerability allows an attacker to bypass the 2FA mechanism for access to accounts of paypal without verifying in the basic procedure the identity with confirmation. The security vulnerability is located in the paypal login portals of uk and the paypal preview. Each Portal is having an issue which can lead to a full bypass once used in a combined way. If the user have 2FA activated in his account. Whenever an user logs into his account, paypal will ask the user to verify the identity. Verification can be made via phone number or by confirming the login request via paypal mobile app (api). The mechanism mainly prevents unauthorized acccess to the account and provides an extra layer of security. The login portal of paypal preview is missing verification mechanism in it. When an user is logged in via paypal preview's login portal, the user is logged in without any verification and the login is successful but there is no settings or anything of interest. When logged in via paypal uk login portal, it checks if the user account is already signed in from any other portal or not. Once it checks the user is already logged in via paypal preview (without verification) it allows us access to the account without any kind of verification. This is the way how 2FA was bypassed in paypal due to lack of 2FA protection. Proof of Concept (PoC): ======================= PayPal uses an additional layer of security known as 2-Factor Authentication which is used to verify the user's identity so no unauthorized access would be allowed. The mechanism verifies the user's identity by calling or messaging a code to phone number or by confirming the login via Mobile App. Without these, the account will not be accessed. By following the procedure below the 2FA protection can be bypassed: Site: PayPal ( ) PayPal UK Login Portal: PayPal Preview Login Portal: Steps to reproduce: 1. Open PayPal UK Login Portal in a new tab(keep it open) 2. On the other tab, open PayPal Preview Login Portal 3. Login to your account in the URL which is opened in step 2 4. Enter credentials in the new window which appears 5. Refresh the page which was opened in step 1 6. Now you will be logged, Click on view account button which will lead you to your account and the 2 step verification will be bypassed Solution - Fix & Patch: ======================= In every login portals, verification checks must be deployed even if the user is already logged in. This will prevent unauthorized access to the account. Security Risk: ============== This vulnerability allows an attacker to bypass the 2-factor authentication and mobile confirmation which could lead to unauthorized access. Credits & Authors: ================== Shawar Khan - ( [] Disclaimer & Information: ========================= The information provided in this advisory is provided as it is without any warranty. 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