In the name of Allah the beneficient the most merciful.It's been quite long time i wrote a blog due to some commitments , Today i would like to disclose one of my findings in Paypal which was reported via Hackerone.This bug allowed me to takeover all secondary accounts of any paypal business account , there was an IDOR bug which gave me control over any secondary user account i want.Paypal business accounts are used by millions of organizations worldwide and business ownersassign various privileges to secondary user accounts so as to ease their task. One of the privilege business owners give to secondary user is transfer money from paypal business account to any other account they like . So, i used this particular privilege in describing the issue which if exploited it would have given attacker unauthorized access to transfer money from any paypal business account by taking over secondary account of users having privilege as "Transfer money".Steps:Two different business accounts were needed for POC.-> From victim@gmail.com business account i created secondary userhaving username as victim1234-> From attacker@gmail.com business account i created secondary userhaving username as attacker1234-> From attacker account after going to secondary user accounthere https://www.paypal.com/businessmanage/users/1660971175791245038( this id is for attacker1234 , from attacker@gmail.com ) and then captured the requestto edit the permission like thisPUT /businessmanage/users/api/v1/users? HTTP/1.1Host: www.paypal.comConnection: close[{"id":"1660971175791245038","accessPoint":{"privileges":["MANUAL_REFERENCE_TXN","VIEW_CUSTOMERS","SEND_MONEY"],"id":"4446113495","accounts":["attacker@gmail.com"]},"roleID":0,"roleName":"CUSTOM","privilegeChanged":true,"privilegeSecondaryName":"ttt ttts"}]-> Now in the above PUT request the first id "it can be anything" i enteredid:"asdfjdsf"( some dummy value) and in the second id:446113495 , is the actual id of each secondary user which was vulnerable to IDOR.-> This second id is incremental and enumerable as it's only numbers.If attacker would have changed it to 44613496(lets suppose it is id of victim1234 ) then the associated secondary user account i.e., victim1234 would have been listed to him in https://www.paypal.com/businessmanage/users .-> This way if attacker would have just enumerated from 44613495 to 44613999 then all these secondary accounts would have been showed to him in Manage users section of attackers business account , then attacker just needed to change the password of user via Manage users section and Game over!!Complete takeover of any secondary account.-> After this attacker could have login to any secondary user account having privilege as "Transfer Money" and then it would have allowed him transfer money from victim account to attacker own account .Now Paypal remediated the issue and found no evidence of any kind of abuse associated with it.Summary by Paypal in hackerone about the issue.Thanks for reading.Hope you enjoyed reading it.RegardsMohd Hajihttps://www.linkedin.com/in/mohd-haji-490960a0/