Zomato is an online restaurant search and discovery service providing information on home delivery, dining-out, cafés and nightlife for various cities of India and 21 other countries. It has 62.5 million registered users.
While creating an account, a user can store his phone number, addresses, date of birth, link Instagram account etc. In one of the API call, they were reflecting the user data based on the "browser_id" parameter in the API request. Interestingly, changing the "browser_id" sequentially resulted in data leakage of other Zomato users. The data leaked also had Instagram access token which could be used to see private photos on Instagram of respective Zomato users.
Below are the technical details of the vulnerability:
Insecure Direct Object References occur when an application provides direct access to objects based on user-supplied input. As a result of this vulnerability, attackers can bypass authorization and access resources in the system directly, for example database records or files.
Insecure Direct Object References allow attackers to bypass authorization and access resources directly by modifying the value of a parameter used to directly point to an object. Such resources can be database entries belonging to other users, files in the system, and more. This is caused by the fact that the application takes user supplied input and uses it to retrieve an object without performing sufficient authorization checks.
POST /v2/userdetails.json/XXXXX?&browser_id=XXXXX&type=journey&lang=en&uuid=pgh1evyBWvL+sp9/JpwUpItnk8Q=&app_version=188.8.131.52 HTTP/1.1
Accept-Encoding: gzip, deflate
Replacing the XXXXX with victim's user id in the above request led to information disclosure.
Ease of exploitability:
You can easily get userid of any zomato user by visting their profile. They are public and appended to your profile url.
Proof of concept video:
This bug was responsibly disclosed to Zomato and was fixed within few minutes by the engineering team.
June 1, 2015 09:29 PM : Report sent to Deepinder Goyal, CEO
June 2, 2015 12:54 PM : Added Gunjan Patidar, CTO and Shrey Sinha to the mail thread
June 2, 2015 1:04 PM : Bug acknowledged by Gunjan Patidar
June 2, 2015 2:01 PM : Confirmation of vulnerability fix from Gunjan Patidar.