Breaking Instacart

Instacart is an American company that operates as a same-day grocery delivery service. Customers select groceries through a web application from various retailers and delivered by a personal shopper. As of 2017, Instacart only has operations and services in the United States. [1]

Instacart has a bug bounty program on Hackerone, you can learn more about it at I’ve reported multiple valid security issues(ranked #2, ), this one is worth sharing.

Instacart has a hiring section for shoppers, where a potential candidate can enter his details and set up a meeting.

The Auth part was this section was the interesting part.

One day I received an email which said “set up your meeting”, I clicked the linked and it logged me in without asking any credentials.

After breaking down the Auth link, found out it was GET request with pin code, phone number, and a verification code which was in the format

The login process from the ‘sign-in’ page required an OTP sent to the registered mobile. Tried to log in multiple times from the login page, surprising part was getting the same OTP every time.

In order to show the impact, the attack must be applicable to all accounts.

Obviously, the first attempt would be brute forcing the login form with known mobile number and as the verification code consists 5 digits. We can start from 00000 to 99999 but that didn’t work, got blocked by rate limit after certain attempts.

As it was a GET request, one can brute force the URL itself. Just brute force the code part for a known number in the URL

And it worked!

Though the whole attack depends upon a known pin code and mobile number, Instacart accepted the report as medium severity and paid their highest bounty of that time.

Later, Instacart replaces the auth part with Twitter fabric.

Thanks for reading. If you have any suggestions or feedback, feel free to reach out on Twitter

Manish 🙂



Hacking Google for fun and profit

I have been doing bug bounties since September 2013(Asana was the first), participated and qualified in almost all bug bounties at least once. My bucket list had Facebook, Yahoo, Twitter, Dropbox, Github and 100+ such sites (including couple of YC Startups ) but Google VRP was tough nut to crack. I always wanted to start my bug bounty story with Google, but failed in past with few duplicates.

I was watching 2016 Google I/O, Firebase was the main focus. I had reported couple of security issues when they were quite young. Got a mini box full of stickers, bands and hot souces for my contribution.


So when I saw Firebase got a new site that too on a *,  it all came back to me.

The minimum bounty on Google main domain(* is $500, more than that you’ll get your name in prestigious Google Hall of Fame.
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Understanding CSRF attacks


What is CSRF ?

“Cross-site request forgery, also known as one-click attack or session riding and abbreviated as CSRF (sometimes pronounced sea-surf) or XSRF, is a type of malicious exploit of a website where unauthorized commands are transmitted from a user that the website trusts.” – Wikipedia

CSRF is at 8th position in OWASP top 10 bug list. Usage of frameworks like Django, ROR reduces the risk of CSRF to a large extent but it is still there. Also, it is carried out from user’s IP address, website’s logs will have no evidence.

Examples of CSRF:

CSRF comes in all shape and sizes. Dangerous one can take over an account, minor one can destroy your session or log you out.

Every request that change state on server should have CSRF protection.

It can be an email change or addition of user details like a bank account.
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Web application security checklist

I printed out my Asana task list of web app security testing,hopefully you’ll find it useful. OWASP 10 are the starting points of web testing, followed by other not so common issues.

Comments inside my task list are more helpful(provide various attack scenario and test cases) but Asana don’t export  comments while printing, maybe I’ll write a proper short guide explaining all the points in future. Stay tuned on my twitter for further updates.

Here is the PDF of Security task list



Manish (@umenmactech)