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 *google.com(https://firebase.google.com/),  it all came back to me.

The minimum bounty on Google main domain(*.google.com) 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)


List of Y Combinator companies I have worked with(hacked)


I have worked with lots of companies as security consultant through bug bounties either I asked them if they need my service or they approached. I’m a big fan of Paul’s essay, Hacker News, Startup School and YC as a whole, so thought to document my contribution to YC(nothing technical, just a list).

I have worked with these companies in their early stage to resolve security issues with their websites:

  1. Xobni (S06) :   Acquired by Yahoo later. Found account take over CSRF in setting page. Got Yahoo swags.
  2. Dropbox (S07):  Multiple bugs in the mailbox and other acquisitions. Got listed on Special Thanks page, swags and 100GB.
  3. Disqus (S07):  Got stickers and swags.(Can’t find the mail, don’t remember the issues)
  4. Heroku(W08):  Screen Shot 2015-10-28 at 11.49.39 am
  5. WePay (S09):  Participated in their bug bounty program on Hackerone.
  6. Olark (S09):    Screen Shot 2015-10-28 at 11.58.44 am
  7. Mixpanel(S09): Screen Shot 2015-10-28 at 12.02.29 pm
  8. Stripe(S10):Screen Shot 2015-10-28 at 12.06.52 pm
  9. PagerDuty(S10): Multiple issues,Multiple swags Screen Shot 2015-10-28 at 12.11.04 pm
  10. Hipmunk(S10): Just realized, I was discussing stuff with Steve Huffman 🙂 Screen Shot 2015-10-28 at 12.15.14 pm
  11. Chart.io(S10): Screen Shot 2015-10-28 at 12.20.16 pm
  12. Mailgun(W11): Screen Shot 2015-10-28 at 12.24.17 pm
  13. DR Chrono(W11): Worked with CEO directly and got handsomely rewarded for my work.
  14. Parse(S11):  Yes, Parse CEO said thisScreen Shot 2015-10-28 at 12.33.19 pm
  15. Firebase(S11): Screen Shot 2015-10-28 at 12.36.45 pm
  16. Instacart(S12):   Through private bug bounty
  17. Easel.io(S12):  Acquired by Github, reported multiple issues. Special Thanks page on Github.
  18. Coinbase(S12): Through public bug bounty on Hackerone.
  19. Clever(S12): Screen Shot 2015-10-28 at 12.45.16 pm
  20. Zenefits(W13): Through private Bug bounty.
  21. Heap Analytics(W13): Screen Shot 2015-10-28 at 12.49.59 pm
  22. TrueVault(W14): Screen Shot 2015-10-28 at 12.54.42 pm
  23. Algolia(W14): still have lots of Algolia stickers 🙂
  24. Gitlab(W15): Listed on Acknowledgement page.
  25. Hacker News: Yup, Y Combinator itself. You can find me on their thanks page.

Look like that’s it for now.

so 25, not bad! BTW I am no ninja hacker, most of the stuff are the same task just another website. I have been a jerk professionally (in responding emails), sometimes I didn’t know the tech celebrity I’m talking with, for e.g Steve Huffman, IIya sukar.

I can help with basic web application testing but crowdsourcing your security is the best way to stay updated.

Any questions, suggestions or want to hire me? I’m at bhattacharya.manish7@gmail.com

Logging off


Edit: This list has grown up to 120+, I’m not maintaining this list anymore!

Beginner’s Guide to API(REST) security

API security


API(Application Program Interface) is a framework that makes it easy to build HTTP services that reach a broad range of clients, including browsers and mobile devices. Most of the websites provide API so that developers can make application on top of it. For e.g. Facebook graph API, Twitter API, Dropbox API ,Github API etc .

I’ll discuss few basic points about REST architecture that you need to keep in mind regarding API security.

Authentication: There are various ways to authenticate a user for using your API , most commonly used authentication protocols are HTTP Basic Auth and OAuth.

HTTP Basic Auth : Credentials are merely encoded with Base64, no encryption , no hashing. Every request contain encoded value inside header, so using HTTP Basic Auth without HTTPs is suicide.

OAuth : In this case access token is generated by the resource owner for certain sets of scope . With OAuth, leakage of access token can be dangerous as it contains certain permissions to perform action on behalf of user. Even Facebook was once vulnerable to this,you can read more about this facebook bug in this post.
Authorization is as important as authentication.You must check what are the permissions associated with the access token,Facebook was vulnerable to this as well where hacker can delete any facebook album. Facebook paid him $12,500 for reporting this, read more about this on his  blog.

User Input: There’s a single rule for maintaining security of applications, never trust user input.This apply to API security as well, most of the time web application filter input but they forget to apply filter on input coming from API. Here’s a example of this, Slack was vulnerable to this.
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How to order Free Food in Bangalore

After my Internship , I had  plan to stay in Bangalore for a week. For people who know me I hardly go out alone , problem was going out for lunch  so I thought i’ll order food online .

Dazo is a Bangalore based food ordering app. I had a promo code  DAZO100 for 100rs off on your first order.


One thing I noticed , no traditional account management (registration or OTP verification). I was curious about “how they manage user information”.

In the meantime got a mail from DAZO with order details, but I never entered the mail. Ohh, the app is using my android(google) account.

Adrenaline rush started in my security nerve.

You can create multiple user in Android Lollipop ,


so created a new user (better not mess up with my google settings).This “New user” provide  virtual box like environment, registered with different email,downloaded DAZO , used DAZO100 again and Bang ! .

Had the Chicken for 20 Rs.


DAZO new user acquisition price was rs100 but in my case it was 400+. All you have to do is change the google account from phone setting before placing an order and use DAZO100. Being a tester I have 5,6 gmail and it doesn’t cost anything for creating new.

I came to know that they do verify every order  manually and they know about this 😛 but they don’t have any choice , either fix the bug or deliver the food. I am a  new user with new email , nothing illegal .

They use all sorts of permissions  Device ID,Identity ,WI-FI information and what not.

I had Free food (or paid in 2 figures) for 3 days . I guess now they have fixed it or blocked my phone for code , you can give it a try after all your one email worth INR100.

till then Happy Hacking 🙂


Every CSRF token need not be verified in order to prevent CSRF

Cross-Site Request Forgery (CSRF) is a type of attack that occurs when a malicious Web site, email, blog, instant message, or program causes a user’s Web browser to perform an unwanted action on a trusted site for which the user is currently authenticated. – Wikipedia


I had an interesting encounter with CSRF last week , one of them is yet to be fixed. Here is an interesting low impact issue

These days almost every form on a website use CSRF protection by default. Every time website load  , CSRF token should be different/unique/unpredictable . But this is not the case with 80% of websites out there. I’ll be explaining this two examples one is Dropbox and other is move-app(Facebook)

Let’s start.

Most of the dynamic website contain Sign in functionality as well as forgot password to recover the account.

“Most of the forgot password forms are vulnerable by design , a good practice is to ask a security question before sending reset link” – Aditya

My area of interest was CSRF token for the visitors , public forms like reset password ,sign in ,feedback and all. These tokens are session based (when the site load session started till you close  the browser).

The issue was token remains same for a particular session . For e.g when you submit reset password request first time , token is x, now every time you request areset password  token will be same x.

I thought to abuse this , I made a PHP crawler that will crawl the hidden CSRF value and thought to add token field with my CSRF form . here is the PHP code to extract all the input values from Coinbase.

$doc = new DOMDocument();
$tags = $doc->getElementsByTagName(‘input’);

foreach ($tags as $tag) {
$x= $tag->getAttribute(‘value’).’|’.$tag->nodeValue.”\n”;
echo $x;

I tried to submit my form by scrapped CSRF token ,  badass idea. Didn’t worked , because my page was not creating any session.

Now , the goal was clear I have to use my session to abuse the CSRF. So, what I did is copied my cookie and token and used cookie with document.cookie and token value, this time Bingo !. Continue reading