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 #3, ).

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

The Auth part was of this section was had an interesting bug.

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 will 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 and I got blocked by the 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.
Continue reading

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.
Continue reading

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. 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.  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

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.
Continue reading

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

How I made $2000 in 15 minutes

When I am not hunting I read about startups ,what’s happening in valley. I check their site , as a security guy I cannot control myself from checking their security. In the process , I came across this accounting web application (they are quite famous and making big bucks, I won’t take the name as they might get disturbed after this post. ) I was just testing for common bug XSS,CSRF and all regular stuff. 55013960   Every field was vulnerable to XSS and every form was vulnerable to CSRF as  token was not validating . Used Contact Us section from the site. Some non-technical lady replied “Thanks for contacting us , we don’t have any reward scheme or anything” .   55014089     Let’s give it one more try, this time I used About US page, googled the name of the engineer , found his Github  account and found his gmail there. He was really nice to me. test       Later we had Video chat on Skype , he was explaining me things ,asking me about my background.He was impressed. Following is a copy paste from the original POC that I sent back then   1. XSS:- javascript is not  filtered ,hence any arbitrary javascript code can be executed. Hence with document.cookie , a user’s cookie can be stolen ,that can lead to full account take over. Continue reading

An Introduction to SEO

Last week , We had our first company campus drive of the season. We all were excited. There were 3 job profiles , one of them were SEO executive. I had some know how of SEO , I was confident enough to grab this position because  my site has google page rank 5 and  I have  a “Certificate of Honor” in SEO


I was like:


Although I got the Offer letter


but they made me uncomfortable during the interview so I thought let’s get prepared , here is some of the basic things you should know about SEO as internet user.

SEO stands for Search Engine Optimization . SEO are the techniques one use to get his site on top in a search result. If your is on top in  search result, users are more interested in visiting those top sites that means more traffic ,more user and more money.

For example: when you do a search for Manish Bhattacharya ,you will see something like this

testThe search result bring my site on the top , although there are other sites which have my information but my site is on top ,hence you if have to know more about me you will visit my site rather than visiting other random sites.

Now how SEO is done ? SEO require some optimization in code and contents. You should be aware of Keywords ,in last example Manish Bhattacharya was the keywords. Keywords are stream of words user search on search engine (google). You should be aware on what keywords you are focusing , suppose if you have selling mobiles phone in Delhi, so your keywords should be strong enough to pop up your site when user search for “Mobile phone store in Delhi”.

Other determining factors are your domain name, your site’s title and meta descriptions. Meta descriptions are information about the site that you see in search results. Here it is :


Meta descriptions and keywords can be added using Meta tag , inside <Head> after <title> like this


One of the questions I remember from the interview was the maximum length of Meta descriptions and keywords.In general maximum sizes are

  • Page Title – 70 characters
  • Meta description – 160 characters
  • Meta keywords – No more than 10 keyword phrases

SEO does not end here , your URL structures for e.g. default URL setting for any wordpress site is like php?id= some post id , a url with content descriptions is suggested for better SEO something like this “; ,make your site easy to navigate , a better robots.txt and site map really helps a lot.

Also optimize your anchor tag and image tag, using title and alt in <img is suggested for better SEO. Using Heading(<h1>,<h2>…) Tag properly is a plus.

Other questions that I remember was “Types of SEO and what are Panda,Penguin,EMD “.

There are two types of SEO:

  1. White Hat
  2. Black Hat

White hat are the techniques that are suggested by the search engines to improve your page ranking while black hat are techniques that use weakness of ranking algorithm to rank them on the top.You can read more on this here.

Humming Bird,Panda ,Penguin,Venice and EMD are the names of Google search result algorithms .

There are other terms that you should know about SEM(search engine marketing),PPC (pay per click) and more. Hope I’ll share more with you on this. Here’s some suggested further reading if you are interested:

  3. search-engine-optimization-starter-guide

This is just an introduction , SEO jobs are high paying even SEO experts makes millions just by freelancing.Neil patel ,Hiten Shah are some well known name in this business.

logging off..