Fallible Blog Adventures with looking under the hood

Parameters used in scoring for public security dashboard

The following types of bugs were used while ranking startups and their systems for security issues. Almost all of the bugs relate to improper user input validation, lack of proper logic while implementation or not adhering to the principle of least privilege. The weightage were given according to potential impact of the bug, ease of discovery, ease of exploit and requirement of other preconditions if any for exploit. We intend to improve upon this list of parameters and scoring over time.


  1. Oauth redirection issue
  2. OTP refresh/attempts/implementation issue
  3. Destroy all active sessions on reset password (or offer to destroy)
  4. Input validation registration data e.g. javascript:// or data://
  5. Uniqueness constraints in database (account takeover/deletion by replacing email)
  6. Expire session token after logout
  7. Expire password reset links
  8. Session/state fixation
  9. OAuth open redirect in login
  10. OAuth exposed auth token
  11. OAuth fixation attack, missing state or unqiue token
  12. Missing CSRF token auth
  13. Improper UUIDs used as tokens (http://www.ietf.org/rfc/rfc4122.txt)
  14. Invalidate OAuth token during revocation/denial
  15. Exposed Social login tokens in apps
  16. Rate limiting/captcha after retries in reset password

Multiple registration using same unique identifier e.g. mobile

Let’s look at this innocent looking User model that uses mobile number of users as it’s primary key stored in form of string.

class User(db.Model):
	mobile = db.Column(db.String, primary_key=True)
	email = db.Column(db.String(120), unique=True)

Now let’s assume it has to send the mobile number as a big integer to a service that expects mobile numbers to be big integers for sending OTPs.

func sendMessage(mobileNumber: Int64, message: String) -> Bool {
    return true

func sendOTP(mobileNumber: Int64) -> Bool {
    let OTP = 1000 + arc4random_uniform(8999)
    let text = "Your OTP is \(OTP) and is valid for 15 minutes"
    return sendMessage(mobileNumber, message: text)

What is wrong here? Maybe the code below will clear things up. This is what happens in Python when you try converting a string to integer.

>>> phone_no = "7007001234"
>>> phone_no_evil = "7007001234\n\n"
>>> int(phone_no) == int(phone_no_evil)
>>> phone_no == phone_no_evil

And, this is what happens when you try it in Swift

Screen Shot 2016-01-31 at 2.30.24 AM.png


Secure HTTP Headers (X-XSS-Protection, X-FRAME-Options, HSTS, CSP)

The web was created to serve static pages of content. People did not think about security for all the additional features we added to it. With these features, came security issue and there have been improvements and fixes. Just use them. It is still surprising that your servers do not have these HTTP headers.

  • Secure, httponly cookies
  • SPF headers for main and marketing email domains
  • Dangling subdomain based takeover
  • SSL configuration based issues
  • Sensitive cookies without secure flag set
  • Directory traversal
  • AWS S3 buckets exposed

Credit card details or sensitive information over HTTP

It’s 2016 and yet a billion dollar startup takes credit card information for one of their products over HTTP! Dont do it. MITM attack are really easy, just go to your nearby coffee shop or Airport.

Exposed backup files over public network

We found a machine where someone had redirect stdout of history command to a file and it was exposed online. The file has a command where a login to a remote mysql server was being done using password. In another case, we found sql dumps of databases neatly stored under a directory called backups arranged by months and date.

  • File disclousure
  • Subresource Integrity
  • Public Key Pinning


  • Secret token leak in apps/API
  • Poor SDK implementation

Poor design choices

This was an actual bug we discovered in a billion dollar startup. You could pay for an order of amount X and then use the same payment id to associate it with other future orders, the only condition being that the new order amount has to be the same as specified in the payment id. This bug could allow you to place orders for the same amount multiple number of times and pay just once. Notice that there is no unique constraint on payment_id in Transaction model.

class Order(db.Model):
	id = db.Column(db.Integer, primary_key=True)
	amount = db.Column(db.Float)

class Transaction(db.Model):
	id = db.Column(db.Integer, primary_key=True)
	order_id = db.Column(db.Integer, db.ForeignKey('order.id'), unique=True)
	payment_id = db.Column(db.Integer, db.ForeignKey('paymentgateway.id'))

class PaymentGateway(db.Model):
	id = db.Column(db.Integer, primary_key=True)
	amount = db.Column(db.Float)
  • Weak salt /secret strength of provider
  • Server side data integrity verification for payment requests
  • Race condition in coupon redemption
  • Weak emunerable coupons
  • Poorly designed referral system

Authoriation & Personal data

  1. Account details leak, missing authorization token
  2. Project more data than required in API responses
  3. Order History/information leak other than personal details
  4. Working Authorization token (not only mere presence)

Other attacks

  1. CSRF/secure token expose over HTTP (possible MITM attack)
  2. CRLF Injection attack
  3. SQL Injection
  4. XSS
  5. SQL injection using cookies
  6. CSRF token checks
  7. Open Redirects
  8. CSV Excel macro injection
  9. Server side request forgery (a good writeup here)
  10. XXE /JSON based injection