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Business Logic Errors.md

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Business Logic Errors

Introduction

Business Logic Errors are ways of using the legitimate processing flow of an application in a way that results in a negative consequence to the organization.

Where to find

This vulnerability can appear in all features of the application.

How to exploit

  1. Review Functionality

    • Some applications have an option where verified reviews are marked with some tick or it's mentioned. Try to see if you can post a review as a Verified Reviewer without purchasing that product.
    • Some app provides you with an option to provide a rating on a scale of 1 to 5, try to go beyond/below the scale-like provide 0 or 6 or -ve.
    • Try to see if the same user can post multiple ratings for a product. This is an interesting endpoint to check for Race Conditions.
    • Try to see if the file upload field is allowing any exts, it's often observed that the devs miss out on implementing protections on such endpoints.
    • Try to post reviews like some other users.
    • Try performing CSRF on this functionality, often is not protected by tokens

  2. Coupon Code Functionality

    • Apply the same code more than once to see if the coupon code is reusable.
    • If the coupon code is uniquely usable, try testing for Race Condition on this function by using the same code for two accounts at a parallel time.
    • Try Mass Assignment or HTTP Parameter Pollution to see if you can add multiple coupon codes while the application only accepts one code from the Client Side.
    • Try performing attacks that are caused by missing input sanitization such as XSS, SQLi, etc. on this field
    • Try adding discount codes on the products which are not covered under discounted items by tampering with the request on the server-side.

  3. Delivery Charges Abuse

    • Try tampering with the delivery charge rates to -ve values to see if the final amount can be reduced.
    • Try checking for the free delivery by tampering with the params.

  4. Currency Arbitrage

    • Pay in 1 currency say USD and try to get a refund in EUR. Due to the diff in conversion rates, it might be possible to gain more amount.

  5. Premium Feature Abuse

    • Try forcefully browsing the areas or some particular endpoints which come under premium accounts.
    • Pay for a premium feature and cancel your subscription. If you get a refund but the feature is still usable, it's a monetary impact issue.
    • Some applications use true-false request/response values to validate if a user is having access to premium features or not.
    • Try using Burp's Match & Replace to see if you can replace these values whenever you browse the app & access the premium features.
    • Always check cookies or local storage to see if any variable is checking if the user should have access to premium features or not.

  6. Refund Feature Abuse

    • Purchase a product (usually some subscription) and ask for a refund to see if the feature is still accessible.
    • Try for currency arbitrage explained yesterday.
    • Try making multiple requests for subscription cancellation (race conditions) to see if you can get multiple refunds.

  7. Cart/Wishlist Abuse

    • Add a product in negative quantity with other products in positive quantity to balance the amount.
    • Add a product in more than the available quantity.
    • Try to see when you add a product to your wishlist and move it to a cart if it is possible to move it to some other user's cart or delete it from there.

  8. Thread Comment Functionality

    • Unlimited Comments on a thread
    • Suppose a user can comment only once, try race conditions here to see if multiple comments are possible.
    • Suppose there is an option: comment by the verified user (or some privileged user) try to tamper with various parameters in order to see if you can do this activity.
    • Try posting comments impersonating some other users.

  9. Parameter Tampering

    • Tamper Payment or Critical Fields to manipulate their values
    • Add multiple fields or unexpected fields by abusing HTTP Parameter Pollution & Mass Assignment
    • Response Manipulation to bypass certain restrictions such as 2FA Bypass

References