Description

The Web Parameter Tampering attack is based on manipulation of parameters exchanged between client and server in order to modify application data such as user credentials and permissions, price and quantity of products, etc. Usually, this information is stored in cookies, hidden form fields or URL Query Strings and is used to increase application functionality and control.

This attack can be performed in the context of a malicious user who wants to exploit the application for their own benefit or an attacker who wishes to attack a third-person using a Man in the Middle attack. In both cases, tools likes Webscarab and Paros proxy are mostly used.

The attack success depends on integrity and logic validation mechanism errors and its exploitation can result on other consequences including XSS, SQL Injection, file inclusion and path disclosure attacks.

Severity

High

Likelihood of exploitation

Very High

Examples

Example 1

The parameter modification of form fields can be considered a typical example of Web Parameter Tampering attack.

For example, consider a user who can select form field values (combo box, check box, etc.) on an application page. When these values are submitted by user, they could be acquired and arbitrarily manipulated by an attacker.

Example 2

When a web application uses hidden fields to store status information, a malicious user can tamper the values stored on his browser and change the referred information. For example, an e-commerce shopping site uses hidden fields to refer to its items, as follows:

<input type=”hidden” id=”1008” name=”cost” value=”70.00”>

In this example, an attacker can modify the “value” information of a specific item, thus lowering its cost.

Example 3

An attacker can tamper URL parameters directly. For example, consider a web application that permits user to select his profile from a combo box and debit the account:

http://www.attackbank.com/default.asp?profile=741&debit=1000

In this case, an attacker could tamper the URL using other values for profile and debit:

http://www.attackbank.com/default.asp?profile=852&debit=2000

Other parameters can be changed including attribute parameters. In the following example, it’s possible to tamper the status variable and delete a page from the server:

http://www.attackbank.com/savepage.asp?nr=147&status=read

Modifying status variable to delete the page:

http://www.attackbank.com/savepage.asp?nr=147&status=del