Protection for Man-in-the-Browser (MiTB) attacks

The Man-in-the-Browser (MiTB) attack uses Trojan Horse to intercept and manipulate calls between the browser and its security mechanisms or libraries on-the-fly. The Trojan Horse sniffs or modifies transactions as they are formed on the browser, but still displays back the user's intended transaction. The most common objective of this attack is to cause financial fraud by manipulating transactions of Internet Banking systems, even when other authentication factors are in use.

To protect the user inputs from being attacked by MiTB, FortiWeb implements security rules including obfuscation, encryption, anti-keylogger, and Ajax request white list.


To prevent the MiTB attack from identifying the names of the user input field , FortiWeb obfuscates it into meaningless character strings based on Base64 encoding rule.

For example, for the account name, passwords, and other sensitive user input fields on a transaction page, the obfuscation rule is used to disguise the real values of the input field names.

As shown in the following screenshot, the name of the input field "card 1" is displayed as is in the source code of a transaction page.

After the obfuscation rule is applied to the field name "card 1", the real value is disguised as follows. If the Trojan Horse used by the MiTB attack scans this page for user sensitive data, it won't notice this field because the disguised value is meaningless to it.

See the following topics on how to apply obfuscation to protect the names of the user input fields:


To protect the password that users enter into the web page, FortiWeb encrypts the password from a readable form to an encoded version based on Base64 encoding rule. The encrypted password can only be decoded by FortiWeb.

The following screenshot shows the password (the "secretkey" parameter) without being encrypted.

If the encryption rule is applied to the "secretkey" parameter, its real value will be encrypted, as shown in the following screenshot:

In this case, even if the MiTB attack extracts user data from this package, the secretkey parameter will be useless to the MiTB attack because the real value is encrypted.

See the following topic on how to apply encryption to protect the password input field:


Sometimes the MiTB attack installs a key logger on users' browsers and records each key pressed. Sensitive data such as passwords can be intercepted and recorded, compromising the user account.

If the Anti-Keylogger rule is enabled for the password parameter, FortiWeb prevents it from being recorded even if there is a key logger installed on user's browser.

See the following topic on how to apply anti-keylogger to protect the value of the password input field:

AJAX Request White list

The MiTB attack may use a malicious AJAX worm to hack into the user's browser. It creates an AJAX based sniffer to override the OPEN and SEND function of the AJAX request, and then send the data to a program on a different domain.

FortiWeb supports configuring a white list for AJAX requests. If the user's browser sends AJAX requests to an external domain which is not in the white list, FortiWeb will take action (alert, or alert & deny) according to your configuration.

The following screenshot shows the alert message displayed by FortiWeb when it detects an AJAX request to an external domain not in the white list.


See the following topic on how to add white list for the AJAX request: