Testing for Vulnerable Remember Password (OWASP-AT-006)

Summary
Browsers will sometimes ask a user if they wish to remember the password that they just entered. The browser will then store the password, and automatically enter it whenever the same authentication form is visited. This is a convenience for the user.

Description of the Issue
Having the browser storing passwords is not only a convenience for end-users, but also for an attacker. If an attacker can gain access to the victim's browser (e.g. through a Cross Site Scripting attack, or through a shared computer), then they can retrieve the stored passwords. It is not uncommon for browsers to store these passwords in an easily retrievable manner, but even if the browser were to store the passwords encrypted and only retrievable through the use of a master password, an attacker could retrieve the password by visiting the target web application's authentication form, entering the victim's username, and letting the browser to enter the password.

Black Box testing and example

 * Enter a username and password in the target authentication form and determine whether the browser asks the user whether they want the password remembered.
 * View the authentication form's HTML source code and look for the autocomplete="off" attribute in the password form field. The code for this may resemble the following:
 * Look for passwords being stored in a cookie. Examine the cookies stored by the application. Verify that the credentials are not stored in clear text, but are hashed. Examine the hashing mechanism: if it is a common, well-known algorithm, check for its strength; in homegrown hash functions, attempt several usernames to check whether the hash function is easily guessable. Additionally, verify that the credentials are only sent during the login phase, and not sent together with every request to the application.
 * Look for other areas where a password may be entered (and hence be remembered by the browser), e.g. a change password form.
 * Consider other sensitive form fields (e.g. an answer to a secret question that must be entered in a password recovery or account unlock form).

Remediation
Any fields that contain sensitive information and passwords should be flagged in the HTML source code with AUTOCOMPLETE=”off”. Moreover no credentials should to be stored in clear text in cookies.