Testing for weak password change or reset functionalities (OTG-AUTHN-009)

Summary
The password change/reset function of an application is a self-service password change/reset mechanism for users. This self-service mechanism allows users to quickly change/reset their password without an administrator intervening. When passwords are changed they are typically changed within the application. When passwords are reset they are either rendered within the application or emailed to the user. This may indicate that the passwords are stored in plaintext or in a decryptable format.

Test objectives
Determine the resistance of the application to subversion of the account change process allowing someone to change the password of an account. Determine the resistance of the passwords reset functionality against guessing or bypassing.

Black Box Testing and Examples
For both functionalities (password change and password reset) it is important to check:
 * 1) if users, other than administrators, can change/reset passwords for accounts other than their own.
 * 2) if users can manipulate/subvert the password change/reset process to change/reset the password of another user or administrator.
 * 3) if the password change/reset process is vulnerable to CSRF

Test Password Reset
In addition to the previous checks it is important to verify the following:

The first step is to check whether secret questions/information are required. Sending the password (or a password reset link) to the user email address without first asking for a secret question means relying 100% on the security of that email address, which is not suitable if the application needs a high level of security. On the other hand, if secret questions are used, the next step is to assess their strength. This specific test is discussed in detail in the Testing for Weak security question/answer paragraph of this guide. The most insecure scenario here is if the password reset tool shows you the password; this gives the attacker the ability to log into the account, and unless the application provides information about the last login the victim would not know that his/her account has been compromised. A less insecure scenario is if the password reset tool forces the user to immediately change his/her password. While not as stealthy as the first case, it allows the attacker to gain access and locks the real user out. The best security is achieved if the password reset is done via an email to the address the user initially registered with, or some other email address; this forces the attacker to not only guess at which email account the password reset was sent to (unless the application show this information) but also to compromise that email account in order to obtain the temporary password or the password reset link. The most insecure scenario here is if the application sends/visualizes the old password in clear text because this means that passwords are not stored in a hashed form, which is a security issue in itself. The best security is achieved if passwords are randomly generated with a secure algorithm that cannot be derived. To limit denial-of-service attacks the application should send, via e-mail, a link to the user with a random token, and only if the user visits the link then the reset procedure is completed. This ensures that the current password will still be valid until the reset has been confirmed.
 * What information is required to reset the password?
 * How are reset passwords communicated to the user?
 * Are reset passwords generated randomly or not?
 * Is the reset password functionality requesting confirmation before changing the password?

Test Password Change
In addition to the previous test it is important to verify:

The most insecure scenario here is if the application permits the change of the password without requesting the current password. Indeed if an attacker is able to take control of a valid session (s)he could easily change the victim's password.
 * Is the old password requested to complete the change?

See also Testing for Weak password policy paragraph of this guide.

Remediation
The password change/reset function is a sensitive function and requires some form of protection, such as requiring users to re-authenticate or presenting the user with confirmation dialogs during the process.