A2: Broken Authentication
App Specific
Attackers have access to hundreds of millions of valid username and password combinations for credential stuffing, default administrative account lists, automated brute force, and dictionary attack tools.
Session management attacks are well understood, particularly in relation to unexpired session tokens.
Prevalence
The prevalence of broken authentication is widespread due to the design and implementation of most identity and access controls. Session management is the bedrock of authentication and access controls, and is present in all stateful applications.
Attackers can detect broken authentication using manual means and exploit them using automated tools with password lists and dictionary attacks.
Technical
Attackers have to gain access to only a few accounts, or just one admin account to compromise the system. Depending on the domain of the application, this may allow money laundering, social security fraud, and identity theft, or disclose legally protected highly sensitive information.
Confirmation of the user's identity, authentication, and session management are critical to protect against authentication-related attacks. There may be authentication weaknesses if the application:
Permits automated attacks such as credential stuffing, where the attacker has a list of valid usernames and passwords.
Permits brute force or other automated attacks.
Permits default, weak, or well-known passwords, such as "Password1" or "admin/admin"
Uses weak or ineffective credential recovery and forgot password processes, such as "knowledge-based answers", which cannot be made safe.
Uses plain text, encrypted, or weakly hashed passwords (see A3:2017-Sensitive Data Exposure).
Has missing or ineffective multi-factor authentication.
Exposes Session IDs in the URL (e.g., URL rewriting).
Does not rotate Session IDs after successful login
Does not properly invalidate Session IDs. User sessions or authentication tokens (particularly single sign-on (SSO) tokens) aren't properly invalidated during logout or a period of inactivity.
