OWASP API Top 10:2023 – Broken Authentication and the Weak Link in API Security
In modern digital architectures, APIs form the backbone of applications. From mobile apps to microservice-based systems, APIs offer speed and flexibility—but they also introduce serious security risks. To help assess and prioritize these risks, the OWASP API Top 10 list serves as a vital reference for developers and security professionals alike. Ranked second on the 2023 list, “Broken Authentication” stands out as one of the most dangerous—and often overlooked—vulnerabilities.
Broken Authentication refers to faulty or missing authentication mechanisms within APIs. Any weakness in a system’s ability to correctly verify a user’s identity can provide attackers with direct access. This vulnerability commonly arises from poor token validation, the use of predictable or non-expiring session credentials, JWTs signed with insecure algorithms, or exposed authentication endpoints in production environments. Additionally, improperly handled session terminations can significantly amplify the risk.
What makes Broken Authentication so critical is that it doesn’t require advanced hacking techniques. Attackers can often gain access without breaking a sweat. For instance, a valid token captured from a mobile app could allow an attacker to access sensitive user data. A non-expiring JWT might keep a session alive indefinitely, or a system that doesn’t properly verify token expiration could allow an old token to be reused. In some cases, sensitive endpoints might even be accessible without any token at all.
So, is it possible to defend against such a threat? Absolutely—but it requires a careful and comprehensive approach. First and foremost, authentication processes must be consistently enforced across all API requests. Access tokens should be short-lived, and refresh tokens should be implemented where necessary. Adding multi-factor authentication (MFA) further strengthens the system.
Session management is another critical component. When a user logs out, their session must truly end. Token reuse must be prevented, and all flows related to token expiration, renewal, and revocation must be clearly defined. When using JWTs, secure algorithms such as RS256 should be chosen over insecure options like alg: none, and fields such as issuer and audience must be strictly validated.
One of the most effective steps development teams can take is to test their systems as if they were attackers. Try sending requests without tokens, reusing expired or tampered tokens, or scanning for exposed authentication endpoints in production. These tests can be carried out manually or with tools such as Burp Suite, Apistrike, or similar automated platforms.
Always remember: authentication is not just about a login form. It’s a system-wide responsibility, and attackers will always look for the weakest link. When designing or testing your APIs, make it a habit to ask, “Where is the weakest point?” The OWASP API Top 10 list is a powerful compass on that journey. In the next post of this series, we’ll examine another critical risk highlighted by that list.
