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In the development of authentication systems, it is common for novice engineers to make mistakes that compromise the security of the application. When building a system with JWT tokens (access and refresh) for session management, vulnerabilities can appear that go unnoticed in basic tests but expose the infrastructure to real attacks. Below, we analyze four critical flaws —SQL injection, email enumeration, password comparison, and non-revocable tokens— and how to fix them, with a practical approach that every development company should implement.
The first error, SQL injection, occurs when building queries by directly concatenating user input. An attacker can modify a URL parameter, for example ?id=10 OR (1=1), and obtain all records from the database. The standard solution is to use parameterized queries, where the value is treated as data and not as SQL code. Additionally, tools like ORMs or input validation reinforce security. In a comprehensive cybersecurity strategy, it is essential to combine these practices with periodic audits and pentesting, something we offer at Q2BSTUDIO to protect custom applications against this type of vector.
The second flaw is email enumeration, which occurs when the API returns different messages for "email not found" and "incorrect password". An attacker can launch a brute force attack against the login endpoint and, based on the responses, identify valid addresses. The solution is to unify the error message: always respond with "Invalid credentials". This approach is part of the good cybersecurity practices that we apply in our custom software projects.
The third problem is password comparison using the === operator. This method is vulnerable to timing attacks, because the string comparison algorithm stops at the first difference. With thousands of attempts, an attacker can deduce the password character by character by measuring the response time. The fix is to use bcrypt.compare(), which uses constant-time comparison and also stores the hash with an appropriate cost factor. At Q2BSTUDIO we integrate these techniques in all our developments, ensuring that custom applications handle credentials securely.
The fourth error is issuing refresh tokens without storing them, which prevents revoking them in case of theft or logout. A pure JWT token is immutable until its expiration; if an attacker intercepts it, they have access for days. The solution is to save the token in an external storage like Redis, with a TTL (time-to-live) that matches the token's duration. When logging out, the Redis entry is deleted, rendering the token useless. This managed session logic is key in systems that require high availability and access control, like those we develop with cloud services aws and azure.
Beyond these flaws, modern authentication architecture must rely on additional tools: rate limiting, security headers with helmet.js, and the use of AI agents to detect anomalous patterns in real time. Artificial intelligence for businesses can analyze millions of requests and block intrusion attempts before they cause damage. For example, AI agents integrated into Power BI dashboards allow visualizing threats and generating automatic alerts. At Q2BSTUDIO we offer business intelligence services that connect security with analytics, helping organizations make informed decisions. Additionally, we combine ai for businesses with custom applications to create robust and scalable solutions.
The conclusion is clear: these four errors are not detected in basic functional tests, but only when an attacker tries to exploit them. Reviewing the OWASP Top 10 after having written vulnerable code is a lesson that transforms the way you think about security. At Q2BSTUDIO, we understand that each project requires a personalized approach; that is why we accompany our clients from the design phase to deployment, integrating custom software with the best cybersecurity practices and cloud services aws and azure. Building a secure authentication system not only protects user data, but also strengthens trust in the brand.
