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Session management is a cornerstone of web security — but when poorly implemented, it can lead to severe exploits like session hijacking. In this post, we examine a critical flaw in a private program related to session token handling that enabled brute-force attacks and unauthorized access to sensitive features.

Before diving into the details, let’s quickly revisit a few foundational concepts:

• A cookie is a small text file stored in your browser by a website, often containing session-related data.
• A session represents a user’s interaction with the website, tracking activity and preserving state.
• A session token (or session ID) is a unique string used to identify a user’s session, enabling continuous interaction without repeated authentication.

When session tokens are poorly implemented — predictable, short, or unprotected — attackers can exploit them through various techniques like brute-forcing, sniffing, or leveraging cross-site scripting (XSS).

During a routine assessment of target.com, a critical flaw was discovered in the API endpoint: