Vulnerability

A vulnerability is a weakness or flaw in a computer system, software, hardware, or even a process that can be exploited by an attacker to perform unauthorized actions.

Documentation

See also The Art of PHP - My CTF Journey and Untold Stories! and MAD Bugs: Finding and Exploiting a 21-Year-Old Vulnerability in PHP.

Related : Weak Cryptography, Cross Site Scripting (XSS), Cross Site Request Forgery (CSRF), Man In The Middle, Common Vulnerabilities And Exposures (CVE), Local File Inclusion, Missing Validation, Regexploit, Broken Object Level Authorization (BOLA), Data Leak, Remote Code Execution (RCE), Session Fixation, Attack, Breach, Distributed Denial Of Service (DDOS), Path Traversal, Zero Day Vulnerability, Insecure Deserialization, OWASP, Penetration Test, Timing Attack, Appeasement Pattern