OWASP Top 10 is a ranked list of the most dangerous web application security flaws, published by the Open Web Application Security Project. The current list (2021) includes: broken access control, cryptographic failures, injection attacks (SQL, OS, LDAP), broken authentication, insecure deserialization, XML external entities, broken access control, using components with known vulnerabilities, insufficient logging and monitoring, and server-side request forgery. Each flaw describes the attack method, impact if exploited, and prevention strategies. Unlike theoretical security knowledge, OWASP Top 10 is grounded in real-world breaches—the list is updated every 3-4 years based on which vulnerabilities are actually being exploited at scale.