Application security involves securing software from attack vectors like code execution, buffer overflows, SQL injection, cross-site scripting, cryptography weaknesses, and business logic errors. Common attacks exploit vulnerabilities like injecting SQL commands, executing JavaScript in privileged contexts, or making authorized systems behave unexpectedly. Preventive actions include thorough code reviews, staying up-to-date on patches, reacting quickly to incidents, and having controls like firewalls and deployment strategies that limit impact.