Broken Authentication / Access Control
Broken Authentication - Allows attacker to bypass authentication functions.
Broken Access Control - Allows attackers to access pages and features they should not have access to.
Malicious File Upload
If the web app has a file upload feature and does not properly check and validate uploaded files, attackers can upload a malicious script.
Command Injection
Many web apps execute local OS commands to perform certain processes.
If not properly filtered and sanitized, attackers may be able to inject another command to be executed alongside the originally intended command.
SQL Injection
Web app executes a SQL query including a value taken from user-supplied input.