[Solved] Consider a login system using this vulnerable query:SELECT * FROM users WHERE username = '" + userInput + "' AND password = '" + passInput + "';If an attacker inputs admin' -- as username and... | SQL

SQL - Security Basics

Consider a login system using this vulnerable query:
SELECT * FROM users WHERE username = '" + userInput + "' AND password = '" + passInput + "';
If an attacker inputs admin' -- as username and anything as password, what happens and why?

ALogin succeeds without password check because -- comments out rest

BLogin fails due to syntax error from unmatched quotes

CLogin succeeds only if password matches exactly

DLogin fails because input is rejected by the system

Step-by-Step Solution

Solution:

Step 1: Substitute attacker input into query
The query becomes: SELECT * FROM users WHERE username = 'admin' --' AND password = 'anything';
Step 2: Understand effect of -- comment
The -- makes the rest of the query a comment, so password check is ignored.
Step 3: Result of query
The query checks only username = 'admin', allowing login without password.
Final Answer:
Login succeeds without password check because -- comments out rest -> Option A
Quick Check:
-- comments out password check = Login bypass [OK]

Quick Trick: SQL comment -- skips password check for login bypass [OK]

Common Mistakes:

Assuming syntax error occurs
Thinking password is still checked
Believing input is blocked automatically

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More SQL Quizzes

Consider a login system using this vulnerable query:

Step 1: Substitute attacker input into query

Step 2: Understand effect of -- comment

Step 3: Result of query

Final Answer:

Quick Check:

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