This question describes a classic example of Tautology-Based SQL Injection, a subcategory of SQL Injection attacks which fall under Web Application Hacking in the CEH curriculum.
In a tautology-based SQL injection, the attacker injects a SQL fragment that always evaluates to true, thus bypassing the authentication mechanism. The string ' C 'll-T; — is a malformed variant, possibly meant to represent ' OR '1'='1'; --, which is one of the most basic and widely recognized tautology-based injection payloads. When injected into a vulnerable SQL query, this kind of input manipulates the WHERE clause of the query so that it always evaluates to true, regardless of the original conditions.
Here’s how it works:
If the SQL query is:
SELECT * FROM users WHERE username = '$username' AND password = '$password';
And the attacker inputs:
' OR '1'='1'; --
The query becomes:
SELECT * FROM users WHERE username = '' OR '1'='1'; --' AND password = '';
This results in the execution of:
SELECT * FROM users WHERE '1'='1';
Which always evaluates to true, thereby bypassing authentication and allowing unauthorized access.
This method does not rely on error messages (Error-Based), timing delays (Time-Based Blind), or UNION statements (Union-Based). Its goal is to exploit logic within the query structure itself using boolean-based manipulation.
According to EC-Council's CEH v13 Module: Web Application Hacking, understanding tautology-based injection is critical because it's one of the most common ways attackers bypass login forms on poorly secured web applications.
