SQL Injection.

Sql Injection Is A Type Of Attack That Occurs When A Malicious User Inserts Sql Code Into A Web Form Input Or Url Query String In Order To Manipulate The Database And Retrieve Sensitive Information. 

Here Is An Example Of How Sql Injection Works:

Suppose A Website Has A Login Form That Accepts A Username And Password. The Website's Backend Database Stores The Username And Password Information In A Table Called "Users". The Sql Statement Used To Check The User's Login Credentials Might Look Like This:

```

Select * From Users Where Username = 'input_Username' And Password = 'input_Password'

```

A Malicious User Can Insert Sql Code Into The Login Form Input, Such As:

```

' Or 1=1 --

```

This Code Will Be Concatenated With The Original Sql Statement And Cause The Database To Retrieve All Records From The "Users" Table, Because The "Or 1=1" Condition Is Always True. The Double Dash (--) Signifies A Comment, Which Comments Out The Remainder Of The Original Sql Statement. So The Final Sql Statement Executed By The Database Becomes:

```

Select * From Users Where Username = '' Or 1=1 --' And Password = 'input_Password'

```

This Allows The Attacker To Bypass The Login Credentials And Gain Unauthorized Access To The System.

Sql Injection Attacks Can Be Prevented By Using Prepared Statements Or Parameterized Queries, Which Ensure That Input Is Properly Sanitized And Validated Before Being Used In Sql Statements. Additionally, Database Users Should Avoid Using Dynamic Sql Queries Whenever Possible, And Should Limit The Privileges Granted To Web Applications To Only What Is Necessary For Them To Function. Regular Security Audits And Penetration Testing Can Also Help To Identify And Prevent Sql Injection Vulnerabilities.