Is Escaping Single Quotes a Reliable Defense Against SQL Injection?

SQL injection protection: the fallacy of single quote escaping

In the field of software development, preventing SQL injection attacks is crucial. Although parameterized SQL queries are the best method for input sanitization, some developers still resort to escaping single quotes and wrapping user input in single quotes as an alternative defense mechanism.

Flawed escaping techniques

The method consists of replacing any single quotes in the user input with double single quotes and enclosing the entire string in single quotes:

<code>sSanitizedInput = "'" & Replace(sInput, "'", "''") & "'"</code>

The idea behind this technique is that any single quotes entered by the user are effectively neutralized, preventing string termination. Therefore, any other characters, such as semicolons or percent signs, become part of the string and are not executed as commands.

Injection vulnerability

However, this technique cannot handle situations where the user input itself may contain double single quotes. In this case, the string is terminated and the remaining input can be executed as an SQL command.

Example input

To illustrate this, consider the following user input:

<code>'SensitiveData' HAVING AMOUNT>2000 OR ''=''</code>

After execution, the code will become:

<code>SELECT * FROM ACCOUNT WHERE NAME='SensitiveData' HAVING AMOUNT>2000 OR ''=''</code>

This input successfully injects an OR clause into the SQL query, bypassing the intended sanitization.

Further considerations

It is important to note that this escaping technique has other vulnerabilities, including:

• Does not protect against all types of SQL injection attacks, such as those using comments or other statement terminators.
• Introduces performance and maintenance overhead.
• Making the code difficult to read and understand.

Best Practices

Do not rely on ad-hoc input sanitization techniques, follow these best practices to prevent SQL injection:

• Use parameterized SQL queries or JDBC prepared statements.
• Only allow expected input values ​​and formats (whitelist).
• Use blacklists only when absolutely necessary and after implementing additional mitigation measures.
• Avoid dynamic SQL and string concatenation.
• Consider using stored procedures with limited database permissions.

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