Is Escaping Single-Quotes in SQL Queries a Reliable Protection Against Injection Attacks?

Defending against SQL injection: Evaluating the effectiveness of data escaping strategies

While parameterized SQL queries are considered the best way to sanitize user input, some developers question the effectiveness of basic input sanitization techniques, such as escaping single quotes and surrounding user input with single quotes.

During the discussion, one developer showed off the code they used for input sanitization:

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

They believe this method eliminates the possibility of SQL injection attacks by preventing users from ending strings and executing other commands. However, some experts warn against using this method because of its inherent flaws.

First, blacklist-based input validation is inherently problematic. A more efficient approach is to define a whitelist of acceptable values ​​and formats to ensure that only valid input is processed.

Research papers on this topic, such as the one at https://www.imperva.com/docs/WP_SQL_Injection_Protection_LK.pdf, provide evidence that even quote escaping can be bypassed, further highlighting the basic input Limitations of cleaning techniques.

Recommended SQL injection prevention methods include:

• Whitelist validation of data type, length, format and acceptable values
• Escape quotes as an add-on to other mitigations
• Query pre-parsing and validation using command and parameter objects
• Only call parameterized queries
• Exclusively use stored procedures to limit SQL execution to predefined commands
• Restrict database permissions to only execute necessary stored procedures
• Implement a comprehensive code base audit to ensure consistent use of secure database access methods

While the technique of escaping single quotes may appear adequate on the surface, it is ultimately unreliable and should be replaced with a more robust and comprehensive security strategy to effectively prevent SQL injection attacks.

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