Filtering Unsafe Characters for SQL Injection Prevention Quiz

Enhance your understanding of filtering unsafe characters in user inputs to protect against SQL injection in security testing. This quiz evaluates your ability to identify risky input patterns, effective validation methods, and common pitfalls when handling user-submitted data in database contexts.

1. Recognizing Dangerous Input Patterns

   Which user input is most likely to facilitate a basic SQL injection if not properly filtered: username='admin' OR '1'='1'?

   1. username=admin123
   2. username=admin'--
   3. username='admin' OR '1'='1'
   4. username=Robert); DROP TABLE Students;--

   Explanation: The input username='admin' OR '1'='1' is a classic example of an SQL injection attempt, manipulating logic within a query. Option D represents a more advanced injection but does not directly match the technique described. Option B only introduces a comment symbol, and Option A is a safe, regular input. Focusing on filtering logical operators and quotation marks is crucial to preventing such attacks.

2. Best Practice for Filtering

   What is the most effective way to prevent SQL injection when handling user input for database queries?

   1. Sanitizing input by removing HTML tags only
   2. Using parameterized queries (prepared statements)
   3. Filtering input to exclude all spaces
   4. Limiting input length to 15 characters

   Explanation: Parameterized queries (prepared statements) ensure that user input is treated as data, not executable code, which makes them the most effective method for preventing SQL injection. Simply removing HTML tags does not prevent SQL injection. Filtering out spaces or limiting input length might reduce attack vectors but will not eliminate the core risk. These approaches are insufficient compared to prepared statements.

3. Unsafe Character Identification

   Which of the following user input characters is commonly considered unsafe and should be handled carefully to prevent SQL injection?

   1. Semicolon (;)
   2. At symbol (@)
   3. Hash (#)
   4. Percent sign (%)

   Explanation: The semicolon is used to terminate SQL statements, allowing attackers to append malicious queries, so it is particularly dangerous in user input. The at symbol and percent sign are typically safe in most contexts, but the hash symbol can introduce comments in some SQL engines. However, the semicolon more directly facilitates injection, making it the correct focus.

4. Limitations of Input Validation

   Why is relying solely on client-side filtering of unsafe characters insufficient to defend against SQL injection?

   1. Because client-side validation does not check data formats
   2. Because attackers can bypass or disable client-side controls
   3. Because client-side filtering prevents cross-site scripting
   4. Because client-side validation cannot remove digits

   Explanation: Client-side defenses can be bypassed by submitting HTTP requests directly or disabling scripts, so server-side validation is always required. Data format checking and input length do not address the core issue of bypassing client rules. Client-side efforts do not reliably prevent SQL injection or cross-site scripting on their own.

5. Whitelist vs. Blacklist Filtering

   When validating user input to prevent SQL injection, what is the primary advantage of using a whitelist approach over a blacklist?

   1. A whitelist allows more flexible user input
   2. A whitelist defines exactly what is permitted, making it harder for unsafe characters to slip through
   3. A whitelist is easier to maintain
   4. A whitelist works better with legacy databases

   Explanation: Whitelisting specifies the only acceptable input formats or values, reducing the risk of attackers finding unanticipated ways to inject malicious input. Allowing more flexible input or easier maintenance might actually weaken security. Compatibility with legacy systems is unrelated; the main benefit is stronger control over accepted input.