DataStructures / System Design
What is SQL injection?
SQL injection is the highest application security concern because it's well known, easy to perform and operates on the database server.
SQL injection occurs when:
- Malicious data is used to construct SQL statements via string concatenation, thus commingling executable code and data.
- Executable code and data are commingled; the database server parsing the query may interpret the "data" as executable code/query. This allows the data to alter the meaning/result of the SQL query.
- A single attack can leak an entire database, alter or destroy a database, or even lead to a compromise of the server where the database is deployed.
To mitigate the SQL injection risk:
- Use parameterized queries with bind variables to ensure that data added to the statement cannot alter the intention of the statement.
- Validate untrusted data; data submitted by end users.
SQL Injection example:
In the following code $user_name and $password represent variable for user input, which are then used to create a SQL statement.
SELECT * FROM BankAccounts WHERE username=$user_name AND password = $password;
A malicious user may provide input which bypasses the intended functionality of the query and which actually grants unlimited access, just by simply commenting out the "AND" portion of the SQL statement.
SELECT * FROM BankAccounts WHERE username='admin'--'AND password = 'password123';
Notice the comment indicator (--) after the username. The database will interpret the rest of the query as a comment, ignoring the password verification. The effective statement that gets executed is:
SELECT * FROM BankAccounts WHERE username='admin'
The attacker who submitted that login attempt would be granted access to resources owned by the "admin" account.
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