OWASP - SQL Comment Sequence Detected

Introduction

• A “SQL comment sequence detected” warning typically indicates that user input might contain SQL comment sequences, which could potentially be used for SQL injection attacks.
• In SQL, comments can be introduced using – for single-line comments and /* … */ for multi-line comments.
• An attacker might try to inject SQL comment sequences to manipulate SQL queries.

Understanding SQL Injection and Comment Sequences

• SQL injection is a common attack vector where an attacker can execute arbitrary SQL code on the database by injecting malicious input into a query.
• Comments are often used in SQL injection attacks to terminate a legitimate SQL query prematurely and append malicious SQL code.

Example of SQL Injection with Comments

• An attacker might input something like this:

  ' OR '1'='1' -- 
  

• In a poorly constructed SQL query, this could transform a query like:

  SELECT * FROM users WHERE username = 'admin' AND password = 'password';
  

  Into something like:

SELECT * FROM users WHERE username = 'admin' OR '1'='1' -- ' AND password = 'password';

• This changes the logic of the query and can result in unauthorized access.

How to Handle SQL Comment Sequences

• Input Sanitization: Always sanitize and validate user inputs to ensure they do not contain any harmful sequences.
• Parameterized Queries: Use parameterized queries or prepared statements. These ensure that user input is treated as data rather than executable code.
• ORM Usage: Use an Object-Relational Mapping (ORM) library, which typically handles SQL injection prevention mechanisms internally.
• Database Permissions: Ensure that your database user accounts have the minimal necessary permissions to reduce the impact of any potential SQL injection attacks.

Example with Parameterized Queries

• Here’s an example using Python’s sqlite3 module with parameterized queries to prevent SQL injection:

import sqlite3

# Connect to the database
conn = sqlite3.connect('example.db')
cursor = conn.cursor()

# User input
username = input("Enter username: ")
password = input("Enter password: ")

# Using parameterized queries to prevent SQL injection
query = "SELECT * FROM users WHERE username = ? AND password = ?"
cursor.execute(query, (username, password))

# Fetch and process results
results = cursor.fetchall()
for row in results:
    print(row)

# Close the connection
conn.close()

Best Practices

1. Sanitize User Input: Remove or escape characters that could be used for SQL injection.
2. Use ORM: An ORM framework can help manage database queries more securely.
3. Least Privilege: Ensure database users have the least privileges necessary.
4. Regular Security Audits: Regularly review and audit your code for potential SQL injection vulnerabilities.
5. Security Libraries: Utilize security libraries and frameworks that help manage and prevent SQL injection.