SQL Injection Fix: CWE 89 In Python Api.py

Nov 20, 2025 by Alex Johnson 43 views

SQL Injection Vulnerability in `api.py`: How to Fix CWE 89?

Introduction to SQL Injection

SQL Injection (SQLi) is a critical web security vulnerability that allows attackers to interfere with the queries that an application makes to its database. Attackers can view, bypass security measures, modify, or delete data in the database. In some cases, an attacker may even be able to take over the database server. This article delves into a specific instance of an SQL Injection vulnerability identified in api.py, providing a detailed explanation and practical steps to remediate it.

The vulnerability falls under CWE-89, which stands for Improper Neutralization of Special Elements used in an SQL Command. This occurs when user-supplied input is incorporated into an SQL query without proper sanitization or parameterization. The specific location of the vulnerability is in the file source-code/api.py on line 48, within the context of the andrewgc-dem1 Petstore API project, which utilizes Flask.

Understanding the Vulnerability

To fully grasp the issue, it's essential to understand how SQL Injection works. Imagine a scenario where a web application takes user input, such as a username, and uses it directly in an SQL query. If an attacker inputs a carefully crafted string instead of a username, they could inject malicious SQL code into the query. This malicious code can then be executed by the database, leading to unauthorized access or data manipulation. The consequences of SQL Injection can be severe, including data breaches, data corruption, and even complete system compromise. Therefore, understanding and preventing this type of vulnerability is paramount for maintaining the security and integrity of web applications.

In the context of the provided information, the vulnerability lies within a database query constructed using flaskext.mysql.MySQL.cursors.Cursor.execute(). This method is used to execute SQL queries, and when it dynamically constructs a query using user-supplied input, it opens the door for SQL Injection. The attacker can manipulate the input in such a way that it alters the structure and meaning of the query, leading to unintended actions on the database. It is imperative to identify and address these vulnerabilities promptly to safeguard sensitive data and ensure the overall security of the application.

Locating the Vulnerable Code

The identified vulnerable code is located in source-code/api.py at line 48. The specific snippet involves the use of flaskext.mysql.MySQL.cursors.Cursor.execute(), which constructs a dynamic SQL query. Dynamic SQL queries, while sometimes necessary, are prone to SQL Injection attacks if not handled carefully. When user-supplied input is directly embedded into the query string, it creates an opportunity for attackers to inject malicious SQL code. In this case, the lack of proper input sanitization or parameterization allows the attacker to manipulate the query and potentially gain unauthorized access to the database or perform other malicious actions.

To effectively address this vulnerability, it is essential to understand the flow of data and how user input is being incorporated into the SQL query. By examining the surrounding code, developers can identify the source of the user input and the exact point where it is being used in the query construction. This understanding is crucial for implementing the appropriate remediation strategies, such as using parameterized queries or input validation, to prevent SQL Injection attacks.

Impact of SQL Injection

The impact of an SQL Injection vulnerability can be devastating. An attacker exploiting this flaw could:

Data Breach: Access sensitive data, such as user credentials, personal information, and financial details.
Data Manipulation: Modify or delete data, leading to data corruption and loss of integrity.
Unauthorized Access: Bypass authentication and authorization mechanisms to gain access to restricted areas of the application.
Denial of Service: Disrupt the application's availability by injecting queries that cause performance degradation or crashes.
Complete System Compromise: In severe cases, gain control of the database server, potentially leading to full system compromise.

The specific context of the Petstore API application suggests that sensitive data related to pets, users, or transactions could be at risk. An attacker could potentially steal user credentials, modify pet information, or even gain unauthorized access to administrative functions. Therefore, addressing this SQL Injection vulnerability is crucial for protecting the application and its users from potential harm.

Remediation Techniques

1. Use Parameterized Queries (Prepared Statements)

The most effective way to prevent SQL Injection is to use parameterized queries, also known as prepared statements. Parameterized queries treat user input as data rather than executable code. This means that even if an attacker injects SQL code into the input, the database will not interpret it as part of the query structure.

In Python, when using flaskext.mysql, parameterized queries can be implemented by passing the query and parameters as separate arguments to the execute() method. Here’s how to implement parameterized queries:

# Vulnerable code
#cursor.execute("SELECT * FROM pets WHERE name = '" + request.args.get('name') + "'")

# Secure code using parameterized query
name = request.args.get('name')
query = "SELECT * FROM pets WHERE name = %s"
cursor.execute(query, (name,))

In this example, %s acts as a placeholder for the user-provided name. The database driver then safely substitutes the value, ensuring that it is treated as data and not as part of the SQL command.

2. Input Validation and Sanitization

Validating and sanitizing user input is another crucial step in preventing SQL Injection attacks. Input validation involves verifying that the input conforms to the expected format and type, while sanitization involves removing or encoding any characters that could be interpreted as SQL code. This is a secondary defense mechanism and should be used in conjunction with parameterized queries, not as a replacement.

For example, if the application expects an integer, it should verify that the input is indeed an integer before using it in a query. If it expects a string, it should escape any special characters that could be used in an SQL Injection attack. Here’s an example of input sanitization:

import re

def sanitize_string(input_string):
    # Remove any non-alphanumeric characters except spaces
    sanitized_string = re.sub(r'[^a-zA-Z0-9\s]', '', input_string)
    return sanitized_string

name = request.args.get('name')
sanitized_name = sanitize_string(name)
query = "SELECT * FROM pets WHERE name = %s"
cursor.execute(query, (sanitized_name,))

In this example, the sanitize_string function uses a regular expression to remove any characters that are not alphanumeric or spaces, providing an additional layer of security.

3. Principle of Least Privilege

The principle of least privilege dictates that the database user the application uses should only have the minimum necessary permissions to perform its functions. This means that the user should not have permissions to create, alter, or delete tables, or to access system tables. If an SQL Injection attack occurs, limiting the database user's privileges can significantly reduce the potential damage.

For example, if the application only needs to read data from certain tables, the database user should only have SELECT privileges on those tables. This can prevent an attacker from using SQL Injection to modify or delete data, even if they manage to inject malicious SQL code.

4. Web Application Firewalls (WAFs)

Web Application Firewalls (WAFs) can help detect and block SQL Injection attacks by analyzing HTTP traffic and identifying malicious patterns. A WAF can be deployed in front of the application to filter out suspicious requests before they reach the application server. This is not a foolproof solution, but it provides an additional layer of defense.

WAFs use a variety of techniques to identify SQL Injection attacks, including signature-based detection, anomaly detection, and behavioral analysis. They can also be configured to block requests that contain specific SQL keywords or patterns.

Implementing a Secure Solution

To effectively address the SQL Injection vulnerability in api.py, follow these steps:

Identify the vulnerable code: Pinpoint the exact location where user input is being used in SQL queries without proper sanitization or parameterization. In this case, it's line 48 in source-code/api.py.
Implement Parameterized Queries: Modify the code to use parameterized queries instead of dynamically constructing SQL queries. This ensures that user input is treated as data and not executable code.
Validate User Input: Add input validation to ensure that user-supplied data conforms to the expected format and type. This can help prevent malicious input from reaching the database.
Apply Input Sanitization: Sanitize user input by removing or encoding any characters that could be interpreted as SQL code. This provides an additional layer of security.
Test Thoroughly: After implementing the fixes, thoroughly test the application to ensure that the vulnerability has been successfully addressed and that no new issues have been introduced.

Here’s an example of how to implement a secure solution using parameterized queries and input validation:

from flask import Flask, request
import MySQLdb
import re

app = Flask(__name__)

# Database configuration (replace with your actual credentials)
app.config['MYSQL_HOST'] = 'localhost'
app.config['MYSQL_USER'] = 'your_user'
app.config['MYSQL_PASSWORD'] = 'your_password'
app.config['MYSQL_DB'] = 'petstore'


def get_db_connection():
    return MySQLdb.connect(host=app.config['MYSQL_HOST'],
                           user=app.config['MYSQL_USER'],
                           passwd=app.config['MYSQL_PASSWORD'],
                           db=app.config['MYSQL_DB'])


def sanitize_string(input_string):
    # Remove any non-alphanumeric characters except spaces
    sanitized_string = re.sub(r'[^a-zA-Z0-9\s]', '', input_string)
    return sanitized_string


@app.route('/pets')
def get_pets():
    name = request.args.get('name')

    if not name:
        return "Please provide a pet name", 400

    sanitized_name = sanitize_string(name)

    try:
        conn = get_db_connection()
        cursor = conn.cursor()
        query = "SELECT * FROM pets WHERE name = %s"
        cursor.execute(query, (sanitized_name,))
        pets = cursor.fetchall()
        cursor.close()
        conn.close()

        if pets:
            return str(pets)
        else:
            return "No pets found with that name", 404

    except MySQLdb.Error as e:
        return f"Database error: {e}", 500


if __name__ == '__main__':
    app.run(debug=True)

In this example, the code uses parameterized queries to prevent SQL Injection. It also sanitizes user input to remove any potentially malicious characters. Additionally, it includes error handling to catch any database-related issues.

Conclusion

SQL Injection vulnerabilities pose a significant threat to web applications. By understanding the principles behind SQL Injection and implementing appropriate remediation techniques, developers can protect their applications and data from attack. Using parameterized queries, validating and sanitizing input, applying the principle of least privilege, and employing Web Application Firewalls are all effective strategies for preventing SQL Injection attacks. Regular security assessments and code reviews are also essential for identifying and addressing potential vulnerabilities before they can be exploited.

By diligently following these practices, you can significantly reduce the risk of SQL Injection and ensure the security and integrity of your web applications. For further information and resources on preventing SQL Injection, visit the OWASP SQL Injection Prevention Cheat Sheet.