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Resolve vulnerability: Improper neutralization of special elements used in an SQL Command ('SQL Injection')

Justin Mandellrequested to merge
remediate/improper-neutralization-of-special-elements-used-in-an-sql-comm-D20250725T195151 into nmccorrison-main-patch-4db8

Vulnerability finding detected in merge request: add 209 (!62) • Justin Mandell

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Description:

Detected user input used to manually construct a SQL string. This is usually bad practice because manual construction could accidentally result in a SQL injection. An attacker could use a SQL injection to steal or modify contents of the database. Instead, use a parameterized query which is available by default in most database engines. Alternatively, consider using an object-relational mapper (ORM) such as SQLAlchemy which will protect your queries.

SQL Injections are a critical type of vulnerability that can lead to data or system compromise. By dynamically generating SQL query strings, user input may be able to influence the logic of an SQL statement. This could lead to an malicious parties accessing information they should not have access to, or in some circumstances, being able to execute OS functionality or code.

Replace all dynamically generated SQL queries with parameterized queries. In situations where dynamic queries must be created, never use direct user input, but instead use a map or dictionary of valid values and resolve them using a user supplied key.

For example, some database drivers do not allow parameterized queries for > or < comparison operators. In these cases, do not use a user supplied > or < value, but rather have the user supply a gt or lt value. The alphabetical values are then used to look up the > and < values to be used in the construction of the dynamic query. The same goes for other queries where column or table names are required but cannot be parameterized. Data that is possible user-controlled from a python request is passed to execute() function. To remediate this issue, use SQLAlchemy statements which are built with query parameterization and therefore not vulnerable to sql injection.

If for some reason this is not feasible, ensure calls including user-supplied data pass it in to the params parameter of the execute() method. Below is an example using execute(), passing in user-supplied data as params. This will treat the query as a parameterized query and params as strictly data, preventing any possibility of SQL Injection.

name = request.args.get('name')
req = text('SELECT * FROM student WHERE firstname = :x')
result = db.session.execute(req, {"x":name})

For more information on QuerySets see:

Summary:

SQL Injection Vulnerability Analysis

The reported vulnerability is "Improper neutralization of special elements used in an SQL Command ('SQL Injection')" (CWE-89). This is a critical security issue where user input is directly incorporated into SQL queries without proper sanitization, allowing attackers to manipulate the query structure.

Issues Found

I identified two instances of SQL injection vulnerabilities in the code:

  1. In the /login endpoint, user-supplied username and password values were directly interpolated into the SQL query using f-strings:

    query = f"SELECT * FROM users WHERE username = '{username}' AND password = '{password}'"

  2. In the /user/<int:user_id> endpoint, the user_id parameter was directly interpolated into the query:

    query = f"SELECT * FROM users WHERE id = {user_id}"

Implemented Fixes

I replaced the vulnerable string interpolation with parameterized queries using the MySQL connector's parameter substitution mechanism:

  1. For the login endpoint:

    query = "SELECT * FROM users WHERE username = %s AND password = %s"
cursor.execute(query, (username, password))

  2. For the user endpoint:

    query = "SELECT * FROM users WHERE id = %s"
cursor.execute(query, (user_id,))

Security Improvement

The fixes prevent SQL injection by:

  1. Separating the SQL command structure from the data
  2. Ensuring user input is treated strictly as data, not executable code
  3. Letting the database driver handle proper escaping and quoting of parameters

This approach follows the principle of parameterized queries recommended in the vulnerability report, which is the standard best practice for preventing SQL injection attacks.

Note: While the code now prevents SQL injection, storing passwords in plaintext is another security concern that should be addressed in a production system by implementing proper password hashing.

Identifiers:

  • A1:2017 - Injection
  • A03:2021 - Injection
  • CWE-89
  • python_flask_rule-flask-tainted-sql-string

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