Describe SQL injection attack

  • 5 minutes

SQL injection is one of the most dangerous and prevalent web application security vulnerabilities. This attack technique makes it possible to execute malicious SQL statements that control a database server behind a web application. Understanding how SQL injection works is essential for building secure applications.

What is SQL injection

Definition: SQL injection occurs when an attacker inserts malicious SQL code into application queries. Instead of treating user input as data, the application mistakenly executes it as code, allowing attackers to manipulate database operations.

How it works: Web applications often construct SQL queries by combining static SQL with user-provided input. When applications don't properly validate or sanitize this input, attackers can inject additional SQL commands that the database executes alongside the intended query.

Simple example: Consider a login form that checks credentials with this query:

SELECT * FROM users WHERE username = 'inputUsername' AND password = 'inputPassword'

An attacker might enter admin' -- as the username. This transforms the query into:

SELECT * FROM users WHERE username = 'admin' --' AND password = 'inputPassword'

The -- characters start a SQL comment, effectively removing the password check. The attacker gains access without knowing the password.

What attackers can accomplish

SQL injection vulnerabilities enable attackers to bypass application security measures and perform unauthorized actions:

Bypass authentication and authorization: Attackers can circumvent login mechanisms to access accounts without valid credentials. They can elevate privileges to gain administrative access even with low-privilege accounts.

Retrieve entire database contents: Once they've injected malicious SQL, attackers can extract all data from the database including customer information, personal data, trade secrets, intellectual property, and confidential business information. They're not limited to data the application normally displays.

Modify or delete database records: Attackers can use SQL injection to insert, update, or delete records. They might add new administrative accounts, modify prices in e-commerce systems, or delete audit logs to cover their tracks.

Execute operating system commands: In some configurations, attackers can execute commands on the underlying operating system through database features. This can lead to complete server compromise.

Perform denial of service: Attackers can craft queries that consume excessive resources, effectively making the application unavailable to legitimate users.

Widespread impact

Affects any SQL-based application: SQL injection vulnerabilities can affect any website or web application that uses SQL databases including:

  • MySQL applications.
  • Oracle database systems.
  • Microsoft SQL Server applications.
  • PostgreSQL databases.
  • SQLite implementations.
  • Any other SQL-based database systems.

The vulnerability exists in the application code, not the database software itself. Even when using secure, up-to-date database systems, poor application code creates vulnerabilities.

Sensitive data at risk: Criminals exploit SQL injection to gain unauthorized access to sensitive information:

  • Customer information: Names, addresses, payment details, purchase history.
  • Personal data: Social security numbers, dates of birth, medical records, financial information.
  • Business data: Trade secrets, proprietary algorithms, strategic plans, partner agreements.
  • Intellectual property: Research data, unpublished content, source code.
  • Authentication credentials: Passwords, API keys, tokens, certificates.

Prevalence and significance

Among the most dangerous vulnerabilities: SQL injection attacks are among the oldest, most prevalent, and most dangerous web application vulnerabilities. Despite decades of awareness and available defenses, SQL injection remains a common attack vector.

OWASP recognition: The OWASP organization (Open Web Application Security Project) lists injection attacks prominently in their OWASP Top 10 document, which identifies the most critical security risks to web applications. The continued presence in this list demonstrates the ongoing relevance of SQL injection as a threat.

Why it persists:

  • Legacy applications: Many older applications were built before SQL injection was well understood and haven't been updated with proper defenses.
  • Developer awareness gaps: Not all developers receive adequate security training, leading to vulnerable code even in new applications.
  • Complexity of modern applications: Large codebases with many database queries provide numerous potential injection points.
  • Time pressures: Development deadlines sometimes lead to shortcuts in security practices.

Prevention is essential

Understanding SQL injection attacks is the first step toward prevention. Organizations must:

  • Train developers on secure coding practices.
  • Use parameterized queries and prepared statements.
  • Validate and sanitize all user input.
  • Apply the principle of least privilege to database accounts.
  • Conduct regular security testing including automated vulnerability scanning.
  • Perform code reviews with security focus.
  • Monitor applications for suspicious database activity.

Additional resources

The Azure security center team provides workflow automation playbooks you can explore to learn how vulnerabilities are exploited to trigger various attack types including virus attacks, DDoS attacks, and data exfiltration scenarios. These playbooks demonstrate real-world attack patterns and help security teams prepare appropriate defenses.