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attack-surface.md

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Attack Surface Analysis for yiisoft/yii2

Attack Surface: Insufficient Input Validation

  • Description: Failure to properly validate user-supplied input before processing it.
  • Yii2 Contribution: Yii2 relies on developers to define validation rules within model classes. Incomplete or incorrectly implemented validation rules directly lead to this attack surface.
  • Example: A Yii2 application's user registration form model lacks validation for the email field. An attacker can submit a registration request with an email address that is excessively long, causing a buffer overflow in the database or application logic during processing.
  • Impact: SQL Injection, Cross-Site Scripting (XSS), data corruption, application logic bypass, potential for Remote Code Execution (RCE) in complex scenarios.
  • Risk Severity: High
  • Mitigation Strategies:
    • Define comprehensive validation rules in Yii2 models: Utilize Yii2's validation framework extensively for all user inputs.
    • Use appropriate validation rule types: Select validation rules that accurately match the expected data format and constraints (e.g., email, integer, string, regularExpression, unique).
    • Implement server-side validation as primary defense: Always enforce validation on the server-side, regardless of client-side validation, as client-side checks can be easily bypassed.
    • Regularly review and update validation rules: Adapt validation rules as application requirements change and new input fields are introduced.

Attack Surface: SQL Injection via Query Builder or Raw SQL

  • Description: Exploiting vulnerabilities in SQL queries to inject malicious SQL code, leading to unauthorized database access or manipulation.
  • Yii2 Contribution: While Yii2's Active Record and Query Builder are designed to mitigate SQL injection, developers can still introduce vulnerabilities by using raw SQL queries or misusing Query Builder methods in insecure ways within Yii2 applications.
  • Example: A Yii2 controller action constructs a database query using string concatenation with user input: $username = Yii::$app->request->get('username'); Yii::$app->db->createCommand("SELECT * FROM users WHERE username = '" . $username . "'")->queryOne();. An attacker can inject SQL code by providing a malicious username like ' OR '1'='1.
  • Impact: Data breach, data manipulation, data deletion, denial of service, potential for Remote Code Execution (RCE) in certain database configurations.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Always use parameterized queries or bound parameters: Utilize Yii2's Query Builder and Active Record features with parameter binding to ensure safe SQL query construction.
    • Avoid raw SQL queries whenever possible: Rely on Query Builder and Active Record for database interactions to leverage built-in protection mechanisms.
    • Carefully sanitize input used in LIKE clauses: When using user input in LIKE conditions, employ proper escaping or parameterization techniques to prevent injection.
    • Conduct regular code reviews focusing on database interactions: Specifically audit code sections that construct database queries, especially when user input is involved.

Attack Surface: Cross-Site Scripting (XSS) due to Inadequate Output Sanitization

  • Description: Injecting malicious scripts into web pages viewed by other users, typically by exploiting vulnerabilities in output encoding.
  • Yii2 Contribution: If developers fail to properly sanitize user-provided data before displaying it within Yii2 views, XSS vulnerabilities can arise. Yii2 provides helper functions for output encoding, but their correct and consistent usage is the developer's responsibility.
  • Example: A Yii2 view directly outputs user-submitted content without encoding: <?= $model->userInput ?>. If a user submits <img src="x" onerror="alert('XSS')"> as userInput, this script will execute in the browsers of other users viewing this page.
  • Impact: Session hijacking, account takeover, website defacement, redirection to malicious websites, theft of sensitive user information.
  • Risk Severity: High
  • Mitigation Strategies:
    • Use output encoding functions consistently in Yii2 views: Employ Yii2's HTML encoding helpers like Html::encode() or HtmlPurifier whenever displaying user-generated content.
    • Apply context-aware output encoding: Choose the appropriate encoding method based on the output context (HTML, JavaScript, URL, CSS).
    • Implement Content Security Policy (CSP) headers: Utilize CSP to restrict the sources from which the browser can load resources, reducing the impact of XSS attacks.
    • Regularly audit Yii2 views for output encoding: Ensure all instances of user-generated content output are properly encoded to prevent XSS vulnerabilities.

Attack Surface: Unrestricted File Uploads

  • Description: Allowing users to upload files without proper validation and restrictions on file type, size, and content.
  • Yii2 Contribution: Yii2 provides file upload handling capabilities, but the framework itself does not enforce security restrictions. Developers must implement validation and security measures within their Yii2 application to prevent malicious file uploads.
  • Example: A Yii2 application allows users to upload files without validating file extensions. An attacker uploads a PHP script disguised as an image (e.g., evil.php.jpg). If the web server executes PHP files in the upload directory, accessing the uploaded file directly can lead to Remote Code Execution.
  • Impact: Remote Code Execution (RCE), Cross-Site Scripting (XSS), website defacement, denial of service (via large file uploads), information disclosure.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Validate file types rigorously: Restrict allowed file extensions and MIME types to only necessary and safe formats. Use server-side validation for file type checks.
    • Validate file size: Limit the maximum allowed file size to prevent denial of service and resource exhaustion.
    • Sanitize and rename uploaded files: Rename uploaded files to prevent directory traversal and other file system-related vulnerabilities.
    • Store uploaded files outside the webroot: Store uploaded files in a directory that is not directly accessible by the web server to prevent direct execution of uploaded scripts.
    • Implement antivirus scanning on uploads: Scan uploaded files for malware before storing them to prevent the introduction of malicious content.
    • Consider using dedicated file storage services: Utilize cloud-based file storage services that often provide built-in security features and reduce the attack surface on the application server.