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attack-surface.md

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Attack Surface Analysis for tornadoweb/tornado

Attack Surface: Asynchronous Request Flooding (DoS)

  • Description: Attackers overwhelm the server by sending a large volume of asynchronous requests that consume resources without quickly completing, leading to service disruption.
  • Tornado Contribution: Tornado's non-blocking I/O and asynchronous nature, while efficient, can make it easier for attackers to initiate and maintain a high volume of concurrent requests, potentially exhausting server resources.
  • Example: An attacker scripts a botnet to send thousands of requests to a Tornado application endpoint that triggers a resource-intensive operation. The server becomes overloaded and unable to handle legitimate user requests.
  • Impact: Application unavailability, performance degradation, financial losses due to downtime.
  • Risk Severity: High
  • Mitigation Strategies:
    • Implement request rate limiting at the application level or using a reverse proxy.
    • Set limits on resources consumed by each request (e.g., database connections, API timeouts).
    • Implement request prioritization and load balancing.
    • Deploy a Web Application Firewall (WAF).

Attack Surface: Race Conditions in Asynchronous Handlers

  • Description: Concurrent asynchronous requests interact with shared application state in an unsynchronized manner, leading to unexpected behavior and potential vulnerabilities.
  • Tornado Contribution: Tornado's asynchronous programming model encourages concurrency, increasing the likelihood of race conditions if developers are not careful about managing shared state and synchronization.
  • Example: Two concurrent requests attempt to update a user's account balance. Due to a race condition, the final balance might be incorrect, leading to financial discrepancies or unauthorized access.
  • Impact: Data corruption, inconsistent application state, security bypasses (e.g., unauthorized access).
  • Risk Severity: High to Critical
  • Mitigation Strategies:
    • Minimize shared mutable state within asynchronous handlers.
    • Use synchronization primitives like locks (asyncio.Lock, threading.Lock) or atomic operations.
    • Employ database transactions for atomic operations.
    • Conduct thorough code reviews and concurrency testing.

Attack Surface: Server-Side Template Injection (SSTI)

  • Description: Attackers inject malicious code into template variables that are not properly sanitized, leading to arbitrary code execution on the server when the template is rendered.
  • Tornado Contribution: If using Tornado's built-in template engine (tornado.template) and directly embedding user-provided data into templates without proper escaping, it becomes vulnerable to SSTI.
  • Example: An attacker injects malicious code like {{ system('rm -rf /') }} into a user-controlled template variable. If rendered without escaping, the code executes on the server.
  • Impact: Remote code execution, full server compromise, data breaches, denial of service.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Always escape user-provided data before embedding it into templates using Tornado's escaping mechanisms.
    • Consider template sandboxing (with caution).
    • Validate and sanitize user input before template rendering.
    • Run the Tornado application with minimal privileges.
    • Implement Content Security Policy (CSP).

Attack Surface: Path Traversal in Static File Serving

  • Description: Attackers manipulate URLs to access files outside the intended static file directory when using tornado.web.StaticFileHandler.
  • Tornado Contribution: Improper configuration of tornado.web.StaticFileHandler without sufficient restrictions on the path argument can allow directory traversal.
  • Example: A StaticFileHandler is configured for /static/. An attacker crafts a URL like /static/../../../../etc/passwd to access sensitive system files.
  • Impact: Unauthorized access to sensitive files, source code disclosure, configuration file access.
  • Risk Severity: High
  • Mitigation Strategies:
    • Restrict the path argument of StaticFileHandler to the intended static file directory.
    • Sanitize and validate user-provided paths or filenames.
    • Apply principle of least privilege to file system permissions for the Tornado process.
    • Conduct regular security audits of StaticFileHandler configuration.

Attack Surface: Regular Expression Denial of Service (ReDoS) in Route Matching

  • Description: Complex and vulnerable regular expressions in route definitions can be exploited to cause excessive CPU consumption during route matching, leading to DoS.
  • Tornado Contribution: Tornado's routing uses regular expressions for URL matching. Vulnerable regex patterns can be exploited for ReDoS.
  • Example: A route uses a vulnerable regex like r"^(a+)+$". An attacker sends a URL like /aaaaaaaaaaaaaaaaaaaaaaaaaaaaa! causing excessive CPU usage during route matching.
  • Impact: Application unavailability, performance degradation, resource exhaustion.
  • Risk Severity: High
  • Mitigation Strategies:
    • Design route regular expressions to be efficient and avoid ReDoS-vulnerable patterns.
    • Test regular expressions for ReDoS vulnerabilities.
    • Limit regex complexity and consider simpler routing methods.
    • Implement request timeouts.

Attack Surface: WebSocket Injection (XSS via WebSockets)

  • Description: Malicious payloads injected into WebSocket messages are not properly sanitized and are reflected back to other clients, leading to cross-site scripting (XSS).
  • Tornado Contribution: Unsanitized WebSocket handlers in Tornado applications can become a vector for XSS if messages are not validated and escaped.
  • Example: In a chat application, an attacker sends a WebSocket message with <script>alert('XSS')</script>. If broadcasted unsanitized, other clients' browsers will execute the script.
  • Impact: Cross-site scripting (XSS), session hijacking, malicious actions performed on behalf of users.
  • Risk Severity: High
  • Mitigation Strategies:
    • Thoroughly validate and sanitize all data received from WebSocket clients.
    • Encode or escape data before sending it back to WebSocket clients, using context-aware escaping.
    • Implement Content Security Policy (CSP).
    • Regularly audit WebSocket handlers for injection vulnerabilities.

Attack Surface: Exposure of Debug Mode in Production

  • Description: Leaving Tornado's debug mode enabled in production environments exposes sensitive information and potentially allows remote code execution.
  • Tornado Contribution: Tornado has a debug mode that is intended for development but must be disabled in production.
  • Example: Debug mode is left enabled in production. Attackers access debug endpoints, view stack traces, application state, or potentially use debugging tools to execute code.
  • Impact: Information disclosure, remote code execution, full server compromise.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Disable debug mode in production deployments. Ensure debug=False is set in tornado.web.Application settings for production.
    • Implement proper configuration management to ensure debug mode is consistently disabled in production environments.
    • Regularly review application configuration to verify debug mode is disabled.