threat-modeling.md

Threat Model Analysis for tokio-rs/tokio

Threat: Unbounded Task Spawning via Malicious Input

• Threat: Unbounded Task Spawning via Malicious Input

  • Description: An attacker sends crafted input that causes the application to spawn a very large number of Tokio tasks via tokio::task::spawn or tokio::task::spawn_blocking. The attacker might repeatedly send such requests. The vulnerability lies in how the application uses Tokio's task spawning functions based on untrusted input.
  • Impact: Resource exhaustion (CPU, memory, file descriptors), leading to denial of service. The application becomes unresponsive or crashes.
  • Affected Tokio Component: tokio::task::spawn, tokio::task::spawn_blocking, and any application code that uses these functions based on external, attacker-controlled input.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Task Limiter: Use a Semaphore (from tokio::sync) or a custom task limiter to restrict the maximum number of concurrent tasks created via Tokio. Reject or queue new requests when the limit is reached. This is a Tokio-specific mitigation.
    • Bounded Channels: Use bounded mpsc channels (tokio::sync::mpsc::channel with a defined capacity) for communication between tasks spawned by Tokio. This prevents unbounded queue growth if a consumer task is slower than a producer, a scenario often exploited in DoS attacks.
    • Input Validation (Application-Level, but Essential): Strictly validate and sanitize all input that influences task creation. This is crucial, but it's application logic, not a Tokio-specific feature.
    • Rate Limiting (Often External, but Important): Implement rate limiting (within the application or using a reverse proxy) to limit the frequency of requests. This is often handled outside of Tokio.
    • Monitoring (Tokio-Specific Aspects): Monitor the number of active tasks managed by Tokio and resource usage. Set alerts for unusual spikes. Use Tokio's tracing facilities to monitor task creation.

Threat: Blocking I/O within Async Context

• Threat: Blocking I/O within Async Context

  • Description: A blocking operation (e.g., std::fs::read_to_string, a synchronous HTTP request, a long CPU-bound calculation without spawn_blocking) is performed within an async function or a Tokio task. This blocks the Tokio worker thread. The vulnerability is the misuse of Tokio by introducing blocking calls into its asynchronous context.
  • Impact: The Tokio worker thread becomes blocked, preventing other tasks managed by Tokio from making progress. This leads to a denial of service, even with few requests. Latency increases significantly.
  • Affected Tokio Component: The entire Tokio runtime is affected, as a single blocked worker thread can stall the entire system. Specifically, any async fn or code within a tokio::task::spawn or tokio::task::spawn_blocking block that contains blocking calls.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Asynchronous Libraries: Use Tokio's asynchronous equivalents for all I/O operations (e.g., tokio::fs, tokio::net, asynchronous HTTP clients). This is the core mitigation – using Tokio correctly.
    • spawn_blocking for CPU-Bound Work: Offload long-running CPU-bound computations to a separate thread pool using tokio::task::spawn_blocking. This is a Tokio-specific mitigation.
    • Code Review (Essential, but General): Thoroughly review all code within async functions and Tokio tasks for any blocking operations.
    • Third-Party Library Audit (Important, but General): Carefully audit all third-party libraries.
    • Profiling (Tokio-Specific Aspects): Use profiling tools, potentially integrated with Tokio's tracing, to identify blocking operations during development. Look for long periods where Tokio worker threads are not making progress.

Threat: Slowloris-Style Attack on Tokio Listener

• Threat: Slowloris-Style Attack on Tokio Listener

  • Description: An attacker establishes many TCP connections to the application's Tokio listener (tokio::net::TcpListener) but sends data very slowly or keeps connections open without sending data. This exploits how Tokio handles network connections.
  • Impact: Exhaustion of connection resources (file descriptors, memory) managed by Tokio. The application becomes unable to accept new connections, leading to denial of service.
  • Affected Tokio Component: tokio::net::TcpListener, tokio::net::TcpStream, and any code that uses these components to handle incoming connections.
  • Risk Severity: High
  • Mitigation Strategies:
    • Timeouts: Implement strict timeouts on all I/O operations using tokio::time::timeout. This is a Tokio-specific mitigation. Set reasonable timeouts for accept, read, and write operations.
    • Connection Limits (Tokio and OS): Configure connection limits on the Tokio runtime and the underlying operating system. This involves both Tokio-specific configuration and OS-level settings.
    • Reverse Proxy (Often External): Use a reverse proxy (like Nginx or HAProxy). This is often handled outside of Tokio.
    • Connection Tracking (Tokio-Specific Aspects): Monitor the number of open connections and their state using Tokio's tracing or metrics facilities. Identify and close connections that are idle for an extended period.

Threat: Data Race on Shared Mutable State (Specifically within Tokio Tasks)

• Threat: Data Race on Shared Mutable State (Specifically within Tokio Tasks)

  • Description: Multiple Tokio tasks access and modify the same shared mutable data without proper synchronization using Tokio's synchronization primitives. The attacker might send concurrent requests to trigger the race. The core issue is incorrect use of Tokio's concurrency model.
  • Impact: Data corruption, inconsistent application state, unpredictable behavior, potential information disclosure, or crashes.
  • Affected Tokio Component: Any code that shares mutable data between Tokio tasks without using Tokio's synchronization primitives correctly. Specifically, incorrect use of tokio::sync::Mutex, tokio::sync::RwLock, or atomics within the context of Tokio tasks.
  • Risk Severity: High
  • Mitigation Strategies:
    • Tokio Synchronization Primitives: Use Tokio's synchronization primitives correctly:
      • tokio::sync::Mutex: For exclusive access.
      • tokio::sync::RwLock: For read-write access.
      • Atomic types (e.g., std::sync::atomic): For simple operations (can be used with Tokio).
      • Channels (tokio::sync::mpsc, tokio::sync::oneshot): For message passing, avoiding shared mutable state. This is a key Tokio-specific approach.
    • Minimize Shared Mutable State (General Principle): Favor message passing and immutable data structures.
    • loom (Tokio-Specific Testing): Use the loom crate for testing concurrent code that uses Tokio. loom helps detect data races.

Threat: Improper Use of spawn_blocking with Privileged Code

• Threat: Improper Use of spawn_blocking with Privileged Code

  • Description: An attacker provides input that influences code executed within tokio::task::spawn_blocking, and that code interacts with privileged resources without proper validation. This is a specific misuse of a Tokio feature.
  • Impact: The attacker might gain unauthorized access to system resources, execute arbitrary code with elevated privileges, or bypass security restrictions.
  • Affected Tokio Component: tokio::task::spawn_blocking, and any code executed within it that interacts with privileged resources.
  • Risk Severity: High
  • Mitigation Strategies:
    • Input Validation (Essential, but General): Strictly validate and sanitize all input.
    • Principle of Least Privilege (General Principle): Grant only necessary permissions.
    • Sandboxing (Often External): Consider using sandboxing techniques.
    • Code Review (Essential, but General): Carefully review any code executed within spawn_blocking.