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attack-surface.md

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Attack Surface Analysis for tokio-rs/tokio

Attack Surface: Asynchronous Race Conditions

  • Description: Concurrent execution of asynchronous tasks accessing shared mutable state without proper synchronization leads to unpredictable behavior and potential vulnerabilities.
    • How Tokio Contributes: Tokio's core asynchronous model enables concurrent task execution, making race conditions possible if developers don't implement proper synchronization. This is a direct consequence of using Tokio's asynchronous capabilities.
    • Example: Two Tokio tasks concurrently modify a shared data structure (e.g., a HashMap) without using a tokio::sync::Mutex. An attacker could time requests to exploit this and corrupt the data.
    • Impact: Data corruption, inconsistent application state, denial of service, potential for privilege escalation (depending on the affected data).
    • Risk Severity: High (can lead to significant data integrity issues and potentially exploitable vulnerabilities).
    • Mitigation Strategies:
      • Use Tokio Synchronization Primitives: Employ tokio::sync::Mutex, RwLock, Semaphore correctly to protect shared mutable state.
      • Minimize Shared Mutability: Favor immutable data and message passing (e.g., using Tokio channels) over shared mutable state.
      • Atomic Operations: Use std::sync::atomic for simple shared variables where appropriate, ensuring they are used correctly within the Tokio context.
      • Code Reviews: Focus on asynchronous code and shared state access within Tokio tasks.
      • Testing: Use loom and other concurrency testing tools to specifically target race conditions in Tokio-based code.

Attack Surface: Asynchronous Deadlocks

  • Description: Two or more Tokio tasks become blocked indefinitely, waiting for each other to release resources (often locks), leading to application unresponsiveness.
    • How Tokio Contributes: Tokio's task scheduling and synchronization mechanisms (specifically, tokio::sync primitives) are directly involved in creating the conditions for deadlocks if misused.
    • Example: Task A (within Tokio) holds tokio::sync::Mutex X and awaits acquisition of tokio::sync::Mutex Y, while Task B (also within Tokio) holds Y and awaits X.
    • Impact: Denial of service (application becomes completely unresponsive).
    • Risk Severity: High (complete application failure).
    • Mitigation Strategies:
      • Careful Lock Ordering: Establish and enforce a consistent order for acquiring tokio::sync locks across all Tokio tasks.
      • Lock Timeouts: Use tokio::sync::Mutex::try_lock_for to prevent indefinite blocking.
      • Avoid Holding Locks Across Await: Minimize holding tokio::sync locks across .await points within Tokio tasks.
      • Deadlock Detection (tokio-console): Utilize tokio-console to identify and diagnose deadlocks specifically within the Tokio runtime.
      • Code Reviews: Focus on tokio::sync lock acquisition and release patterns.

Attack Surface: Task Starvation

  • Description: An attacker floods the Tokio runtime with numerous long-running or computationally intensive tasks, preventing legitimate tasks from receiving adequate processing time.
    • How Tokio Contributes: Tokio's task scheduler is directly targeted by this attack. The attacker exploits Tokio's ability to handle many tasks, but overwhelms it.
    • Example: An attacker submits thousands of Tokio tasks that perform computationally expensive operations, saturating the Tokio worker threads.
    • Impact: Denial of service (legitimate requests are delayed or dropped due to Tokio task queue saturation).
    • Risk Severity: High (significant performance degradation and potential unavailability).
    • Mitigation Strategies:
      • Rate Limiting (Tokio-Aware): Implement rate limiting, considering the asynchronous nature of Tokio tasks. Use libraries that integrate well with Tokio.
      • Bounded Task Queues (Tokio): Use bounded task queues or worker pools within the Tokio runtime to limit concurrent task execution.
      • Task Prioritization (Tokio): If possible, prioritize critical Tokio tasks.
      • Resource Monitoring (Tokio): Monitor Tokio-specific metrics (e.g., task queue lengths, worker thread utilization) using tools like tokio-console.
      • Timeouts (Tokio): Use tokio::time::timeout to prevent individual Tokio tasks from running indefinitely.

Attack Surface: Unsafe Code Vulnerabilities (Tokio Internals)

  • Description: Bugs in Tokio's internal unsafe code (used for performance) could lead to memory safety issues. This is intrinsic to Tokio itself.
    • How Tokio Contributes: Tokio itself contains the unsafe code. This is not a consequence of using Tokio, but a property of Tokio's implementation.
    • Example: A hypothetical buffer overflow in Tokio's I/O handling due to incorrect unsafe pointer manipulation within the Tokio codebase.
    • Impact: Memory corruption, potentially leading to arbitrary code execution (worst case).
    • Risk Severity: Critical (potential for complete system compromise).
    • Mitigation Strategies:
      • Keep Tokio Updated: This is the primary mitigation. Regularly update to the latest Tokio version to receive security patches.
      • Avoid Custom unsafe Interactions: Do not write custom unsafe code that interacts with Tokio's internal data structures.
      • Rely on Tokio Maintainers: Trust the Tokio team's expertise in unsafe code.