attack-surface.md

Attack Surface Analysis for tokio-rs/tokio

Attack Surface: Unbounded Connection Handling

• Description: An attacker can overwhelm the server by establishing a massive number of connections, exceeding resource limits and causing denial of service.
• Tokio Contribution: Tokio's efficient TcpListener and asynchronous networking are designed for high concurrency, making it easy to handle a large number of connections, but also amplifying the impact if connection limits are not enforced.
• Example: A botnet floods a Tokio-based web server with connection requests, exhausting server memory and CPU, making the server unresponsive to legitimate users.
• Impact: Denial of Service (DoS), service unavailability.
• Risk Severity: High
• Mitigation Strategies:
  • Implement connection limits at the application level using Tokio's APIs or external libraries.
  • Utilize operating system level connection limits (e.g., ulimit).
  • Employ connection rate limiting and throttling middleware or custom logic within the Tokio application.
  • Leverage load balancers or reverse proxies with connection limits in front of the Tokio application.

Attack Surface: Unbounded Task Spawning

• Description: Malicious input or actions trigger the creation of an excessive number of Tokio tasks, overwhelming the runtime scheduler and resources, leading to denial of service or performance degradation.
• Tokio Contribution: Tokio's tokio::spawn and task management features are designed for efficient concurrency, but uncontrolled task spawning can become a critical DoS vector if not managed properly.
• Example: A user repeatedly submits requests that each spawn a new Tokio task without proper queuing or limits. This leads to task queue exhaustion, scheduler overload, and ultimately application unresponsiveness.
• Impact: Denial of Service (DoS), severe performance degradation, application instability, potential for complete service outage.
• Risk Severity: High
• Mitigation Strategies:
  • Implement task queuing and rate limiting mechanisms to control task creation within the Tokio application.
  • Use bounded channels for communication between tasks to apply backpressure and limit task backlog.
  • Carefully design application logic to avoid spawning tasks directly in response to untrusted external input without validation and control.
  • Monitor task queue length and Tokio runtime resource consumption to detect and respond to potential task spawning attacks.

Attack Surface: Memory Exhaustion via Buffering

• Description: Attackers send large amounts of data designed to fill up buffers used by Tokio's asynchronous operations (network streams, channels), leading to memory exhaustion and application crashes, causing denial of service.
• Tokio Contribution: Tokio's asynchronous networking and channel implementations rely on buffering data for efficiency. If buffer sizes are not bounded or backpressure is not handled correctly in Tokio applications, it becomes a high-risk vulnerability. Components like BytesMut, mpsc channels, and network streams are relevant.
• Example: An attacker sends extremely large messages to a Tokio-based server, filling up receive buffers managed by Tokio and causing the application to run out of memory and crash.
• Impact: Denial of Service (DoS), application crash, complete service outage, potential for data corruption if memory exhaustion leads to unpredictable behavior before crashing.
• Risk Severity: High
• Mitigation Strategies:
  • Set explicit limits on buffer sizes when configuring network operations and channels within the Tokio application.
  • Implement backpressure mechanisms using Tokio's streams and channels to control data flow and prevent buffer overflows.
  • Use bounded channels with fixed capacities to limit memory usage for inter-task communication.
  • Validate and sanitize input data to prevent processing excessively large payloads that could trigger buffer exhaustion.

Attack Surface: Deadlocks due to Asynchronous Primitives

• Description: Improper and complex usage of Tokio's asynchronous synchronization primitives (like Mutex, Semaphore, channels) can lead to deadlocks, where tasks become blocked indefinitely, causing complete application unresponsiveness and denial of service.
• Tokio Contribution: Tokio provides asynchronous versions of common synchronization primitives that are essential for concurrent programming. However, incorrect usage, especially in intricate asynchronous workflows built with Tokio, can introduce deadlock vulnerabilities.
• Example: Two or more tasks in a Tokio application become mutually blocked while waiting for each other to release asynchronous mutexes or send/receive on channels, resulting in a deadlock and complete application freeze.
• Impact: Denial of Service (DoS), application unresponsiveness, complete service outage, requiring application restart to recover.
• Risk Severity: High
• Mitigation Strategies:
  • Carefully design asynchronous workflows to avoid circular dependencies and complex locking patterns when using Tokio's synchronization primitives.
  • Employ timeouts with asynchronous operations (e.g., tokio::time::timeout) to prevent indefinite blocking and allow for error handling in case of potential deadlocks.
  • Thoroughly test asynchronous code paths, especially those involving synchronization, to identify and eliminate potential deadlocks.
  • Simplify asynchronous logic and reduce the complexity of synchronization where possible to minimize the risk of deadlocks.

Attack Surface: Vulnerabilities in Tokio Dependencies

• Description: Security vulnerabilities in Tokio's dependencies (crates it relies upon, such as mio, polling, etc.) can indirectly and critically affect applications using Tokio.
• Tokio Contribution: Tokio, like any software library, depends on other crates. Vulnerabilities in these dependencies are inherited by Tokio-based applications, making it a critical supply chain risk.
• Example: A critical vulnerability is discovered in the mio crate, a core dependency of Tokio, allowing for remote code execution. Applications using Tokio are now indirectly vulnerable to this critical flaw through the dependency.
• Impact: Wide range of critical impacts depending on the nature of the dependency vulnerability, including Remote Code Execution (RCE), Denial of Service (DoS), privilege escalation, and information disclosure.
• Risk Severity: Critical (depending on the specific dependency vulnerability)
• Mitigation Strategies:
  • Regularly audit and update Tokio dependencies using tools like cargo update and cargo audit.
  • Utilize dependency scanning tools and services to proactively identify known vulnerabilities in Tokio's dependency tree.
  • Monitor security advisories and vulnerability databases for Tokio and its dependencies to stay informed about potential risks.
  • Consider using dependency management tools and practices that promote reproducible builds and facilitate timely updates to patched versions of dependencies.