threat-modeling.md

Threat Model Analysis for bytecodealliance/wasmtime

Threat: Sandbox Escape via JIT Compiler Vulnerability

• Description: An attacker crafts a malicious WebAssembly module that exploits a vulnerability in Wasmtime's JIT (Just-In-Time) compiler. The module contains specially crafted code that, when compiled, triggers a bug (e.g., a buffer overflow, type confusion) in the JIT, leading to arbitrary code execution within the Wasmtime runtime's memory space. The attacker then uses this initial foothold to attempt to escape the sandbox and gain control of the host system.
  • Impact:
    • Complete compromise of the host system, allowing the attacker to execute arbitrary code with the privileges of the application running Wasmtime.
    • Data theft, modification, or deletion on the host system.
    • Potential for lateral movement to other systems on the network.
  • Affected Wasmtime Component: JIT Compiler (e.g., Cranelift), potentially interacting with the memory management and sandboxing mechanisms.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Mitigation: Keep Wasmtime updated to the latest stable release to receive security patches.
    • Mitigation: Implement strict input validation before passing data to the WebAssembly module (reduces the attack surface, though doesn't directly address a Wasmtime bug).
    • Mitigation: Use a separate process for each Wasmtime instance (if feasible) to limit the impact of a successful escape.
    • Mitigation: Employ a robust security monitoring system to detect and respond to unusual activity on the host system.

Threat: Resource Exhaustion via Infinite Loop (Wasmtime Scheduler/Engine)

• Description: An attacker provides a WebAssembly module containing an infinite loop (or a very long-running loop) without yielding control. This consumes excessive CPU cycles within the Wasmtime instance, specifically exploiting weaknesses in Wasmtime's ability to preempt or limit execution. This differs from a simple infinite loop; it targets a failure in Wasmtime's resource management.
  • Impact:
    • Denial of Service (DoS) of the Wasmtime instance, making it unresponsive.
    • If other modules are running in the same instance, they are also affected.
    • Potential impact on the host application if it relies on the Wasmtime instance for critical functionality.
  • Affected Wasmtime Component: Wasmtime's execution engine and scheduler. The vulnerability lies in Wasmtime's failure to enforce limits effectively.
  • Risk Severity: High
  • Mitigation Strategies:
    • Mitigation: Keep Wasmtime updated to the latest stable release. This is crucial as it addresses potential scheduler bugs.
    • Mitigation: Configure Wasmtime's instruction limit (fuel metering) to restrict the number of instructions a module can execute. Ensure this mechanism is correctly enforced by Wasmtime.
    • Mitigation: Implement timeouts for WebAssembly module execution within the host application, acting as a secondary defense.
    • Mitigation: Monitor CPU usage of Wasmtime instances and take action (e.g., terminate the instance) if limits are exceeded.

Threat: Memory Exhaustion via Large Allocation (Wasmtime Memory Management)

• Description: An attacker crafts a WebAssembly module that attempts to allocate a very large amount of memory within the Wasmtime sandbox. The threat here is a failure in Wasmtime's memory management to correctly enforce limits, allowing the allocation to succeed beyond expected bounds.
  • Impact:
    • Denial of Service (DoS) of the Wasmtime instance. The instance may crash or become unresponsive due to Wasmtime's internal memory management failure.
    • Potential impact on the host application if it relies on the Wasmtime instance.
  • Affected Wasmtime Component: Wasmtime's memory management system. The vulnerability is in Wasmtime's failure to enforce configured limits.
  • Risk Severity: High
  • Mitigation Strategies:
    • Mitigation: Keep Wasmtime updated to the latest stable release to address potential memory management bugs.
    • Mitigation: Configure strict memory limits for Wasmtime instances using the Config::memory_size or related settings. Verify that these limits are correctly enforced by Wasmtime.
    • Mitigation: Monitor memory usage of Wasmtime instances and take action if limits are approached or exceeded.

Threat: Integer Overflow leading to Sandbox Escape (Wasmtime Internals)

• Description: An attacker crafts a WebAssembly module that, through carefully constructed input or operations, triggers an integer overflow within Wasmtime's internal code (e.g., during bounds checking, memory allocation calculations, or within the JIT compiler). This overflow leads to a vulnerability that allows the attacker to bypass sandbox restrictions and potentially gain arbitrary code execution. This is distinct from an overflow within the WebAssembly module itself; it must be within Wasmtime's code.
  • Impact:
    • Potentially exploitable vulnerabilities, leading to a sandbox escape and arbitrary code execution on the host system.
    • Unpredictable behavior of the Wasmtime instance.
  • Affected Wasmtime Component: Wasmtime's internal components that perform arithmetic operations, including memory management, the JIT compiler, and potentially WASI implementations (if the vulnerability is in shared code).
  • Risk Severity: High to Critical (depending on the exploitability of the overflow)
  • Mitigation Strategies:
    • Mitigation: Keep Wasmtime updated to the latest stable release. This is the primary defense.
    • Mitigation: Fuzz testing of the Wasmtime API surface can help identify potential integer overflow vulnerabilities within Wasmtime.