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Threat Model Analysis for ruffle-rs/ruffle

Threat: Arbitrary Code Execution via AS3 Emulation Bug

  • Description: An attacker crafts a malicious SWF file that exploits a bug in Ruffle's ActionScript 3 interpreter. The bug could be a buffer overflow, type confusion, use-after-free, or logic error in how AS3 bytecode is handled. The attacker carefully constructs the bytecode to trigger the vulnerability and execute arbitrary code within the Ruffle sandbox.
  • Impact: Complete control over the Ruffle execution environment. Potentially, this could lead to a sandbox escape, allowing the attacker to execute arbitrary JavaScript in the context of the hosting page (XSS), steal cookies, or interact with other browser APIs.
  • Affected Ruffle Component: core crate, specifically the AS3 interpreter (avm2 module), bytecode handling functions, and potentially garbage collection routines.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Fuzzing: Continuous fuzzing of the AS3 interpreter with a wide variety of valid and invalid SWF inputs.
    • Code Audits: Regular security audits of the avm2 module, focusing on memory safety and correct bytecode handling.
    • Sandboxing: Strengthen the WebAssembly sandbox to make escape more difficult.
    • Type Safety: Leverage Rust's type system to prevent type confusion vulnerabilities.
    • Bounds Checking: Ensure rigorous bounds checking on all array and buffer accesses.

Threat: Denial of Service via Resource Exhaustion

  • Description: An attacker creates a SWF file designed to consume excessive CPU or memory within Ruffle. This could involve infinite loops, deeply nested function calls, allocation of large objects, or exploiting inefficiencies in Ruffle's rendering engine.
  • Impact: The browser tab running Ruffle becomes unresponsive, potentially affecting the entire browser. The user's experience is disrupted.
  • Affected Ruffle Component: core crate (AS3 interpreter, rendering engine), web crate (resource management).
  • Risk Severity: High
  • Mitigation Strategies:
    • Resource Limits: Implement strict limits on CPU time, memory allocation, and the number of nested function calls allowed within Ruffle.
    • Timeouts: Set timeouts for ActionScript execution to prevent infinite loops.
    • Monitoring: Monitor Ruffle's resource usage and terminate execution if limits are exceeded.
    • Efficient Algorithms: Optimize Ruffle's code to minimize resource consumption.

Threat: Sandbox Escape via ExternalInterface Emulation

  • Description: An attacker crafts a SWF that exploits a vulnerability in Ruffle's emulation of Flash's ExternalInterface API. The vulnerability could allow the SWF to pass malicious JavaScript code to the hosting page, bypassing the sandbox. This might involve incorrect validation of arguments or improper escaping of data.
  • Impact: Cross-site scripting (XSS) in the context of the hosting page. The attacker can execute arbitrary JavaScript, steal cookies, deface the page, or redirect the user to a malicious website.
  • Affected Ruffle Component: core crate (avm1 and avm2 modules, ExternalInterface implementation), web crate (communication with JavaScript).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Strict Input Validation: Rigorously validate all data received from the SWF through the emulated ExternalInterface.
    • Output Encoding: Properly encode any data passed from Ruffle to the hosting page's JavaScript.
    • Content Security Policy (CSP): Use CSP to restrict the types of actions that JavaScript can perform on the hosting page.
    • Limited API: Expose only the minimum necessary functionality to the SWF through ExternalInterface. Avoid exposing any sensitive APIs.

Threat: Memory Corruption via unsafe Code

  • Description: An attacker crafts a SWF that triggers a bug in one of Ruffle's unsafe code blocks. This could involve exploiting a race condition, use-after-free, or other memory safety violation within the unsafe code.
  • Impact: Potentially arbitrary code execution within the Ruffle sandbox, leading to a sandbox escape or denial of service.
  • Affected Ruffle Component: Any component that uses unsafe code (e.g., core, web, desktop). Specific functions and modules will vary depending on the vulnerability.
  • Risk Severity: High
  • Mitigation Strategies:
    • Minimize unsafe: Reduce the use of unsafe code to the absolute minimum.
    • Code Audits: Thoroughly audit all unsafe code blocks for memory safety vulnerabilities.
    • Mir: Use Miri (Rust's experimental MIR interpreter) to detect undefined behavior in unsafe code during testing.
    • Formal Verification: Consider using formal verification techniques to prove the correctness of critical unsafe code.

Threat: SWF Parsing Vulnerability

  • Description: An attacker creates a malformed SWF file that exploits a bug in Ruffle's SWF parser. This could involve overflowing buffers, triggering integer overflows, or exploiting other parsing errors.
  • Impact: Arbitrary code execution or denial of service.
  • Affected Ruffle Component: core crate (SWF parser).
  • Risk Severity: High
  • Mitigation Strategies:
    • Fuzzing: Extensively fuzz the SWF parser with a wide variety of malformed SWF files.
    • Robust Parsing Library: Use a well-tested and secure parsing library.
    • Memory Safety: Ensure that the parser is written in a memory-safe way, even when handling malformed input.

Threat: AS2/AS1 Emulation Vulnerabilities

  • Description: Similar to the AS3 threat, but targeting older ActionScript versions. An attacker crafts a malicious SWF file exploiting bugs in Ruffle's AS1/AS2 interpreter.
  • Impact: Arbitrary code execution within the Ruffle sandbox, potentially leading to sandbox escape, denial of service, or information disclosure.
  • Affected Ruffle Component: core crate, specifically the AS1/AS2 interpreter (avm1 module).
  • Risk Severity: High
  • Mitigation Strategies:
    • Fuzzing: Continuous fuzzing of the AS1/AS2 interpreter.
    • Code Audits: Regular security audits of the avm1 module.
    • Sandboxing: Strengthen the WebAssembly sandbox.
    • Prioritize AS3: If possible, encourage users to use AS3 content, as it is generally more secure and better supported by Ruffle.