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attack-surface.md

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Attack Surface Analysis for ffmpegwasm/ffmpeg.wasm

Attack Surface: Maliciously Crafted Media Files

  • Description: Exploiting vulnerabilities within FFmpeg's media processing components (demuxers, decoders, parsers) by providing specially crafted media files.
  • ffmpeg.wasm Contribution: ffmpeg.wasm utilizes the FFmpeg library for media processing, inherently inheriting all of FFmpeg's parsing and decoding logic, including potential vulnerabilities.
  • Example: A user uploads a TIFF image file engineered to trigger a heap buffer overflow in FFmpeg's TIFF decoder when processed by ffmpeg.wasm.
  • Impact:
    • Denial of Service (DoS): Application instability, crashes, or becoming unresponsive due to resource exhaustion or errors within ffmpeg.wasm.
    • Memory Corruption: Potential for memory corruption within the WebAssembly sandbox, leading to unpredictable application behavior or further exploitation attempts.
    • Potentially Sandbox Escape (Low Probability, but Critical if Achieved): While WebAssembly is sandboxed, theoretical vulnerabilities could, in extremely rare cases, lead to a sandbox escape.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Strict Input Validation: Implement rigorous file type validation and sanitization before processing with ffmpeg.wasm. Validate file headers, magic numbers, and consider using dedicated libraries for file format validation prior to FFmpeg processing.
    • File Size Limits: Enforce strict limits on the maximum file size allowed for processing to mitigate resource exhaustion and potential DoS attacks.
    • Regular Updates of ffmpeg.wasm: Maintain ffmpeg.wasm at the latest version to incorporate crucial security patches and bug fixes from upstream FFmpeg.
    • Content Security Policy (CSP): Implement a restrictive CSP to limit the application's capabilities and reduce the potential impact of a successful exploit.
    • Sandboxing Reliance and Browser Updates: Depend on the browser's WebAssembly sandbox for isolation and ensure users are encouraged to keep their browsers updated to benefit from the latest sandbox security enhancements.

Attack Surface: Unvalidated Input Parameters to ffmpeg.wasm Commands

  • Description: Injecting malicious commands or arguments into the ffmpeg.wasm command line interface through user-controlled input that is improperly sanitized.
  • ffmpeg.wasm Contribution: The JavaScript API of ffmpeg.wasm allows developers to construct and execute FFmpeg commands using user-provided data. Insufficient input validation can lead to command injection vulnerabilities within the ffmpeg.wasm context.
  • Example: A user manipulates a filename parameter in a video conversion command, injecting special characters or arguments that could cause ffmpeg.wasm to perform unintended actions, such as attempting to access or process files outside the intended scope (within the sandbox limitations).
  • Impact:
    • Unexpected Behavior within ffmpeg.wasm: ffmpeg.wasm might execute unintended operations or produce unexpected outputs.
    • Denial of Service (DoS): Malicious commands could lead to excessive resource consumption or errors within ffmpeg.wasm, causing application instability or failure.
    • Information Disclosure (Limited): In specific scenarios, carefully crafted commands might reveal limited information about the processing environment or internal state, although constrained by the WebAssembly sandbox.
  • Risk Severity: High
  • Mitigation Strategies:
    • Robust Input Sanitization and Validation: Thoroughly sanitize and validate all user inputs that are used to construct ffmpeg.wasm commands. Employ allow-lists for permitted characters and formats, and strictly reject any unexpected or potentially malicious input.
    • Parameterization over String Concatenation: Utilize API features that allow for parameterization of commands instead of directly concatenating user input into command strings to minimize injection risks.
    • Principle of Least Privilege in Command Construction: Design the application to only execute the absolutely necessary FFmpeg commands and restrict the functionalities exposed to user control. Avoid providing users with direct or overly flexible command construction capabilities.
    • Command Auditing and Logging: Implement logging of all executed ffmpeg.wasm commands for debugging, security monitoring, and incident response purposes.

Attack Surface: Inherited Vulnerabilities from FFmpeg Library

  • Description: ffmpeg.wasm directly inherits security vulnerabilities that are present in the underlying native FFmpeg library from which it is compiled.
  • ffmpeg.wasm Contribution: As a port of FFmpeg, ffmpeg.wasm's security posture is fundamentally tied to the security of the FFmpeg codebase it is based upon. Any known vulnerabilities in the specific FFmpeg version used to build ffmpeg.wasm are likely to be present and exploitable.
  • Example: A publicly disclosed Remote Code Execution (RCE) vulnerability (CVE) exists in libavformat of FFmpeg version X. If ffmpeg.wasm is built using FFmpeg version X or an earlier vulnerable version, the ffmpeg.wasm instance will also be vulnerable to this RCE if triggered by a crafted media file.
  • Impact: Impacts are similar to "Maliciously Crafted Media Files" but specifically attributed to known vulnerabilities in the underlying FFmpeg library: Denial of Service, Memory Corruption, and potentially Sandbox Escape (though still low probability).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Prioritize Regular Updates of ffmpeg.wasm: It is paramount to consistently use the most recent ffmpeg.wasm releases. These updates are crucial as they typically incorporate security patches and address known CVEs from the upstream FFmpeg project.
    • Proactive Vulnerability Monitoring: Actively monitor FFmpeg security advisories, CVE databases (like NVD), and the ffmpeg.wasm project's release notes for information on newly discovered vulnerabilities and patches.
    • Consider Selective Feature Compilation (Advanced, with Caution): For highly security-sensitive applications, and if feasible, explore the possibility of compiling ffmpeg.wasm with a minimal set of required FFmpeg features. This advanced technique, if done correctly, could potentially reduce the attack surface by excluding less necessary and potentially vulnerable components. However, this is complex and requires deep FFmpeg knowledge and careful testing to avoid breaking functionality. Generally, staying updated is the more practical and recommended approach for most developers.