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Threat Model Analysis for ffmpegwasm/ffmpeg.wasm

Threat: FFmpeg Codec Input Validation Vulnerability

Description: An attacker provides a maliciously crafted media file that exploits a parsing vulnerability within a specific FFmpeg codec (e.g., libavcodec, libavformat) used by ffmpeg.wasm. This vulnerability is triggered during the decoding process. Exploitation could involve sending a specially crafted video or image file via user upload or other input mechanisms. Impact: Browser tab crash, unexpected application behavior, potential memory corruption within the WASM environment. In a worst-case scenario (though less likely within the WASM sandbox), it could theoretically lead to remote code execution if a vulnerability allows escaping the WASM sandbox. Information disclosure is also a potential impact if memory contents are leaked. Affected ffmpeg.wasm component: Specific FFmpeg codecs (e.g., H.264 decoder, MP3 decoder, image decoders) within the ffmpeg.wasm module. Risk Severity: High Mitigation Strategies:

  • Prioritize using the latest stable version of ffmpeg.wasm: This ensures you benefit from the most recent security patches from the upstream FFmpeg project. Regularly update ffmpeg.wasm.
  • Implement robust input sanitization and validation: While challenging to fully validate complex media formats client-side, perform basic checks like file type validation and consider using server-side validation or pre-processing before client-side processing with ffmpeg.wasm.
  • Implement comprehensive error handling: Wrap ffmpeg.wasm operations in try-catch blocks and implement error handling to gracefully manage exceptions and prevent application crashes when encountering malformed input.
  • Limit supported media formats: Reduce the attack surface by only supporting necessary media formats and codecs. Avoid enabling support for obscure or less-tested formats if they are not essential for your application's functionality.

Threat: Client-Side CPU Exhaustion DoS

Description: An attacker intentionally provides a very large or computationally complex media file, or a series of such files, to the application. Processing these files using ffmpeg.wasm consumes excessive CPU resources on the user's machine. This can lead to the browser tab becoming unresponsive, freezing, or crashing, effectively denying service to the user. An attacker might automate uploads of such files to repeatedly disrupt service for targeted users. Impact: Denial of Service for the user, browser slowdown, application unresponsiveness, negative user experience. For users with limited resources, this can be a significant disruption. Affected ffmpeg.wasm component: Core ffmpeg.wasm module performing media processing (encoding, decoding, filtering, etc.). Risk Severity: High Mitigation Strategies:

  • Implement strict client-side file size limits: Restrict the maximum size of media files that can be processed by ffmpeg.wasm.
  • Implement client-side processing time limits and timeouts: Set a maximum execution time for ffmpeg.wasm operations. If processing exceeds this time, terminate the operation and inform the user.
  • Provide clear user feedback and progress indicators: Inform users about the processing time and resource usage. This helps manage expectations and allows users to stop long-running processes if needed.
  • Consider server-side processing for critical or resource-intensive operations: For functionalities where DoS is a major concern, offload the most computationally demanding tasks to a server-side component with better resource management and monitoring capabilities.
  • Implement rate limiting: If user uploads are involved, implement rate limiting to prevent a single user from overwhelming the client-side processing capabilities with numerous large files in a short period.