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Mitigation Strategies Analysis for asciinema/asciinema-player

Mitigation Strategy: Strict Input Sanitization and Validation (for asciicast content)

Description:

  1. Target asciinema-player Input: Focus specifically on the data passed to the asciinema-player (the asciicast JSON).
  2. ANSI Whitelist: Before passing data to asciinema-player, implement a strict whitelist of allowed ANSI escape sequences and control characters. This is crucial because asciinema-player renders terminal output, which can include potentially dangerous sequences.
  3. Dedicated Parser: Use (or create) a parser specifically designed for ANSI escape codes. This parser should:
    • Tokenize the asciicast data, separating text from escape sequences.
    • Validate each token against the whitelist.
    • Reject or sanitize any input containing non-whitelisted sequences.
    • Handle malformed sequences gracefully.
  4. Schema Validation: Validate the structure of the asciicast JSON against the expected schema before passing it to asciinema-player.
  5. Regular Updates: Regularly update the whitelist and parser to address new bypasses.
  6. Testing: Thoroughly test with various inputs, including malicious sequences and edge cases. Use fuzzing.

Threats Mitigated:

  • Cross-Site Scripting (XSS) (Severity: Critical): Malicious JavaScript within escape sequences could be executed. Sanitization prevents this.
  • Data Exfiltration (Severity: High): Escape sequences could trigger network requests or manipulate the DOM to steal data.
  • UI Redressing (Severity: Medium): Manipulation of the terminal display to overlay content.
  • Denial of Service (DoS) (Severity: Medium): Some DoS attacks are possible via malformed input.

Impact:

  • XSS: Risk reduced from Critical to Low.
  • Data Exfiltration: Risk reduced from High to Low.
  • UI Redressing: Risk reduced from Medium to Low.
  • DoS: Risk reduced from Medium to Low (for specific input-related DoS).

Currently Implemented: (Example - Replace with your project's status)

  • Basic HTML escaping is done before passing data to the player.
  • Schema validation is performed.

Missing Implementation: (Example - Replace with your project's status)

  • A dedicated ANSI escape code parser and whitelist are missing. This is the most critical gap.
  • Regular updates to sanitization logic are not automated.
  • Comprehensive testing (including fuzzing) is missing.

Mitigation Strategy: Configuration for Safe Defaults (within asciinema-player)

Description:

  1. Review asciinema-player Options: Thoroughly review all available configuration options for asciinema-player. Look for options related to:
    • Terminal size limits (rows, columns).
    • Font loading (disable if possible, or restrict sources).
    • Any options related to interactivity or external resource loading.
  2. Restrictive Configuration: Configure asciinema-player with the most restrictive settings possible, without breaking essential functionality. Prioritize security over features.
  3. Disable Unnecessary Features: If your application doesn't need certain features (e.g., specific terminal emulation modes), disable them if possible through configuration.
  4. Example: If the player has options to limit the maximum number of rows or columns, or to disable certain escape sequences, use them.

Threats Mitigated:

  • Denial of Service (DoS) (Severity: Medium): Limiting terminal size can prevent some DoS attacks.
  • Code Injection (Severity: Low): Disabling unnecessary features reduces the attack surface.
  • Information Disclosure (Severity: Low): Restricting font loading can prevent font-based fingerprinting.

Impact:

  • DoS: Risk reduced from Medium to Low (for specific DoS types).
  • Code Injection: Risk reduced from Low to Very Low.
  • Information Disclosure: Risk reduced from Low to Very Low.

Currently Implemented: (Example - Replace with your project's status)

  • Default asciinema-player configuration is used.

Missing Implementation: (Example - Replace with your project's status)

  • A thorough review of asciinema-player options and implementation of restrictive settings is needed.

Mitigation Strategy: Careful Handling of Player Events and Output

Description:

  1. Identify Events: Identify any events emitted by asciinema-player that your application handles (e.g., events related to user interaction, playback progress, or errors).
  2. Validate Event Data: Before using any data received from these events, rigorously validate and sanitize it. Treat this data as untrusted input.
  3. Output Sanitization: If your application extracts any text or data from the rendered output of asciinema-player (e.g., for copying to the clipboard), sanitize this output again before using it. Even if the initial asciicast data was sanitized, the player's rendering process could potentially introduce vulnerabilities.
  4. Example: If the player emits an event when the user copies text, and your application uses that copied text, sanitize the text before placing it on the clipboard or using it elsewhere.

Threats Mitigated:

  • Cross-Site Scripting (XSS) (Severity: Medium): If event data or extracted output is used to update the DOM, sanitization prevents XSS.
  • Data Exfiltration (Severity: Low): Sanitization prevents the use of event data for malicious purposes.

Impact:

  • XSS: Risk reduced from Medium to Low.
  • Data Exfiltration: Risk reduced from Low to Very Low.

Currently Implemented: (Example - Replace with your project's status)

  • The application handles the copy event from the player.

Missing Implementation: (Example - Replace with your project's status)

  • The copied text from the copy event is not sanitized before being used. This is a potential XSS vulnerability.