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attack-surface.md

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Attack Surface Analysis for adam-p/markdown-here

Attack Surface: Cross-Site Scripting (XSS)

  • Description: Injection of malicious JavaScript code into the rendered HTML output, allowing the attacker to execute arbitrary code in the context of the victim's browser. This is the most significant direct risk.
    • How markdown-here Contributes: markdown-here is the direct mechanism for this attack. Its primary function is to convert Markdown to HTML. If its sanitization fails (due to misconfiguration, bypass, or an internal bug), it becomes the conduit for injecting malicious code.
    • Example:
      • html: true Misconfiguration: If the application sets html: true in the markdown-here configuration, an attacker can directly inject HTML, including <script> tags: <script>alert('XSS');</script>.
      • Sanitization Bypass (Hypothetical): A cleverly crafted, deeply nested Markdown structure that exploits a bug in the parser, causing it to generate unintended HTML tags that bypass sanitization (e.g., a sequence of characters that trick the parser into thinking a <script> tag is legitimate). This is less likely with a well-maintained library but represents the core risk.
      • Malicious Link (with weak link sanitization): [Click Here](javascript:alert('XSS')) - If markdown-here's link sanitization is disabled or improperly configured, this allows direct injection of javascript: URIs.
    • Impact:
      • Stealing user cookies and session tokens.
      • Redirecting users to malicious websites.
      • Defacing the application.
      • Keylogging and capturing user input.
      • Performing actions on behalf of the user (e.g., posting messages, changing settings).
    • Risk Severity: Critical
    • Mitigation Strategies:
      • Strictly Use Default Configuration: Never enable the html option unless you have an extremely well-justified reason and implement additional, robust server-side sanitization. The default html: false setting is crucial.
      • Defense-in-Depth (Server-Side Validation): Implement server-side input validation to reject any input containing suspicious characters or patterns (e.g., <, >, script, javascript:). This is a critical secondary defense.
      • Content Security Policy (CSP): Implement a strict CSP, ideally script-src 'self', to prevent the execution of injected scripts even if they bypass sanitization. This is a very strong mitigation.
      • Output Encoding: Ensure the output of markdown-here is properly HTML-encoded before being displayed in the browser. This prevents the browser from misinterpreting any remaining potentially malicious characters.
      • Regular Updates: Keep markdown-here updated to the latest version to benefit from any security patches related to sanitization or parser bugs.
      • Avoid Custom Renderers: Do not override the default rendering behavior unless absolutely necessary. If you must use custom renderers, subject them to extremely rigorous security auditing.
      • Sanitize rendered output: Even with markdown-here sanitization, it is good practice to sanitize output using HTML sanitization library.

Attack Surface: Iframe src attribute manipulation

  • Description: Injection of malicious URL into src attribute of iframe HTML output, allowing the attacker to execute arbitrary code in the context of the victim's browser or redirect user to malicious website.
    • How markdown-here Contributes: markdown-here is the direct mechanism for this attack. If its sanitization fails (due to misconfiguration, bypass, or an internal bug), it becomes the conduit for injecting malicious URL.
    • Example:
      • html: true Misconfiguration: If the application sets html: true in the markdown-here configuration, an attacker can directly inject HTML, including <iframe> tags: <iframe src="javascript:alert('xss')"></iframe>.
      • Sanitization Bypass (Hypothetical): A cleverly crafted, Markdown structure that exploits a bug in the parser, causing it to generate unintended HTML tags that bypass sanitization.
    • Impact:
      • Stealing user cookies and session tokens.
      • Redirecting users to malicious websites.
      • Defacing the application.
      • Keylogging and capturing user input.
      • Performing actions on behalf of the user (e.g., posting messages, changing settings).
    • Risk Severity: High
    • Mitigation Strategies:
      • Strictly Use Default Configuration: Never enable the html option unless you have an extremely well-justified reason and implement additional, robust server-side sanitization. The default html: false setting is crucial.
      • Defense-in-Depth (Server-Side Validation): Implement server-side input validation to reject any input containing suspicious characters or patterns. This is a critical secondary defense.
      • Content Security Policy (CSP): Implement a strict CSP, to prevent the execution of injected scripts even if they bypass sanitization. This is a very strong mitigation.
      • Output Encoding: Ensure the output of markdown-here is properly HTML-encoded before being displayed in the browser. This prevents the browser from misinterpreting any remaining potentially malicious characters.
      • Regular Updates: Keep markdown-here updated to the latest version to benefit from any security patches related to sanitization or parser bugs.
      • Avoid Custom Renderers: Do not override the default rendering behavior unless absolutely necessary. If you must use custom renderers, subject them to extremely rigorous security auditing.
      • Sanitize rendered output: Even with markdown-here sanitization, it is good practice to sanitize output using HTML sanitization library.