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threat-modeling.md

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Threat Model Analysis for adam-p/markdown-here

Threat: XSS via Malicious Script Injection in Link URLs

  • Description: An attacker crafts a Markdown link using a malicious javascript: URL or other dangerous URL schemes. Markdown Here's link parsing logic fails to properly sanitize these URLs, allowing the injected script to be executed in the victim's browser. Example: [Click Me](javascript:alert('XSS')).
    • Impact: Complete account compromise, data breaches, session hijacking, redirection to phishing sites, and other actions the user could perform.
    • Affected Component: Markdown Here's link parsing and rendering logic (likely within the core Markdown parsing module and potentially a URL sanitization function).
    • Risk Severity: Critical
    • Mitigation Strategies:
      • Strict URL Whitelisting (Post-Processing): After Markdown Here processes the input, use a dedicated URL parsing library to enforce a strict whitelist of allowed URL schemes (e.g., http, https, mailto). Reject any URL that doesn't match.
      • URL Sanitization Library (Post-Processing): Employ a robust URL sanitization library (e.g., from DOMPurify or a standalone library) after Markdown Here rendering to parse and validate URLs, handling encoding/decoding correctly.
      • CSP (script-src): Implement a strong Content Security Policy with a restrictive script-src directive to prevent the execution of inline JavaScript, even if a javascript: URL is injected.

Threat: XSS via Malicious Script Injection in Image URLs

  • Description: An attacker crafts a Markdown image tag with a malicious javascript: URL or other dangerous URL scheme in the src attribute. Markdown Here's image parsing logic fails to sanitize these URLs. Example: ![alt text](javascript:alert('XSS')).
    • Impact: Potentially the same as link-based XSS (account compromise, data breaches), although exploitation might be less reliable depending on the browser and rendering context.
    • Affected Component: Markdown Here's image parsing and rendering logic (likely a separate function or module from link handling, but potentially sharing sanitization routines).
    • Risk Severity: High
    • Mitigation Strategies:
      • Strict URL Whitelisting (Post-Processing): Apply the same strict URL whitelisting and sanitization strategies as for link URLs, using a dedicated library after Markdown Here processing.
      • Image Proxy (Optional): Consider using an image proxy to fetch and serve all images, isolating the application from potentially malicious image URLs.
      • CSP (script-src): A strong CSP with a restrictive script-src is crucial.

Threat: XSS via Malicious HTML Attributes

  • Description: If Markdown Here allows inline HTML or custom Markdown extensions that permit arbitrary HTML attributes, an attacker can inject malicious event handlers (e.g., onload, onerror). Markdown Here's sanitization (if any) fails to remove these attributes. Example: <img src="x" onerror="alert('XSS')">.
    • Impact: Execution of arbitrary JavaScript, leading to account compromise, data breaches, and other XSS consequences.
    • Affected Component: Markdown Here's HTML sanitization module (if it exists) or the lack thereof. The core Markdown parsing logic, which determines allowed HTML elements and attributes, is also directly involved.
    • Risk Severity: Critical
    • Mitigation Strategies:
      • Disable Inline HTML (Configuration): Configure Markdown Here to completely disable the rendering of inline HTML. This is the most secure option.
      • Strict HTML Sanitization (DOMPurify - Post-Processing): If inline HTML must be allowed, use a robust HTML sanitizer like DOMPurify after Markdown Here rendering. Configure DOMPurify with a very restrictive whitelist, disallowing all event handler attributes (on*).
      • CSP (script-src): A strong CSP with a restrictive script-src directive is essential to prevent the execution of inline event handlers.

Threat: XSS via Exploiting Parser Bugs

  • Description: An attacker discovers a vulnerability in Markdown Here's parsing engine (or the underlying Markdown library it uses) and crafts a specific Markdown input to trigger this bug, resulting in JavaScript injection. This could be a buffer overflow, a regular expression DoS leveraged for XSS, or an unexpected interaction between Markdown features.
    • Impact: Complete control over the user's session, data breaches, and all other consequences of XSS.
    • Affected Component: The core Markdown parsing engine within Markdown Here or its dependent Markdown library (e.g., marked, markdown-it).
    • Risk Severity: Critical
    • Mitigation Strategies:
      • Regular Updates: Keep Markdown Here and all of its dependencies (especially the Markdown parser) up-to-date. Monitor security advisories for all related projects.
      • Fuzz Testing: Perform fuzz testing on the Markdown rendering pipeline to try to trigger unexpected behavior.
      • HTML Sanitization (DOMPurify - Post-Processing): Even for parser bugs, a robust HTML sanitizer like DOMPurify after Markdown Here rendering provides a crucial last line of defense.
      • Defense in Depth: Combine multiple mitigation strategies (sanitization, CSP, input validation) for layered protection.