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attack-surface.md

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Attack Surface Analysis for markedjs/marked

Attack Surface: Cross-Site Scripting (XSS) via Markdown Injection

  • Description: Attackers inject malicious JavaScript code by crafting specific Markdown input that, when parsed and rendered by marked.js, results in the execution of the script in a user's browser.
  • How Marked Contributes: marked.js's primary function is to convert Markdown to HTML. If sanitization is not enabled or is insufficient, it can render malicious HTML tags like <script> or event attributes injected within Markdown, leading to XSS.
  • Example:
    • Markdown Input: `<img src="x" onerror="alert('XSS')">`
    • Rendered HTML (if unsanitized): `<img src="x" onerror="alert('XSS')">`
    • Result: When a user's browser renders this HTML, the JavaScript alert('XSS') will execute.
  • Impact:
    • Account takeover
    • Data theft
    • Malware distribution
    • Website defacement
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Enable and Configure Sanitization: Utilize marked.js's built-in sanitization options (if available and robust) or integrate a dedicated and well-vetted HTML sanitization library (like DOMPurify) after marked.js rendering but before displaying the HTML to users.
    • Strict Sanitization Rules: Configure the sanitizer to aggressively remove or neutralize potentially harmful HTML tags, attributes, and URL schemes. Focus on blocking tags like script, iframe, object, embed, and event attributes like onerror, onload, onmouseover, as well as dangerous URL schemes like javascript: .
    • Content Security Policy (CSP): Implement a strict CSP to control the sources from which the browser is allowed to load resources. This acts as a strong secondary defense layer against XSS, even if sanitization is bypassed.

Attack Surface: HTML Injection (Beyond Scripting)

  • Description: Attackers inject arbitrary HTML elements (beyond just <script>) through Markdown, leading to unintended modifications of the webpage's content and potentially enabling phishing or clickjacking attacks.
  • How Marked Contributes: marked.js renders various HTML tags from Markdown. Even if script execution is prevented, the rendering of other HTML elements can be exploited for malicious purposes if not properly controlled.
  • Example:
    • Markdown Input: `<iframe src="https://malicious-phishing-site.com" width="800" height="600"></iframe>`
    • Rendered HTML (if unsanitized): `<iframe src="https://malicious-phishing-site.com" width="800" height="600"></iframe>`
    • Result: An iframe embedding a malicious phishing site is displayed within the application, potentially tricking users into entering credentials or sensitive information on the attacker's site.
  • Impact:
    • Phishing attacks
    • Website defacement
    • Clickjacking
    • Redirection to malicious websites
  • Risk Severity: High
  • Mitigation Strategies:
    • Strict Whitelist-Based Sanitization: Configure marked.js or a separate sanitizer to use a strict whitelist approach for allowed HTML tags and attributes. Only permit tags and attributes that are absolutely necessary for the intended Markdown functionality. Deny by default and explicitly allow only safe elements.
    • Remove Potentially Dangerous Tags: Specifically remove tags like iframe, object, embed, form, base, and meta unless absolutely necessary and carefully controlled.
    • Content Security Policy (CSP): CSP can be configured to restrict the embedding of external resources, further mitigating the risk of HTML injection, especially iframes.

Attack Surface: Incorrect Sanitization Configuration

  • Description: Even when sanitization is implemented, improper or insufficient configuration of the sanitization mechanism used with marked.js can create vulnerabilities, allowing attackers to bypass the intended security measures and inject malicious HTML.
  • How Marked Contributes: marked.js relies on external sanitization if it's not built-in or if the built-in sanitization is not robust enough. Misconfiguring this external sanitization directly undermines the security intended when using marked.js to render user content.
  • Example:
    • Scenario: Sanitization is enabled, but it only blocks <script> tags and common event attributes, but fails to sanitize less common XSS vectors or bypass techniques.
    • Markdown Input: `<details open ontoggle=alert('XSS')>` (Example of a less common event attribute bypass)
    • Rendered HTML (if poorly sanitized): `<details open ontoggle=alert('XSS')>`
    • Result: The ontoggle event handler is not sanitized, leading to JavaScript execution when the <details> element is toggled.
  • Impact:
    • XSS and HTML injection vulnerabilities due to ineffective sanitization, negating the intended security benefits.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Thorough Testing of Sanitization: Rigorously test the sanitization configuration with a wide range of known XSS and HTML injection payloads and bypass techniques. Use automated testing tools and manual security reviews.
    • Regularly Update Sanitization Rules: Stay informed about new XSS bypass techniques and update sanitization rules and libraries accordingly. Security is an ongoing process, and sanitization rules need to evolve to remain effective.
    • Security Audits and Code Reviews: Conduct regular security audits and code reviews of the sanitization implementation and configuration to identify potential weaknesses and misconfigurations.
    • Prefer Well-Established Sanitization Libraries: Opt for well-established, actively maintained, and security-focused HTML sanitization libraries (like DOMPurify) over relying on potentially less robust or less frequently updated built-in sanitization options, if available in marked.js. Ensure the chosen library is configured correctly and securely.