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Attack Surface Analysis for chartjs/chart.js

Attack Surface: Cross-Site Scripting (XSS) via Untrusted Data (Labels, Tooltips, Legends)

  • 1. Cross-Site Scripting (XSS) via Untrusted Data (Labels, Tooltips, Legends)

    • Description: Injection of malicious JavaScript code into the chart's rendered output through data used for labels, tooltips, legends, or other text-based elements.
    • How Chart.js Contributes: Chart.js renders user-provided data into the chart. While it performs some escaping, it's not a comprehensive HTML sanitizer, especially for custom HTML content. The library's primary focus is on chart rendering, not robust input sanitization. This is a direct involvement because the vulnerability arises from how Chart.js handles and renders the provided data.
    • Example: An attacker provides a dataset where a label contains <script>alert('XSS')</script>. If this is not properly escaped before being passed to Chart.js, the script will execute when the chart is rendered.
    • Impact: Compromise of user accounts, data theft, session hijacking, website defacement, phishing attacks.
    • Risk Severity: High (Potentially Critical if user input directly controls callback functions or custom HTML).
    • Mitigation Strategies:
      • Input Validation and Sanitization: Rigorously validate and sanitize all data before passing it to Chart.js. Use a dedicated HTML sanitization library (like DOMPurify) if you allow any HTML in labels, tooltips, etc. Simple escaping might not be sufficient.
      • Content Security Policy (CSP): Implement a strict CSP to limit the execution of inline scripts.
      • Encode Data Appropriately: Use appropriate encoding functions.
      • Avoid Custom HTML if Possible: If you don't need custom HTML, don't use it.
      • Whitelist Allowed Characters/Tags: If you must allow some HTML, use a whitelist approach.

Attack Surface: XSS via Malicious Configuration Options (Specifically Callbacks)

  • 2. XSS via Malicious Configuration Options (Specifically Callbacks)

    • Description: Exploiting configuration options that allow specifying JavaScript callback functions. If user input can influence these callbacks, attackers can inject malicious code.
    • How Chart.js Contributes: Chart.js directly provides and executes these callback functions as part of its configuration API. This is the core of the vulnerability. The attacker's code runs within the context of Chart.js's execution.
    • Example: An attacker manipulates a URL parameter that is used to construct a tooltip callback: options.plugins.tooltip.callbacks.label = function(context) { return eval(urlParam); }. If urlParam contains malicious code, Chart.js will execute it.
    • Impact: Similar to standard XSS: account compromise, data theft, session hijacking, etc.
    • Risk Severity: Critical.
    • Mitigation Strategies:
      • Avoid User Input in Callbacks: Never allow user input to directly control the code within callback functions. This is paramount.
      • Whitelist Allowed Values: If user input must influence callback behavior, use a strict whitelist.
      • Indirect Control: Allow users to select from predefined options that indirectly control the callback's behavior, not provide code directly.