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attack-surface.md

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Attack Surface Analysis for kkuchta/css-only-chat

Attack Surface: CSS Complexity Denial of Service (DoS)

  • Description: Attackers exploit complex CSS selectors and calculations to overwhelm the browser's rendering engine, causing it to freeze or crash.
  • How css-only-chat contributes: The application's core functionality relies entirely on CSS for state management and updates, making it inherently vulnerable. Every user interaction triggers CSS re-calculations, and there's no JavaScript fallback to handle excessive load.
  • Example: An attacker sends a rapid series of messages, each designed to trigger a large number of CSS counter updates or force the evaluation of deeply nested selectors (e.g., using specially crafted usernames that interact with complex attribute selectors).
  • Impact: Denial of service for legitimate users; the chat application becomes completely unusable.
  • Risk Severity: Critical (renders the application unusable).
  • Mitigation Strategies:
    • Developer:
      • a. Implement strict rate limiting on all user actions that trigger CSS updates (message sending, status changes, etc.). This is the most crucial mitigation.
      • b. Limit the maximum length and complexity of user input (usernames, messages) to prevent crafting overly complex CSS selectors. Impose hard limits.
      • c. Radically simplify the CSS structure. Avoid deeply nested selectors, complex attribute selectors (especially with regular expressions), and excessive use of sibling combinators (+, ~). Prioritize simplicity over features.
      • d. Monitor server-side for patterns of rapid requests that could indicate a DoS attempt and implement IP-based blocking or throttling.
      • e. Use a CSS preprocessor for minification, but understand this is a minor optimization, not a primary defense.

Attack Surface: Information Disclosure via CSS State Inspection

  • Description: Attackers inspect the computed CSS styles or attribute values to infer information about other users or the application's internal state.
  • How css-only-chat contributes: The application's state (online status, message read status, etc.) is necessarily encoded within the CSS, making it directly visible to anyone who inspects the DOM using standard browser tools.
  • Example: An attacker uses browser developer tools to inspect the CSS rules applied to a user's element and observes an attribute like [data-status="online"] or a class like .user-online, revealing their online status. They can also track changes to these attributes to see when messages are read.
  • Impact: Loss of privacy; attackers can gather information about user activity and potentially use it for social engineering or other malicious purposes.
  • Risk Severity: High (privacy violation, potential for further attacks).
  • Mitigation Strategies:
    • Developer:
      • a. Avoid storing sensitive information directly in easily observable CSS attributes or class names. This is the core issue.
      • b. Use obfuscated or indirect representations of state. Instead of [data-online="true"], use a less obvious attribute, a combination of attributes, or a hashed/encoded value that is difficult to interpret without knowing the encoding scheme.
      • c. The most effective mitigation is to use JavaScript to manage state and dynamically update the CSS. This fundamentally changes the architecture but is the only way to truly prevent this type of information disclosure. Without JavaScript, any state information must be reflected in the CSS somehow.

Attack Surface: Layout Manipulation and Phishing

  • Description: Attackers exploit CSS rendering quirks or vulnerabilities to alter the visual presentation, creating deceptive interfaces or mimicking legitimate elements.
  • How css-only-chat contributes: The complete reliance on CSS for all visual aspects, including layout, positioning, and even dynamic updates, makes it highly susceptible to subtle manipulations. The lack of JavaScript-based validation or control increases the risk.
  • Example: An attacker discovers a browser-specific rendering bug that, when triggered by a specific combination of user inputs (e.g., a long username combined with a particular message), causes elements to overlap unexpectedly. This could obscure legitimate content or create a fake input field that overlays a real one.
  • Impact: Users could be tricked into entering credentials or sensitive information into a fake interface, leading to account compromise or data theft.
  • Risk Severity: High (potential for phishing and account compromise).
  • Mitigation Strategies:
    • Developer:
      • a. Extensive cross-browser testing is paramount. Test on a wide variety of browsers, versions, and operating systems to identify and address rendering inconsistencies.
      • b. Use a CSS reset or normalize stylesheet to minimize cross-browser differences.
      • c. Employ defensive CSS techniques. Explicitly set position, z-index, width, height, and other layout-related properties to prevent elements from being unintentionally repositioned or overlapped. Assume the CSS will be attacked.
      • d. Radically simplify the CSS layouts and interactions. Avoid complex or unusual CSS techniques. The simpler the CSS, the less likely it is to have exploitable quirks.
      • e. The most robust mitigation is to use JavaScript to manage layout and prevent unexpected CSS manipulations. This allows for dynamic validation and control that is impossible with pure CSS.