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Attack Surface Analysis for daneden/animate.css

Attack Surface: CSS Injection (Indirect, via Class Name Manipulation) - Refined for Direct Involvement

  • Description: An attacker injects malicious CSS by manipulating the class names specifically provided by animate.css that are applied to elements. This exploits vulnerabilities in how the application handles user input that is used to select or construct animate.css class names. The attack requires the presence of animate.css and its class-based system.
  • animate.css Contribution: animate.css's core functionality relies on applying pre-defined class names to trigger animations. If the application allows user input to directly or indirectly control which animate.css classes are used, without proper sanitization, this creates the injection vector. The attacker is leveraging the specific class names defined by the library.
  • Example: An application allows users to choose an animation from a dropdown list. The dropdown values are directly used to construct the class name applied to an element (e.g., <div class="animate__animated animate__${userChoice}">). If a user can manipulate the userChoice value (e.g., through a modified request), they can inject arbitrary CSS by providing a value like: bounce; } #someElement { color: red; } .animate__fadeIn {. The attacker is specifically targeting the animate__ prefixed classes.
  • Impact: Allows the attacker to inject arbitrary CSS, potentially leading to defacement, data exfiltration (though difficult via CSS alone), or phishing attacks by altering the appearance of the page. The attacker can modify the styling and behavior of the page, potentially leading to a compromise of user data or trust.
  • Risk Severity: High (if user input directly or indirectly affects animate.css class names without rigorous sanitization).
  • Mitigation Strategies:
    • Strict Input Validation and Sanitization (Whitelist Approach): Never directly use user input to construct animate.css class names. Implement a strict whitelist of allowed animate.css class names (e.g., ['animate__bounce', 'animate__fadeIn', 'animate__fadeOut']). Reject any input that does not exactly match an entry in the whitelist. Do not attempt to "sanitize" by removing dangerous characters; instead, only allow known-good values.
    • Lookup Table/Mapping: Use a server-side lookup table or mapping to translate user-friendly input (e.g., "Fade In") into the corresponding safe animate.css class name (e.g., animate__fadeIn). This completely separates user input from the actual class name used.
    • Content Security Policy (CSP): A strong CSP with a restrictive style-src directive is crucial. This limits the impact of CSS injection, even if class name manipulation occurs. Example: 
      Content-Security-Policy: style-src 'self' cdn.jsdelivr.net;
      (Assuming animate.css is loaded from cdn.jsdelivr.net). This prevents the execution of inline styles and styles from untrusted sources.