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attack-surface.md

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Attack Surface Analysis for onevcat/kingfisher

Attack Surface: 1. Remote Image Source Manipulation

  • Description: Attackers control the URLs passed to Kingfisher, leading to malicious image downloads.
  • Kingfisher Contribution: Kingfisher is the component that fetches and displays images from the provided URLs, making it the direct target of this manipulation. It executes the request based on the attacker-controlled input.
  • Example: An attacker injects a URL pointing to a crafted image designed to exploit a vulnerability in the system's image decoding library (e.g., a buffer overflow, even if that library isn't part of Kingfisher). Or, the URL points to a massive image to cause a DoS.
  • Impact:
    • Remote Code Execution (RCE) if a vulnerability in image processing (even external to Kingfisher) is exploited.
    • Denial of Service (DoS) due to resource exhaustion (Kingfisher downloads the large file).
    • Information Disclosure (e.g., through SSRF, though this is more indirect).
  • Risk Severity: Critical (if RCE is possible) or High (for DoS and information disclosure).
  • Mitigation Strategies:
    • Strict URL Whitelisting: Only allow image loading from a predefined list of trusted domains. Reject any URL not on the whitelist. This is the most important mitigation.
    • Input Validation and Sanitization: Thoroughly validate and sanitize any user input or data from external sources that contribute to the image URL.
    • Content Security Policy (CSP): Implement a strong CSP to restrict the domains from which images can be loaded. This is crucial defense-in-depth.
    • Download Size and Timeout Limits: Configure Kingfisher's maxContentLength and downloadTimeout to prevent excessive resource consumption. This directly mitigates the DoS aspect.
    • Server-Side URL Validation (if applicable): If URLs are generated server-side, ensure that process is secure against SSRF and other injection attacks.

Attack Surface: 2. Cache Poisoning

  • Description: Attackers modify Kingfisher's image cache to replace legitimate images with malicious ones.
  • Kingfisher Contribution: Kingfisher's caching mechanism is the direct target. If the cache is compromised, Kingfisher will serve the malicious image.
  • Example: An attacker gains access to the device's file system (e.g., through a separate vulnerability) and replaces a cached image file with a malicious one. Subsequent requests for that image will be served by Kingfisher from the poisoned cache.
  • Impact:
    • Display of malicious or inappropriate content.
    • Potential for exploiting vulnerabilities in downstream image processing if the application further processes cached images (even if that processing is outside of Kingfisher).
  • Risk Severity: High.
  • Mitigation Strategies:
    • Secure Cache Storage: Rely on the operating system's security mechanisms to protect the cache directory. This is a platform-level concern, but Kingfisher's use of the cache is the direct vulnerability.
    • Strong Cache Keys: Kingfisher uses the URL as the default cache key. Therefore, robust URL validation (as described in #1) is absolutely essential to prevent predictable cache keys, and thus, is a direct Kingfisher-related mitigation.
    • Cache Expiration: Use appropriate cache expiration policies (e.g., diskCache.expiration) to limit the lifetime of cached images, reducing the window of opportunity. This is a direct Kingfisher configuration setting.
    • Cache Integrity Checks (Advanced): Consider checksums (more complex, but directly related to how Kingfisher could be modified to be more secure).

Attack Surface: 3. Malicious Image Processor Exploitation

  • Description: If a custom ImageProcessor is used, vulnerabilities within that processor could be exploited by a crafted image.
  • Kingfisher Contribution: Kingfisher provides the framework for applying image processors and calls the custom processor. The vulnerability is in the custom code, but Kingfisher is the mechanism that delivers the malicious input to that code.
  • Example: A custom ImageProcessor uses a vulnerable third-party library. An attacker provides an image to trigger a buffer overflow in that library through Kingfisher's processing pipeline.
  • Impact:
    • Potentially Remote Code Execution (RCE) if the vulnerability in the custom processor allows it.
    • Application crashes or instability.
  • Risk Severity: High (potentially Critical if RCE is possible).
  • Mitigation Strategies:
    • Thorough Code Audit: Rigorously audit any custom ImageProcessor implementations. This is crucial because Kingfisher directly uses this code.
    • Secure Coding Practices: Follow secure coding practices when developing custom processors.
    • Dependency Management: Keep any third-party libraries used by the custom processor up-to-date (relevant because Kingfisher uses the processor).
    • Input Validation (within Processor): Even within the custom processor, validate the image data before processing. This is a direct mitigation for code called by Kingfisher.