Skip to content

Latest commit

 

History

History
98 lines (73 loc) · 7.14 KB

mitigations.md

File metadata and controls

98 lines (73 loc) · 7.14 KB

Mitigation Strategies Analysis for onevcat/kingfisher

Mitigation Strategy: Image Source Validation and Whitelisting (Kingfisher Integration)

Description:

  1. Client-Side Validation: Before passing any URL to Kingfisher methods (e.g., imageView.kf.setImage(with:)), validate the URL against a predefined whitelist of allowed domains and paths. Use a robust URL parsing library (like URLComponents in Swift) to ensure the URL is well-formed and belongs to an allowed domain. Reject any URL that doesn't match.
  2. Avoid String Interpolation: Do not directly construct image URLs by string interpolation with user-provided data. Use URLComponents or similar to build URLs safely.
  3. Custom Resource (Advanced): For more complex validation scenarios, you could create a custom Resource type that encapsulates the URL and performs validation within its initializer. This ensures that only valid resources can be passed to Kingfisher.

Threats Mitigated:

  • Display of Inappropriate Content: (Severity: Medium to High)
  • Image Parsing Exploits (Remote Code Execution): (Severity: Critical)
  • Phishing/Redirection: (Severity: Medium)

Impact:

  • All Threats: Risk significantly reduced by preventing Kingfisher from even attempting to download images from untrusted sources.

Currently Implemented:

  • Basic URL validation (checking for https://) is present in ImageLoader.swift before calling Kingfisher.

Missing Implementation:

  • Full whitelist implementation is missing. The current check is too basic.
  • Custom Resource implementation is not used.

Mitigation Strategy: Cache Poisoning Prevention (Kingfisher Configuration)

Description:

  1. HTTPS Enforcement: Ensure all image URLs passed to Kingfisher use HTTPS. Reject any HTTP URLs before they reach Kingfisher.
  2. Certificate Pinning: Use Kingfisher's built-in support for certificate pinning. This involves providing the expected certificate (or its public key hash) to Kingfisher, typically during the configuration of the KingfisherManager or ImageDownloader. Kingfisher will then reject any connections that don't present the pinned certificate.
  3. Cache Key Review: If you are using custom ImageProcessor or ImageModifier implementations, ensure they are correctly factored into the cache key. Kingfisher's default behavior is usually sufficient, but review your custom code to confirm. Incorrect cache keys could lead to collisions and potential vulnerabilities.
  4. Custom CacheSerializer (Advanced): For extremely high-security scenarios, implement a custom CacheSerializer that performs additional validation on the downloaded image data before it's stored in the cache. This could involve checking a hash of the image against a known-good value.

Threats Mitigated:

  • Cache Poisoning (Man-in-the-Middle): (Severity: High)
  • Cache Poisoning (Server Compromise): (Severity: High)

Impact:

  • Cache Poisoning (Man-in-the-Middle): Risk eliminated with HTTPS.
  • Cache Poisoning (Server Compromise): Risk significantly reduced with certificate pinning; further reduced with a custom CacheSerializer.

Currently Implemented:

  • HTTPS enforcement (as mentioned above).

Missing Implementation:

  • Certificate pinning is not implemented.
  • Cache key review for custom processors is incomplete.
  • Custom CacheSerializer is not implemented.

Mitigation Strategy: Resource Exhaustion (DoS) Prevention (Kingfisher Configuration)

Description:

  1. DownloaderDelegate for Size Limits: Implement the ImageDownloaderDelegate protocol. In the imageDownloader(_:willDownloadImageFor:with:) method, check the response.expectedContentLength. If it exceeds a predefined maximum size (e.g., 10MB), cancel the download using task.cancel().
  2. Timeouts: Configure appropriate timeouts for image downloads using Kingfisher's downloader options (e.g., downloadTimeout on ImageDownloader). This prevents slow or stalled downloads from tying up resources. Use a reasonably short timeout (e.g., 30 seconds).
  3. ImageDownloader Configuration: Use a shared ImageDownloader instance and configure its downloadTimeout and sessionConfiguration properties to control timeouts and other network-related settings. Avoid creating a new ImageDownloader for every request.
  4. KingfisherManager Configuration: If using KingfisherManager, configure its downloader property to use the shared, configured ImageDownloader.

Threats Mitigated:

  • Denial of Service (DoS) - Memory Exhaustion: (Severity: Medium to High)
  • Denial of Service (DoS) - Storage Exhaustion: (Severity: Medium)
  • Denial of Service (DoS) - Network Bandwidth Exhaustion: (Severity: Medium)

Impact:

  • All DoS Threats: Risk significantly reduced.

Currently Implemented:

  • Basic timeouts are configured in Kingfisher's downloader options.

Missing Implementation:

  • DownloaderDelegate implementation for size limits is missing.
  • Review and fine-tuning of timeout values are needed.

Mitigation Strategy: Secure Custom Processors and Modifiers (Kingfisher Usage)

Description:

  1. Code Review: Thoroughly review the code of any custom ImageProcessor or ImageModifier implementations, paying close attention to potential security vulnerabilities (e.g., buffer overflows, integer overflows, injection vulnerabilities).
  2. Input Validation: If your custom processors or modifiers take any input parameters, validate those parameters rigorously to prevent unexpected behavior or exploits.
  3. Unit Testing: Write comprehensive unit tests for your custom processors and modifiers, covering all code paths, edge cases, and error handling.
  4. Cache Key Consideration: Ensure that your custom processor's identifier (and any relevant properties of your custom modifier) are properly incorporated into the cache key. This prevents cache collisions and ensures that processed images are correctly cached.
  5. Avoid External Dependencies: Minimize or avoid using external dependencies within your custom processors. If you must use them, ensure they are well-vetted and secure.

Threats Mitigated:

  • Vulnerabilities in Custom Code: (Severity: Medium to Critical)
  • Logic Errors: (Severity: Low to Medium)
  • Cache Collisions: (Severity: Medium)

Impact:

  • Vulnerabilities in Custom Code: Risk significantly reduced.
  • Logic Errors and Cache Collisions: Risk reduced.

Currently Implemented:

  • Basic unit tests exist for some custom processors.

Missing Implementation:

  • Formal security-focused code review is missing.
  • Input validation is not consistently implemented.
  • Unit test coverage could be improved.
  • Explicit review of cache key generation for custom processors is needed.