threat-modeling.md

Threat Model Analysis for mwaterfall/mwphotobrowser

Threat: Uncontrolled Image Decoding Leading to Denial of Service

• Description: An attacker crafts a malicious image file (e.g., extremely large dimensions, compressed in a way that expands massively upon decompression, or using a known vulnerability in an image decoding library that MWPhotoBrowser uses internally) and provides it to the application. When MWPhotoBrowser attempts to decode this image internally, it consumes excessive memory or CPU, leading to a crash or unresponsiveness. This is distinct from the application simply passing a large image; this focuses on vulnerabilities within MWPhotoBrowser's decoding process.
• Impact: Application crash, denial of service for the user. Potentially, the entire device could become unresponsive if memory exhaustion is severe enough.
• Affected Component: The image decoding logic within MWPhotoBrowser. This likely relies on underlying iOS frameworks like UIImage and related image I/O functions (e.g., imageWithContentsOfFile:, imageWithData:). However, if MWPhotoBrowser has custom decoding logic for specific image formats or optimizations, that custom code is the primary concern. The methods used for displaying images (e.g., within MWZoomingScrollView or related view controllers) are also relevant, as they trigger the decoding.
• Risk Severity: High
• Mitigation Strategies:
  • Review MWPhotoBrowser's Code: Thoroughly review the image loading and decoding code within MWPhotoBrowser itself. Look for any custom decoding logic or areas where large images might not be handled gracefully.
  • Memory Management Audit: Audit the memory management within MWPhotoBrowser's image handling. Ensure resources are released promptly. Use Instruments to profile memory usage during image loading.
  • Fuzz Testing (Targeted): Perform fuzz testing specifically targeting MWPhotoBrowser's image loading and display components. Provide a wide range of valid and invalid/malformed image inputs directly to the library's functions (bypassing any application-level validation, to test the library's robustness in isolation).
  • Dependency Analysis (Image Libraries): If MWPhotoBrowser uses any external libraries for image decoding (check its dependencies), analyze those libraries for known vulnerabilities. Update them if necessary.
  • Limit Image size and dimensions (within MWPhotoBrowser): If possible, modify MWPhotoBrowser's code to enforce limits on image size and dimensions before attempting to decode. This is a defense-in-depth measure.

Threat: Caching of Sensitive Images After Logout (If MWPhotoBrowser has its own caching)

• Description: A user views sensitive images. MWPhotoBrowser's internal caching mechanism (if it has one, independent of NSURLCache or SDWebImage) stores these images. After logout, these cached images remain accessible, potentially to an attacker with device access. This threat only applies if MWPhotoBrowser has its own, custom caching implementation.
• Impact: Unauthorized access to sensitive image data after the user has logged out. Breach of confidentiality.
• Affected Component: Any custom caching mechanism implemented within MWPhotoBrowser. This would likely involve storing image data in files or in-memory data structures. Examine the source code for any such mechanisms. If it only relies on NSURLCache or SDWebImage, this threat is mitigated by clearing those caches (which is the application's responsibility).
• Risk Severity: High (if the images are sensitive and a custom cache exists)
• Mitigation Strategies:
  • Code Review (Caching): Thoroughly review MWPhotoBrowser's source code to determine if it implements any custom caching. If so, analyze how this caching works and where the cached data is stored.
  • Cache Clearing (Internal): If a custom cache exists, modify MWPhotoBrowser to provide a method for explicitly clearing this cache. The application should call this method on logout.
  • Ephemeral Storage (Internal): If feasible, modify MWPhotoBrowser's custom caching (if it exists) to use ephemeral storage that is automatically cleared by the operating system.
  • Document Caching Behavior: Clearly document MWPhotoBrowser's caching behavior (or lack thereof) in its documentation, so developers are aware of their responsibilities.

Threat: Dependency Vulnerabilities (Directly affecting MWPhotoBrowser)

• Description: MWPhotoBrowser itself depends on other libraries. If these dependencies have known, high or critical vulnerabilities that can be exploited through MWPhotoBrowser's functionality, an attacker could compromise the application. This focuses on vulnerabilities in libraries that MWPhotoBrowser directly uses and that impact its core image handling or display.
• Impact: Varies depending on the specific vulnerability, but could include denial of service, arbitrary code execution (less likely, but possible), or information disclosure.
• Affected Component: Any part of MWPhotoBrowser that utilizes a vulnerable dependency. The vulnerability might be triggered through image loading, display, or other library features.
• Risk Severity: High (depending on the dependency vulnerability)
• Mitigation Strategies:
  • Dependency Analysis (Focused): Specifically analyze the dependencies directly used by MWPhotoBrowser. Identify any libraries involved in image handling, networking, or other core functions.
  • Vulnerability Scanning (Dependencies): Use vulnerability scanning tools to check for known vulnerabilities in MWPhotoBrowser's direct dependencies.
  • Update Dependencies (MWPhotoBrowser): Keep MWPhotoBrowser's dependencies up-to-date. If MWPhotoBrowser itself is not actively maintained, consider forking it to update its dependencies.
  • Alternative Libraries (If Necessary): If a critical dependency is consistently vulnerable and cannot be updated, consider modifying MWPhotoBrowser to use an alternative library or removing the dependency if it's not essential.