Vulnerability Propagation in Package Managers Used in iOS Development

Although using third-party libraries is common practice when writing software, vulnerabilities may be found even in well-known libraries. Detected vulnerabilities are often fixed quickly in the library code. The easiest way to include these fixes in a dependent software application, is to update the used library version. Package managers provide automated solutions for updating library dependencies, which make this process relatively easy. However, library dependencies can have dependencies to other libraries resulting in a dependency network with several levels of indirections. Assessing vulnerability risks induced by dependency networks is a non-trivial task for software developers.The library dependency network in the Swift ecosystem encompasses libraries from CocoaPods, Carthage and Swift Package Manager. These three package managers are used while developing, for example, iOS or Mac OS applications in Swift or Objective-C. We analysed how vulnerabilities propagate in the library dependency network of the Swift ecosystem, how vulnerable dependencies could be fixed via dependency upgrades, and if third party vulnerability analysis could be made more precise given public information on these vulnerabilities.We found that only 5.9% of connected libraries had a direct or transitive dependency to a vulnerable library. Although we found that most libraries with publicly reported vulnerabilities are written in C, the highest impact of publicly reported vulnerabilities originated from libraries written in native iOS languages, i.e., Objective-C and Swift. We found that around 30% of vulnerable dependencies could have been fixed via upgrading the library dependency. In case of critical vulnerabilities and latest library versions, over 70% of vulnerable dependencies would have been fixed via a dependency upgrade. Lastly, we checked whether the analysis of vulnerable dependency use could be refined using publicly available information on the code location (method or class) of a reported vulnerability. We found that such information is not available most of the time.