CoreServicesUIAgent internals

The recent release of macOS 10.15.2 had some additional updates to the Xprotect yara rules within it. After reviewing what changed in the yara rules I decided to dig a little deeper into how Xprotect gets called. Jonathan Levin’s excellent book MacOS and iOS Internals, Volume III: Security & Insecurity briefly talks about Gatekeeper and Xprotect but didn’t have the internals I was looking for. I ended up finding Patrick Wardle’s excellent presentation from the 2015 Virus Bulletin Conference. His slide deck does a great job of explinaing the communication between LaunchServices, CoreServicesUIAgent and the XprotectService. It did, however, make me question what all does CoreServicesUIAgent do? This posts digs into the internals of CoreServicesUIAgent and documents its functionality.

13 min read

CVE-2019-8805 - A macOS Catalina privilege escalation

With the release of macOS Catalina in October, Apple rolled out a set of interesting new features collectively called System Extensions. System Extensions are a set of user space frameworks encouraging developers who currently maintain and ship kernel extensions to move their features to user space for increased security and stability. One of these new frameworks is the Endpoint Security framework. As a security researcher this framework is of special interest. It’s intended to provide a public and stable API for implementing security products. During the process of looking into what functionality the Endpoint Security framework provided, a privilege escalation bug was identified that would let an attacker execute any code they wanted with root privileges. The following describes both the vulnerability as well as what Apple did to fix the issue.

5 min read

System Extension internals

One of the most exciting things announced at this years WWDC was System Extensions. From a security perspective I think this is a really important advancedment for macOS. It means less third party code running in kernel space which should mean more security and stability. From a programmers perspective I think this is even more important. It means that the code developers previously had to write in C++ can now be written in a more modern language like Swift. Apple has been attempting to wrangle in kexts for a while now and this seems to be the final nail in the coffin. They have said macOS 10.15 will be the last release to fully support kexts without compromises and that in future releases of macOS Kernel Extensions with System Extension equivalents will not load at all. I thought it might be interesting to look at the internals of how System Extensions work.

10 min read

Swift metadata

When reverse engineering macOS binaries that are written in Objective-C, class-dump is a common tool used to extract Objective-C declarations from the runtime information stored in the Mach-O files. With Swift binaries, since there is Objective-C compatability, sometimes you can extract declarations using class-dump but not always. Swift has a rich set of type metadata itself but the documentation is not up to date. With Swift 5 bringing ABI stability I thought it would be interesting to take a look at the type of metadata availble in Swift binaries.

8 min read