Exploiting Directory Permissions on MacOS

This talk covers how we can exploit applications on macOS (including macOS itself), where some of the directory / file permissions are incorrectly set. The incorrectness of these settings is not trivial at first sight because understanding these permissions are not intuitive. We will see bugs from simple arbitrary overwrites, to file disclosures and privilege escalation. The concepts applicable to *nix based system as well, however this talk focuses on macOS bugs only. We will also cover different techniques about how to control contents of files, to what we don’t have direct write access.

We will do a deep dive overview of the various r / w / x permissions, what do they mean in case of files, and more importantly in case of directories. We will also take a look at the additional settings, like ownership and the โ€˜lockโ€™ flag and how do they affect the previous permissions. As part of this we will see how to find such bugs.

We will see a file information disclosure bug affecting macOS Mojave, where we can get read access to files which would normally be accessible only for root users. We will also cover 4 vulnerabilities that are caused due to our ability to control the location of certain files. As we have direct control over only the file location, but not the contents, we will explore tricky techniques how we can influence the contents of some of these files to our benefit.

Location: Track 1 Date: April 24, 2020 Time: 11:30 am - 12:30 pm Csaba Fitzl