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macOS Files, Folders, Binaries & Memory

File hierarchy layout

  • /Applications: The installed apps should be here. All the users will be able to access them.
  • /bin: Command line binaries
  • /cores: If exists, it's used to store core dumps
  • /dev: Everything is treated as a file so you may see hardware devices stored here.
  • /etc: Configuration files
  • /Library: A lot of subdirectories and files related to preferences, caches and logs can be found here. A Library folder exists in root and on each user's directory.
  • /private: Undocumented but a lot of the mentioned folders are symbolic links to the private directory.
  • /sbin: Essential system binaries (related to administration)
  • /System: File fo making OS X run. You should find mostly only Apple specific files here (not third party).
  • /tmp: Files are deleted after 3 days (it's a soft link to /private/tmp)
  • /Users: Home directory for users.
  • /usr: Config and system binaries
  • /var: Log files
  • /Volumes: The mounted drives will apear here.
  • /.vol: Running stat a.txt you obtain something like 16777223 7545753 -rw-r--r-- 1 username wheel ... where the first number is the id number of the volume where the file exists and the second one is the inode number. You can access the content of this file through /.vol/ with that information running cat /.vol/16777223/7545753

Applications Folders

  • System applications are located under /System/Applications
  • Installed applications are usually installed in /Applications or in ~/Applications
  • Application data can be found in /Library/Application Support for the applications running as root and ~/Library/Application Support for applications running as the user.
  • Third-party applications daemons that need to run as root as usually located in /Library/PrivilegedHelperTools/
  • Sandboxed apps are mapped into the ~/Library/Containers folder. Each app has a folder named according to the application’s bundle ID (com.apple.Safari).
  • The kernel is located in /System/Library/Kernels/kernel
  • Apple's kernel extensions are located in /System/Library/Extensions
  • Third-party kernel extensions are stored in /Library/Extensions

Files with Sensitive Information

MacOS stores information such as passwords in several places:

Vulnerable pkg installers

OS X Specific Extensions

  • .dmg: Apple Disk Image files are very frequent for installers.
  • .kext: It must follow a specific structure and it's the OS X version of a driver. (it's a bundle)
  • .plist: Also known as property list stores information in XML or binary format.
    • Can be XML or binary. Binary ones can be read with:
      • defaults read config.plist
      • /usr/libexec/PlistBuddy -c print config.plsit
      • plutil -p ~/Library/Preferences/com.apple.screensaver.plist
      • plutil -convert xml1 ~/Library/Preferences/com.apple.screensaver.plist -o -
      • plutil -convert json ~/Library/Preferences/com.apple.screensaver.plist -o -
  • .app: Apple applications that follows directory structure (It's a bundle).
  • .dylib: Dynamic libraries (like Windows DLL files)
  • .pkg: Are the same as xar (eXtensible Archive format). The installer command can be use to install the contents of these files.
  • .DS_Store: This file is on each directory, it saves the attributes and customisations of the directory.
  • .Spotlight-V100: This folder appears on the root directory of every volume on the system.
  • .metadata_never_index: If this file is at the root of a volume Spotlight won't index that volume.
  • .noindex: Files and folder with this extension won't be indexed by Spotlight.

macOS Bundles

Basically, a bundle is a directory structure within the file system. Interestingly, by default this directory looks like a single object in Finder (like .app).

Dyld Shared Cache

On macOS (and iOS) all system shared libraries, like frameworks and dylibs, are combined into a single file, called the dyld shared cache. This improved performance, since code can be loaded faster.
Similar to the dyld shared cache, the kernel and the kernel extensions are also compiled into a kernel cache, which is loaded at boot time.
In order to extract the libraries from the single file dylib shared cache it was possible to use the binary dyld_shared_cache_util which migh not be working nowadays:
dyld_shared_cache_util -extract ~/shared_cache/ /System/Volumes/Preboot/Cryptexes/OS/System/Library/dyld/dyld_shared_cache_arm64e

Special File Permissions

Folder permissions

In a folder, read allows to list it, write allows to delete and write files on it, and execute allows to traverse the directory. So, for example, a user with read permission over a file inside a directory where he doesn't have execute permission won't be able to read the file.

Flag modifiers

There are some flags that could be set in the files that will make file behave differently. You can check the flags of the files inside a directory with ls -lO /path/directory
  • uchg: Known as uchange flag will prevent any action changing or deleting the file. To set it do: chflags uchg file.txt
    • The root user could remove the flag and modify the file
  • restricted: This flag makes the file be protected by SIP (you cannot add this flag to a file).
  • Sticky bit: If a directory with sticky bit, only the directories owner or root can remane or delete files. Typically this is set on the /tmp directory to prevent ordinary users from deleting or moving other users’ files.

File ACLs

File ACLs contain ACE (Access Control Entries) where more granular permissions can be assigned to different users.
It's possible to grant a directory these permissions: list, search, add_file, add_subdirectory, delete_child, delete_child. Ans to a file: read, write, append, execute.
When the file contains ACLs you will find a "+" when listing the permissions like in:
ls -ld Movies
drwx------+ 7 username staff 224 15 Apr 19:42 Movies
You can read the ACLs of the file with:
ls -lde Movies
drwx------+ 7 username staff 224 15 Apr 19:42 Movies
0: group:everyone deny delete
You can find all the files with ACLs with (this is veeery slow):
ls -RAle / 2>/dev/null | grep -E -B1 "\d: "

Resource Forks | macOS ADS

This is a way to obtain Alternate Data Streams in MacOS machines. You can save content inside an extended attribute called com.apple.ResourceFork inside a file by saving it in file/..namedfork/rsrc.
echo "Hello" > a.txt
echo "Hello Mac ADS" > a.txt/..namedfork/rsrc
​
xattr -l a.txt #Read extended attributes
com.apple.ResourceFork: Hello Mac ADS
​
ls -l a.txt #The file length is still q
-rw-r--r--@ 1 username wheel 6 17 Jul 01:15 a.txt
You can find all the files containing this extended attribute with:
find / -type f -exec ls -ld {} \; 2>/dev/null | grep -E "[x\-]@ " | awk '{printf $9; printf "\n"}' | xargs -I {} xattr -lv {} | grep "com.apple.ResourceFork"

Universal binaries & Mach-o Format

Mac OS binaries usually are compiled as universal binaries. A universal binary can support multiple architectures in the same file.

macOS memory dumping

Risk Category Files Mac OS

The files /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources/System contains the risk associated to files depending on the file extension.
The possible categories include the following:
  • LSRiskCategorySafe: Totally safe; Safari will auto-open after download
  • LSRiskCategoryNeutral: No warning, but not auto-opened
  • LSRiskCategoryUnsafeExecutable: Triggers a warning “This file is an application...”
  • LSRiskCategoryMayContainUnsafeExecutable: This is for things like archives that contain an executable. It triggers a warning unless Safari can determine all the contents are safe or neutral.

Log files

  • $HOME/Library/Preferences/com.apple.LaunchServices.QuarantineEventsV2: Contains information about downloaded files, like the URL from where they were downloaded.
  • /var/log/system.log: Main log of OSX systems. com.apple.syslogd.plist is responsible for the execution of syslogging (you can check if it's disabled looking for "com.apple.syslogd" in launchctl list.
  • /private/var/log/asl/*.asl: These are the Apple System Logs which may contain interesting information.
  • $HOME/Library/Preferences/com.apple.recentitems.plist: Stores recently accessed files and applications through "Finder".
  • $HOME/Library/Preferences/com.apple.loginitems.plsit: Stores items to launch upon system startup
  • $HOME/Library/Logs/DiskUtility.log: Log file for thee DiskUtility App (info about drives, including USBs)
  • /Library/Preferences/SystemConfiguration/com.apple.airport.preferences.plist: Data about wireless access points.
  • /private/var/db/launchd.db/com.apple.launchd/overrides.plist: List of daemons deactivated.