/clbx

CLBX file format

CLBX Specification

CLBX is an extraction container format from Cellebrite, supporting modern mobile filesystem acquisitions. This light-weight format is designed for simplicity, interoperability, and storing complete forensic metadata for each file.

This document describes version 0.3.0 of the format. This first release specifically addresses iOS extractions, but Android and other OS can and will be supported in future releases.

Format

The following directory structure is stored inside a ZIP archive:

filesystem{suffix}/   # extracted files go here
metadata{suffix}/     # metadata goes here
  metadata.msgpack    #   metadata per file 
  filesystem.msgpack  #   filesystem-wide metadata
extra/                # vendor-specific auxiliary files
version               # text file containing "CLBX-{semver}"

Each CLBX archive can hold multiple distinct filesystems (e.g. both System and Data partitions of an iOS device). Each will create a pair of filesystem and metadata directories with the same {suffix}. {suffix} has no intrinsic meaning and can be either a descriptive string or a random token. An empty {suffix} is also valid.

filesystem directories contain a copy of the extracted file tree, as well as partial metadata fields as natively supported by the ZIP specification. metadata directories contain additional metadata, listing every file and all extracted fields.

filesystem/

Files are stored uncompressed to make parsing and referencing specific artifacts inside the archive easier.

The following ZIP metadata fields are populated for convenience, to allow easier manual inspection of the extracted contents without requiring any proprietary tools:

  • Mode - Filetype and UNIX permissions are stored in the External Attributes field of each file.
  • Timestamps - Modification, Access, and Creation (birth) time are stored in 1-second resolution in a Timestamps Extra Field (0x5455).
  • GID/UID - Stored in a 0x7875 New Unix Extra Field.
  • Symbolic links are stored as per Info-ZIP extensions.
  • Special files (such as special char/block devices, sockets, etc. but not including symlinks) are stored as empty files in the zip with proper mode and metadata set.

metadata.msgpack

The complete and authoritative source of metadata is stored in a MessagePack encoded dictionary mapping between paths and metadata objects. Each metadata object is a dictionary mapping between text representations of fields.

Importantly, metadata.msgpack may include references to files whose contents are inaccessible or could not be extracted for any reason. This metadata may provide special value for partial extractions (BFU, AFU) where file content is inaccessible but file metadata is available for forensic analysis.

field description example value
mode as returned from stat() 16877
uid as returned from stat() 33
gid as returned from stat() 33
size as returned from stat() 2016
inode as returned from stat() 36516
mtime as returned from stat() 1583760561632663172
ctime as returned from stat() 1583760562436419507
atime as returned from stat()
btime as returned from stat() 1570675980000000000
links as returned from stat() 63
prot enum value of Protection Class (iOS only) 0
xattr key-value dictionary of Extended Attributes {'com.apple.installd.installType': b'\x00\x00\x00\x00\x00\x00\x00\x00', 'com.apple.installd.uniqueInstallID': b'c63ad8cedd13171ad9832bbd653e2a9e'

Timestamps are stored with nano-second precision.

Example:

{
 'Applications/Apple TV Remote.app/PlugIns/TVRemoteIntentExtension.appex/zh_TW.lproj/Intents.strings': {'atime': 1570672647000000000,
  'uid': 0,
  'btime': 1570672647000000000,
  'size': 1945,
  'gid': 80,
  'inode': 9084,
  'ctime': 1570672647000000000,
  'links': 1,
  'mtime': 1570672647000000000,
  'mode': 33204,
  'prot': 0,
  'xattr': {}},
 'Applications/AskPermissionUI.app/Info.plist': {'atime': 1570672625000000000,
  'uid': 0,
  'btime': 1570672625000000000,
  'size': 1240,
  'gid': 80,
  'inode': 5022,
  'ctime': 1570672625000000000,
  'links': 1,
  'mtime': 1570672625000000000,
  'mode': 33204,
  'prot': 0,
  'xattr': {}},
 'Applications/AppStore.app/PlugIns/SubscribePageExtension.appex/zh_HK.lproj': {'atime': 1570672632000000000,
  'uid': 0,
  'btime': 1570672632000000000,
  'size': 96,
  'gid': 80,
  'inode': 6942,
  'ctime': 1570672635000000000,
  'links': 3,
  'mtime': 1570672632000000000,
  'mode': 16893,
  'prot': 0,
  'xattr': {}},
 'private/var/containers/Bundle/Application/8F1372CA-A085-400E-A163-76059AB7B941/MobileCal.app': {'atime': 1570676008000000000,
  'uid': 33,
  'btime': 1570675980000000000,
  'size': 2016,
  'gid': 33,
  'inode': 36516,
  'ctime': 1583760562436419507,
  'links': 63,
  'mtime': 1583760561632663172,
  'mode': 16877,
  'prot': 0,
  'xattr': {'com.apple.installd.installType': b'\x00\x00\x00\x00\x00\x00\x00\x00',
   'com.apple.installd.uniqueInstallID': b'c63ad8cedd13171ad9832bbd653e2a9e'}},
 ...}

Notes

When parsing the container for forensic purposes, you should rely on the authoritative metadata copy as referenced in metadata.msgpack.

In cases of a live system acquisition, files and file metadata may change from the moment of metadata collection to the moment of file collection itself.

filesystem.msgpack

The file contains a MessagePack encoded dictionary mapping between string encoded key-value pairs describing the corresponding filesystem.

Keys:

  • "mount_point": The logical path a given filesystem should exist. If missing, it should be treated as if mount_point is /.

Examples:

{"mount_point": "/"}

(suitable for iOS System partition)

{"mount_point": "/private/var"}

(suitable for iOS Data partition)

extra/

Holds vendor-specific auxiliary files for the extraction (e.g. ufd file, keychain/keystore records)

version

Contains the magic CLBX- followed by a SemVer version for the format. For example: CLBX-0.3.0.

Copyright (C) 2021 Cellebrite DI LTD