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Re: Mac OS X stores login/Keychain/FileVault passwords on disk
Jul 16 2004 02:51PM
johnny ihackstuff com
The issue of getting into AES128 encrypted disk images is easy to
unravel with this swapfile problem.
We'll start by grabbing the volume name of an AES128 encrypted disk
image file. Assuming the image name is test1.dmg, try:
root# strings -8 /var/vm/swapfile* | grep -B1 test1.dmg | grep
Armed with the volume name, we can grab the file listing of that
(supposedly protected) AES128 encrypted disk image. Since our
volume name is 'SECRET'. Try:
root# strings -8 /var/vm/swapfile* | grep "<string>/Volumes/SECRET"
To REALLY get at those (supposedly protected) files, we could use the
password. It's easy to grab it even if it's not in the keychain:
root# strings -8 /var/vm/swapfile* | grep -B1 "/System/Library/
[... snip ... ]
[... snip ... ]
The only chore may be figuring out which password goes with which
disk image. And that's not nearly the chore of popping AES128
johnny (at) ihackstuff (dot) com [email concealed]
From: Adi Kriegisch <adi (at) cg.tuwien.ac (dot) at [email concealed]>
To: bugtraq (at) securityfocus (dot) com [email concealed]
Subject: Re: Mac OS X stores login/Keychain/FileVault passwords on
Sent: Monday, July 12, 2004 9:05 AM
The swapfiles are deleted on startup -- this means even a clean
user leaves the passwords on disk.
So if you loose your powerbook someone might boot it in "target disk
will be able to get your password!
It seems that Mac OS X (10.3.4 tested) doesn't bother clearing memory
containing sensitive data, or using mlock() to avoid swapping.
A quick grep of the swapfiles will show up various morsels:
rez:~> sudo strings -8 /var/vm/swapfile0 |grep -A 4 -i longname
<user's password here>
... various other occurrences follow
Grepping for context around "password" also shows up results, and
for portions of a Keychain password (differing from the login password)
will also get results. It appears that loginwindow is one of the apps
involved, I haven't investigated what else is involved. The amount of
memory and usage patterns of the machine will affect what gets
though loginwindow seems likely to get swapped early since it is
used after login.
Obviously this is only of interest if an attacker has root (or physical)
access to a machine, however it does make FileVault or Keychain
fairly useless. It appears that the swapfiles are removed on shutdown
startup, though not wiped - pulling the power from a sleeping
and/or booting from CD, would quite easily retrieve the password(s).
Reported to Apple on 21 June, I haven't had any response. It'd be nice
they at least said "we're taking a look if it's an issue".
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