Openwall GNU/*/Linux - a small security-enhanced Linux distro for servers
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 11 Jul 2012 10:48:48 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: Dustin Kirkland <dustin.kirkland@...zang.com>
CC: Tyler Hicks <tyhicks@...onical.com>, oss-security@...ts.openwall.com,
        Marcus Meissner <meissner@...e.de>,
        Dan Rosenberg <dan.j.rosenberg@...il.com>
Subject: Re: ecryptfs headsup

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 07/11/2012 08:08 AM, Dustin Kirkland wrote:
> On Tue, Jul 10, 2012 at 5:15 PM, Tyler Hicks
> <tyhicks@...onical.com> wrote:
>> On 2012-07-10 15:13:40, Tyler Hicks wrote:
>>> On 2012-07-10 16:48:26, Dan Rosenberg wrote:
>>>> On 07/10/2012 10:30 AM, Marcus Meissner wrote:
>>>>> On Tue, Jul 10, 2012 at 04:21:13PM +0200, Sebastian Krahmer
>>>>> wrote:
>>>>>> 
>>>>>> It is a potential privilege escalation since the pam
>>>>>> module was not setting uid/gid(list) appropriately and
>>>>>> the suid binary did not clear environment before exec'ing
>>>>>> umount. I do not know whether MS_NOSUID was really needed
>>>>>> (and maybe MS_NODEV is, but I was not able to create dev
>>>>>> files). Unfortunally we found ecryptfs not really stable
>>>>>> inside the kernel and Marcus is still rebooting :)
>>>>> 
>>>>> This means ...
>>>>> 
>>>>> So far we have not yet found a specific security issue.
>>>>> 
>>>>> Ciao, Marcus
>>>>> 
>>>> 
>>>> This reminds me...
>>>> 
>>>> If an unprivileged user can mount ecryptfs shares (e.g. via
>>>> the setuid-root mount helper shipped on Ubuntu) and has the
>>>> ability to mount user-controlled filesystems (either network
>>>> filesystems via setuid mount helpers like mount.cifs or
>>>> mount.nfs, or formatted USB drives via physical access), it's
>>>> possible to escalate privileges to root because the setuid
>>>> ecryptfs helper does not mount filesystems with the nosuid or
>>>> nodev flags.
>>>> 
>>>> An attacker can create an ecryptfs filesystem on his own
>>>> machine on a network filesystem or USB drive, and then mount
>>>> that ecryptfs filesystem on the victim machine for a
>>>> setuid-root backdoor.  Hard-coding nosuid and nodev into the 
>>>> setuid ecryptfs helper would resolve this, but I'm not sure
>>>> that's workable for Ubuntu home directories.
>>> 
>>> This vulnerability is limited to physical access via formatted
>>> USB drives because the eCryptfs filesystem code does not work
>>> on top of network filesystems.
>>> 
>>> Additionally, I believe that the encrypted home source and
>>> destination mount points were hard-coded up until
>>> ecryptfs-utils version 86. Versions before that should not be
>>> vulnerable to the setuid-root binary on a USB drive attack
>>> mentioned above.
>>> 
>>> Dustin - Would you have any objections to forcing the nosuid
>>> and nodev mount options in the mount.ecryptfs_private helper?
> 
> Hi Tyler, et al.-
> 
> I don't have any objections at all with adding nosuid and nodev to
> the hardcoded mount.ecryptfs_private options.
> 
> Actually, I seem to recall this coming up recently before.  I
> can't find the bug or email thread (must have been IRC), but I
> recall offering to commit, test, and release that change
> immediately.  I believe I was asked to wait to do that until a CVE
> had been published...  I can't find any record of that conversation
> though, so that's just from memory.
> 
> Shall I go ahead and commit/test/release that now, Tyler?

So it sounds like a non privileged user on an Ubuntu machine can
insert a USB stick/etc with a file system that gets automatically
mounted, said file system can contain setuid root binaries for example
which the user can then execute, elevating privileges?

- -- 
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993



-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.12 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/
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=N1iI
-----END PGP SIGNATURE-----

Powered by blists - more mailing lists

Your e-mail address:

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.