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Date: Thu, 17 Nov 2016 19:54:20 -0500
From: Jacobo Avariento <spinfoo.vuln@...il.com>
To: oss-security@...ts.openwall.com
Cc: john.haxby@...cle.com, osssecurity@...edaemon.net
Subject: Re: CVE-2016-4484: - Cryptsetup Initrd root Shell

Good debate.

Actually when using full disk encryption, to lock the BIOS and GRUB must
be mandatory, otherwise you are protecting your confidentiality but not
your integrity. Even with a password in GRUB with an unprotected BIOS
you can also boot from a USB device and access encrypted partitions,
delete them, etc.

Just to mention another method complimentary to the "rd.shell=0" a
similar behaviour to this "flaw" can be achieved using at the boot
sequence "rd.break=pre-udev", this also gives you a root shell with
access to the hard disk.

Regards


On 11/17/2016 02:15 PM, John Haxby wrote:
> On 17/11/16 17:50, Jason Cooper wrote:
>> Hi John,
>>
>> On Thu, Nov 17, 2016 at 04:56:06PM +0000, John Haxby wrote:
>>>> On 17/11/16 16:39, Jason Cooper wrote:
>>>>>> However, the golden rule still applies.  Physical access trumps all
>>>>>> defensive measures.  The absolute best you can do is detect that
>>>>>> physical access occurred.  From there, you're hoping there are no
>>>>>> hardware implants or other devices outside the scope of software
>>>>>> security.
>>>> I agree.  However, it ought be to be harder than leaning on the enter
>>>> key to break into a system.  You lock your doors even though it doesn't
>>>> stop a determined burglar?
>> Yes, as I said before, non-deterministic failure modes are bad.  This
>> CVE is a bug in the initrd script and needs to be fixed.  What I
>> disagree with, and still do, is the "sky is falling!" nature of the
>> alert.
> Yup.  I agree there, but that's down to the publicity its received.  We
> can't do much but grin and bear that.   Red Hat have given this a CVSS2
> score of 7.2 which reflects the _potential_ severity but marked it as
> "moderate" which reflects the actual effect.   It's most serious for
> people like me who have an encrypted root but no grub password (and no
> rd.shell=0) but, no, the sky is not falling.
>
> jch
>

-- 
https://github.com/spinfoo
https://pa.linkedin.com/in/jacoboavariento

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