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Date: Tue, 24 Mar 2015 16:53:30 +0300
From: Alexander Cherepanov <ch3root@...nwall.com>
To: oss-security@...ts.openwall.com
Subject: Re: CVE for Kali Linux
On 2015-03-24 13:51, Marcus Meissner wrote:
> On Mon, Mar 23, 2015 at 10:41:01PM +0100, Marcus Meissner wrote:
>> On Tue, Mar 24, 2015 at 12:13:06AM +0300, Alexander Cherepanov wrote:
>>> On 2015-03-23 13:38, Marcus Meissner wrote:
>>>>> There are some attacks even if you verify signatures, e.g. serving
>>>>> old, known-vulnerable versions. HTTPS can help here (until
>>>>> signatures start to be widely accompanied by expiring timestamps or
>>>>> something).
>>>>
>>>> SUSE has added an expiry tag in the YUM metadata for such cases.
>>>
>>> It's nice to see progress in this area. Does SUSE guard against
>>> other attacks from [1] too?
>>>
>>> [1] https://isis.poly.edu/~jcappos/papers/cappos_pmsec_tr08-02.pdf
>>
>> Our statements from 2008 (7 years ago) still stand and our package
>> manager does the full repository signing since 2006 already.
>>
>> https://lizards.opensuse.org/2008/07/16/package-management-security-on-opensuse/
Judging only from this text, it seems that one of the crucial points of
your system is "[t]he openSUSE download redirector [that] serves the
metadata from a known and trusted source". And it lives at...
http://download.opensuse.org and is not available over HTTPS at all?
>> "Endless Data Attack" is open, as it is hard to solve for openSUSE with
>> its public mirror system.
If you have signed metadata it should be easy to counter this attack for
packages, right? If you serve you metadata from a trusted source then
it's also solved for metadata. Even if you serve metadata over
non-trusted channel it should be easy to bound the size of "root"
metadata file and record sizes of the next level files in it, etc. Am I
missing any complications?
>> The expiry was something added a bit later after the paper to address
>> the downgrade and replay attacks.
>
> Some more notes.
>
> While the "Update Scenario" is well covered, we are of course facing issues of "bringing up a system".
>
> Like discussed in the thread, how does the customer find a known good ISO image
> for download.
>
> While our installer is protecting itself with GPG signatures, but there is need for
> the root of trust of the CD medium itself.
>
> So for SUSE we publish SHA256 checksums on the https://download.suse.com/ website at least.
> For openSUSE the GPG/SHA and MD5 are on http://software.opensuse.org/132/de .
Hm, it's HTTP and a big part of this thread is about dangers of exactly
this situation.
--
Alexander Cherepanov
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