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Date: Mon, 24 Sep 2012 11:21:54 -0600
From: Kurt Seifried <kseifried@...hat.com>
To: oss-security@...ts.openwall.com
CC: Tavis Ormandy <taviso@...xchg8b.com>
Subject: Re: Re: Re: CVE request(?): gpg: improper file permssions
set when en/de-crypting files
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On 09/24/2012 11:15 AM, Kurt Seifried wrote:
> On 09/24/2012 02:42 AM, Tavis Ormandy wrote:
>> Matthias Weckbecker <mweckbecker@...e.de> wrote:
>
>>> On Friday 21 September 2012 23:47:48 Michael Gilbert wrote:
>>> [...]
>>>>
>>>> So anyway, I suppose this creates more questions than
>>>> answers, but I guess its worth thinking about. After all,
>>>> what did the user really expect? If they had intended that
>>>> original file to be private, and now its not, is that
>>>> appropriate? Is it more appropriate to assume all users know
>>>> how to use umask appropriately?
>>>>
>>>
>>> IMO if one bothers to encrypt a file at all it was certainly
>>> intended to be private and only supposed to be readable by a
>>> certain user / user group and not by just everyone. Otherwise
>>> encryption would be pointless, or are there any other reasons
>>> for encrypting a file?
>>>
>>>> Best wishes, Mike
>>>
>>> Thanks, Matthias
>>>
>
>> I agree. Users do know how to use umask properly, but this isn't
>> what umask is for. The umask for the low order bits are only
>> applied if the program requested 0666, it's still the
>> responsibility of the program to choose the appropriate
>> permissions.
>
>> Creating sensitive files with 0666 and then saying "set your
>> umask" is just wrong.
>
>> Tavis.
>
> So where do we draw the line? tar? By this definition any program
> that has stores sensitive data (passwords/etc.) or has potentially
> sensitive output (so email, web clients, chat clients, file
> downloaders, text editors, etc.) needs to internally pick some
> "safe" default and apply it and/or umask (whichever is more secure
> I guess).
>
> Personally I think applying file permissions at the program level
> is in general (outside of some highly specific instances like
> encryption key generation and storage in a file) a very very bad
> place to do this. Moving it up a layer to the OS (e.g. umask, home
> dir permissions, etc.) makes way more sense I think.
>
> However if people want to go ahead with this then a short list
> would be:
>
> OpenSSH/any SSH or encrypted connection client OpenSSL/anything
> that generates certificates/keys/etc. GPG/PGP/anything that
> provides file encryption/decryption Email clients (email is almost
> always sensitive, stored passwords/certs) Web clients (cached web
> pages are sensitive, stored passwords/certs) Chat programs (IRC,
> MSN, etc.) (stored passwords/certs) Any programs storing
> financial/accounting data (GnuCash, etc.). Any programs storing
> health related data (GnuHealth, etc.). File editing programs were
> previously mentioned
>
> I'm sure I've missed a few.
Sorry I forgot to include this:
Also trying to fix this in a lot of programs has a major downside:
systems with bad umasks/home directory permissions/etc. remain hidden
to the user potentially. E.g. if programs start policing its file
output permissions this works great until the user uses a program that
doesn't do this (which they will do, probably sooner than later).
Now that's not to say that some specific instances of data that by
definition MUST be secret (e.g. secret passwords, certificate keys,
etc.) should have their permissions policed by their respective
program (due to the fact that they are quite often used on shared
systems/etc.), but this is a vastly smaller set of programs and much
more manageable.
- --
Kurt Seifried Red Hat Security Response Team (SRT)
PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993
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