Re: CVE Request / Discussion -- dirmngr -- Improper dealing with blocking system calls, when verifying a certificate

[Josh Bressers <bressers () redhat com>]

Please use CVE-2011-2207.

Thanks.

-- 
    JB


----- Original Message -----
> Dear Jan, Gentlemen,
>
> thanks for caring about the issue, here is my input:
>
> Am Montag, 6. Juni 2011 19:42:10 schrieb Josh Bressers:
> > > IOW was not able to reproduce the complete / indefinite
> > > dirmngr-client
> > > hang (thus blocking other clients from access). As noted in [6],
> > > it is
> > > true that during small time period running 'dirmngr' daemon
> > > instance is
> > > unresponsive also for '--ping' (dirmngr-client --ping) commands,
> > > but
> > > after finite time (~21 seconds in my test) the connection ends up
> > > with
> > > timeout.
> > >
> > > Though Bernard in:
> > > [7] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=627377#5
> > >
> > > mentions "For example the KMail hung when trying to verify a
> > > signature
> > > which has the certificate in the chain." which would suggest there
> > > may
> > > exist clients / end-user application not able to recover from this
> > > bug
> > > properly. Bernhard, hopefully here, you could clarify / list such
> > > applications and provide also time details, how long that hang of
> > > such
> > > applications took.
>
> For me the verification of the certiciate DTAG_Issuing_CA_i01.der
> hangs for several minutes, e.g. just tested on Debian Lenny
> for three minutes:
> real 3m9.237s
> user 0m0.000s
> sys 0m0.004s
> The time might depend on some network parameters or network timeouts
> of the operating system. I have not changed these on my test system,
> but I am also not very knowledgable about the various timeouts.
>
> Three minutes are way too much. People that use Kontact will
> experience a
> freeze of the application for that time and must assume their client
> application to be hung or crashed. Given that Kontact is also a
> calender
> and contacts manager, this causes significant interruptions in a
> typical
> office.
>
> Applications affected are all applications that use dirmngr in a
> blocking
> way. Applications use dirmngr when they are trying to use the GnuPG
> crypto
> stack with CMS operations (aka X509 certificated, e.g. used with
> S/MIME
> emails or similar file crypto operations) and use of dirmngr is not
> explicitely switched off. The default is to use dirmngr for
> certification
> revocation on all CMS operations that involve certificates.
>
> The application I have tested is KMail/Kontact which uses GnuPG via
> the
> library gpgme, which is the recommended way. Command line usage of
> gpgsm is
> also affected, which I have also verified.
>
> > > Based on your reply, this may not / may be worthy (in case there
> > > are
> > > such end-user applications) of an CVE identifier.
> >
> > Is this expected to only be used by end user applications?
>
> Gpgsm or gpgme can be used by system scripts, other scripts or system
> applications as well. Dirmngr itself is a system service, so on a
> multiuser
> system all users are affected once one user tries a verification
> waiting
> for a network timeout.
>
> > It seems to me
> > that if an attacker can DoS a client, it's not a security issue,
> > especially
> > when you consider the use (if a bad guy can interact with dirmngr,
> > there
> > are probably bigger potential issues).
>
> Two attack scenarios:
> a) a local uses wants to block other users from using email or crypto
> operations, like encrypting or verifying signatures to someone. This
> user can
> just initiate this verification with the system dirmngr. Any user of a
> system
> should be able to ask the system dirmngr for verifications. So all
> users have
> access.
>
> b) A remote user wants to cause interruptions and sends signed emails
> or files
> that causes an gpgsm to attempt to decrypt or verify with such a
> certificate.
> This will often be done automatically by the email clients for the
> comfort of
> the user. As gpgsm and thus dirmngr is needed to decide if a signature
> is
> good, attackers can assume that emails with such a signature will be
> passed
> to gpgsm who will pass the certificate to dirmngr and ask for
> verification.
> So it is a normal situation that outside data will reach dirmngr.
>
> Best Regards,
> Bernhard Reiter
>
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