Date: Wed, 15 Jun 2011 10:11:55 +0200 From: Bernhard Reiter <bernhard@...evation.de> To: Josh Bressers <bressers@...hat.com> Cc: oss-security@...ts.openwall.com, Tomas Mraz <tmraz@...hat.com>, "Steven M. Christey" <coley@...us.mitre.org>, Werner Koch <wk@...code.com> Subject: Re: CVE Request / Discussion -- dirmngr -- Improper dealing with blocking system calls, when verifying a certificate 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 , 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: > >  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 -- Managing Director - Owner: www.Intevation.net (Free Software Company) FSFE.org: Founding GA Member. Kolabsys.com: Board Member Intevation GmbH, Osnabrück, DE; Amtsgericht Osnabrück, HRB 18998 Geschäftsführer Frank Koormann, Bernhard Reiter, Dr. Jan-Oliver Wagner Download attachment "smime.p7s" of type "application/pkcs7-signature" (3696 bytes)
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