[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <201209071126.35198.geissert@debian.org>
Date: Fri, 7 Sep 2012 11:26:34 -0500
From: Raphael Geissert <geissert@...ian.org>
To: Tomas Hoger <thoger@...hat.com>
Cc: oss-security@...ts.openwall.com
Subject: Re: CVE request: opencryptoki insecure lock files handling
Hi,
On Friday 07 September 2012 06:32:39 Tomas Hoger wrote:
> On Thu, 6 Sep 2012 20:03:20 -0500 Raphael Geissert wrote:
> > It is possible for an attacker to replace the lock files with
> > symlinks and have pkcsslotd (or others) fchmod the target of the
> > symlink to make it world-writable, create arbitrary files, etc.
>
> There were following problems that I'm aware of:
>
> - /tmp/.pkapi_xpk - This was normally created by pcksslotd (running as
> root). Symlink attack on this did not allow corrupting / truncating
> files, but allowed creating new empty files at arbitrary locations.
>
> - /tmp/.pkcs11spinloc - I believe this is created by opencryptoki
> clients. In addition to the above, there's a chmod to make this file
> world writable. This may get created by non-root user, but chmod
> may still run later with root privileges later.
>
> Those files do not seem to get removed as part of the normal operation,
> so replacing them with symlinks if they already exist is limited
> by /tmp stickiness. Attacker does not need to be pkcs11 group member.
Correct, and to make it clear: /tmp/.pkcs11spinloc *is* chmod'ed by
pcksslotd to make it world-writable.
> > In response, upstream released 2.4.1[1] which fixed the fchmod issue
> > (commits [3] and [4]).
>
> 2.4.1 moved those files that became /var/lock/LCK..opencryptoki
> and /var/lock/LCK..opencryptoki_stdll respectively.
>
> > Niels discovered that 2.4.1 still allowed arbitrary files creation by
> > following symlinks.
>
> Would you mind clarifying? As files were moved to /var/lock, this
> should require attacker to have permissions to write to that directory.
At least in Debian (and its derivatives):
$ stat -c %a /var/lock/
1777
> > Upstream then released 2.4.2[2], fixing this last issue (commits [5]
> > and [6]).
>
> What do 2.4.2 actually fix? I think the move of /tmp/.pkcs11spinloc
> to /var/lock/LCK..opencryptoki_stdll probably created a regression in
> use cases where opencryptoki clients run without root privileges (or
> better to say without privileges to create the file in /var/lock/).
Given the above (/var/lock/ is world-writable), 2.4.1 doesn't cause a
regression for non-root users.
The move to the subdirectory in /var/lock limits the attack surface to
members of the pkcs11 group, who are fully trusted, therefore becoming a
non-issue.
> Another move to pkcs11 group writable /var/lock/opencryptoki seems to
> resolve that, but it also negates benefits of the 2.4.1 security fix.
> Based on the rather quick look at the patches you pointed out, 2.4.2
> seems to have the same problems pre-2.4.1 had, with following changed
> conditions:
> - attacker now needs to be pkcs11 group member
> - lack of directory stickiness should make it easier to execute the
> attack
>
> > Even with the fixes in 2.4.2, members of the pkcs11 group could still
> > use symlink attacks. However, as per upstream's documentation,
> > members of such group are expected to be trusted[7].
>
> Correct, any pkcs11 group member can easily compromise any other user
> using opencryptoki library see:
> https://bugzilla.redhat.com/show_bug.cgi?id=730635
>
> Upstream does not see that as an issue though...
Yeah, I saw it...
Cheers,
--
Raphael Geissert - Debian Developer
www.debian.org - get.debian.net
Powered by blists - more mailing lists
Please check out the
Open Source Software Security Wiki, which is counterpart to this
mailing list.
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
