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 which fixed the fchmod issue > > (commits  and ). > > 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, fixing this last issue (commits  > > and ). > > 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. > > 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
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