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Message-ID: <20141215141342.GB5363@suse.de>
Date: Mon, 15 Dec 2014 15:13:42 +0100
From: Sebastian Krahmer <krahmer@...e.de>
To: oss-security@...ts.openwall.com
Subject: Re: blkid command injection
On Tue, Dec 02, 2014 at 12:22:04PM +0100, Sebastian Krahmer wrote:
>
> On Fri, Nov 28, 2014 at 12:17:24AM +1100, Murray McAllister wrote:
> > On 11/27/2014 02:25 AM, Sebastian Krahmer wrote:
> >> Hi
> >>
> >> There is a command injection inside blkid. It uses caching
> >> files (/dev/.blkid.tab or /run/blkid/blkid.tab) to store info about the
> >> UUID, LABEL etc it finds on certain devices.
> >>
> >> However, it does not strip " character, so it can be confused to
> >> build variable names containing embedded shell metas, which it would usually
> >> encode inside the value.
> >>
> >> Given an USB stick with /dev/sdb1 you can:
> >>
> >> # mkfs.ext4 -L 'X"`/tmp/foo` "' /dev/sdb1
> >> # blkid -o udev /dev/sdb1
> >> ID_FS_LABEL=X__/tmp/foo___
> >> [...]
> >>
> >> Seems to be OK, but invoking blkid a second time, taking the cache in effect:
> >>
> >> # blkid -o udev /dev/sdb1
> >> ID_FS_LABEL=X
> >> ID_FS_LABEL_ENC=X
> >> ID_FS_`/tmp/foo` "" UUID=...
> >> [...]
> >>
> >>
> >> "blkid -o udev" is often used in root context via udev or in automounters
> >> (uam-pmount) to construct key=value environment variables inside shell scripts
> >> which are then evaluated.
> >> Might be possible to construct an embedded LD_PRELOAD= as well for the binary
> >> case.
> >>
> >> By injecting > character one can probably construct whole fake cache entries.
> >>
> >> Sebastian
> >>
> >>
> >>
> >>
> >
> > Karel Zak has committed a patch:
> >
> > https://github.com/karelzak/util-linux/commit/89e90ae7b2826110ea28c1c0eb8e7c56c3907bdc
> >
>
> Thanks. Patch looks good to me. I contacted upstream about additional
> fixes which you might want to include as well, so we can release it alltogether. The
> severity of command injection is probably not that high that we need
> updates immediately.
FWIW, the issue in question can be found here:
https://bugzilla.suse.com/show_bug.cgi?id=907434
Interesting for 32 bit systems where size_t has 32bit and so a mult of two
32bit words does not fit into the result. This would allow poor-man's badUSB attacks
with lovely crafted GPT's because its probed via systemd/udev upon plugin.
Thanks to Karel Zak for fixing a wrong > in the initial patch.
Sebastian
--
~ perl self.pl
~ $_='print"\$_=\47$_\47;eval"';eval
~ krahmer@...e.de - SuSE Security Team
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