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Date: Fri, 28 Nov 2014 00:17:24 +1100
From: Murray McAllister <mmcallis@...hat.com>
To: oss-security@...ts.openwall.com
Subject: Re: blkid command injection
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
Cheers,
--
Murray McAllister / Red Hat Product Security
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