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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