full-disclosure - Symlink attack techniques

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Date: Fri Dec 16 00:44:33 2005
From: tim-security at sentinelchicken.org (Tim)
Subject: Symlink attack techniques

> Ok I should have been more precise in my previous mail. In this scenario I 
> don't have control over the output generated by the find command. So 
> basically the cronjob is something like:
> 
> 15 4 ?* * 6 ?root ?/usr/bin/find /home/userA -type f -print > /tmp/report.txt
> 
> Consequently as userB I have no way of influencing what information is printed 
> by the find command to /tmp/report.txt but I can surely 
> control /tmp/report.txt. Any other ideas of how to exploit this to gain root 
> access?

hmmmm, as userB, you do have a way to influence userA's files.  It's
staring you right in the face.

Symlink /tmp/report to a malicious filename under /home/userA, much like
H D Moore suggested.

Then, before the next cronjob runs, re-symlink it to a script that will
execute your command.

Never tried something like that, but with enough hackery, it seems like
it could work.

good luck,
tim