Re: Mac symlink attack techniques?

[Jon Hart <jhart () spoofed org>]

On Sat, Apr 12, 2008 at 12:35:49PM -0400, Paul Melson wrote:
> You can create /etc/rc.installer_cleanup which typically doesn't
> usually exist, but if it does is run by init to complete software
> installs after reboot.
> If you are able to also force a reboot (or even count on one occurring
> at a certain time), it's pretty much game over.

Good suggestion.  However, /etc/rc.installer_cleanup must be executable
because it is called as so from /etc/rc:
 
if [ -f /etc/rc.installer_cleanup ]; then
        /etc/rc.installer_cleanup multiuser
fi

In this particular situation, the files are created 666 exlusively, so
a symlink attack that writes /etc/rc.installer_cleanup will not be
a viable exploit route.  At least not directly.  

What makes this more difficult is that if the target of a symlink
already exists, the vulnerable application preserves its permissions so
the 666 permissions cannot be exploited.

Thanks for your input,

-jon

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