Hello Matt,
Indeed FreeBSD doesn't respect the cases where a shell script is on a
noexec mounted device; but where /bin/sh is still executable (/bin/sh
/tmp/script for example). From the Manual page this should be clear that
it is not designed as a security measure but to aid other activities; it
is unlikely that we (see the archives for more information, this had been
discussed a couple of times) will change this behaviour (since the design
isn't for
security):
mount(8):
noexec Do not allow execution of any binaries on the mounted
file system. This option is useful for a server that
has
file systems containing binaries for architectures other
than its own. Note: This option was not designed as a
security feature and no guarantee is made that it will
prevent malicious code execution; for example, it is
still possible to execute scripts which reside on a
noexec mounted partition.
Hope this helps aiding you a bit with the information we can deliver.
Regards,
Remko
On Mon, June 18, 2007 6:47 pm, Matt D. Harris wrote:
They're being executed despite filesystem mount options because the
script isn't being executed, the perl interpretter is. The script is
being read and interpretted by the perl interpretter. Interesting - I
hadn't thought of this before. Some logic to check the underlying
filesystem of a script before reading it would be a very cool addition
to perl from a security standpoint. Wouldn't be a big performance hit
at all just to check once every require, etc as well. It'd need to be
somewhat platform specific. Anyways, it would be neat for someone to
bring this up within the Perl community as a possible idea, and maybe
consider python, ruby, and others as well. Then there're various
shells... I tested bash and FreeBSD's /bin/sh, and neither of them
respect the noexec mount flag on FreeBSD either. It seems like this
should be a relatively easy problem to correct, at least for the most
common platforms. It's a thought that I'm going to bring up with the
FreeBSD guys and see what their reaction is. Thanks for bringing this
up here. Take care, Matt
kladizkov.thehome wrote:
Hi,
My firewall LFD, pulled out three perl scripts from /tmp. It was found
to be executing in my server. I have attached the scripts along with
this mail. Is this issue familiar to anyone?
How can a script uploaded to /tmp be executed when it has noexec
privilege?
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IDS
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Kind regards,
Remko Lodder ** remko@elvandar.org
FreeBSD ** remko@FreeBSD.org
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