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Re: Email based attack on University

On 8/10/19 12:45 am, Jonathan Dowland wrote:
On Mon, Oct 07, 2019 at 10:49:01AM +1100, Keith Bainbridge wrote:
Well I think the bash line means that the bash command uses ~/whatever as data (which it could do without the x switch?) like any program does with data files. I wasn't aware of this. I read later the the -c is not necessary, and wonder if the "s are necessary.

The quotes are only necessary if the path to the binary you want to
invoke are necessary. I use them out of habit, although I forgot that
'~' is not expanded within quotes. Using "$HOME/whatever" instead would
have worked.

-c is key here, because I'm not assuming that ~/whatever is a shell
script. This is telling the shell interpreter to run the command,
whatever it may be. But, as pointed out elsewhere, "noexec" does indeed
defeat running a binary via bash in this exact manner.

The 3rd suggestion is still a mystery.

That's a loader binary that loads and executes a binary supplied as an
argument. It's actually invoked under the hood whenever you run a
binary. But again as pointed out elsewhere "noexec" defeats this direct
approach; one needs to introduce more indirection.

Thankyou Jonathan.

So I put noexec under the heading of it may deter somebody who is looking for easy targets.

bash without the -c will run a script however.

Now to make that info useful. I have back-up disks mount noexec and then unmount as part of the script. BUT I've had a couple of instances of the back landing in the mount point for some reason. If the script is on the disk, it can only run if the disk mounts, surely. So now is the time to check it all out

Again, thanks for persisting.

Keith Bainbridge

+61 (0)447 667 468

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