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Re: Which checks should we mandate for source operations in shell scripts




On Wed, 20 Jun 2018 at 21:49:29 +0200, Marc Haber wrote:
> It has (finally, and to late) occurred to me that
> 
> |# back up /etc/default/foo
> |cp /etc/default/foo ~/foo
> |(try something in /etc/default)
> |sudo mv ~/foo /etc/default/foo
> 
> will place a file owned by my "normal" user into /etc/default where it
> might be used from an (unchanged) init script[1].

If you can do that, then your normal user has already escalated privileges
to execute arbitrary code (in this case mv) as root, so I'm not sure
that it's a new thing that the same user can repeat that escalation?
Either your user account is trusted to execute code of their choice as
root or they aren't.

(Yes, sudo prompts for a password, which puts a small barrier between
"your normal user" and "your normal user, sudoing"; but if a hostile
actor ever gains control over your normal user account, there are various
things they can do to escalate from there to having control over the
sudoing state of your normal user account, for example putting a sudo
on your $PATH that logs your password for next time or making sudo an
alias for a similar trojaned sudo binary.)

For your use-case above, I'd suggest sudoedit(8), which copies the file
to be edited into /var/tmp, runs your $EDITOR as you, and if the file
was modified by the time your editor exits, copies it back.

    smcv