Using exec() in PHP as an specific system user

Question

When I use the following php script:

<?php
    echo 'I am '.exec('whoami').' user';
?>

on my localhost, the result is I am nobody user and is what I expect.

But when I use:

<?php
    echo 'I am '.exec('echo <PASSWD> | sudo -S -u <USER> whoami').' user';
?>

where <PASSWD> is my password and <USER> is my user name, the result is I am user and I expect to be I am <USER> user. How can I make it to work as I wish?

As a note, when I use echo 'I am '.exec('echo <PASSWD> | sudo -S -u <USER> whoami').' user'; inside php interpreter (php -a), everything is fine.

Matthew R. · Accepted Answer · 2013-08-13 19:19:42Z

1

The user that is being used is the one running php/httpd process on the server. Depending on your server setup this could be Apache, root, or in FastCGI setups it can be any user or no user. This is a fallacy since there must always be a user. Typically shared hosting servers will try to circumvent allowing users to execute functions as a sudo user. This may be what you are experiencing.

answered Aug 13, 2013 at 19:19

Matthew R.

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2 Comments

Radu Rădeanu Over a year ago

Ok, this I experiecing. But my question is how can I make it to work (if there is a way)... When I use php interpreter is working.

Matthew R. Over a year ago

Unfortunately, in this context, whoami will always return the user that is running the service, regardless of the username you are logged in with. The reason is because you are not running the script from a shell like you typically would, you are running the script from the server. The server is always the same user, so it will always be that. You could try using something like PHP's FTP functions or PHPSECLIB to connect from your script and print the user/pass.

Owen Beresford · Accepted Answer · 2013-08-13 21:17:11Z

0

A straight answer is you may need to go via shell to use the pipes etc

shell_exec..

For large scale applications, creating all those small processes is quite expensive.

IMO, a better solution is using these ::

pcntl_fork
posix_seteuid
posix_setegid
exec
Optional proc_nice

The calls to sudo are technically running with root permission. So this is the same, in a more visible fashion..

I'm sure you don't need me to tell you that putting those passwords in your source is a bad idea.

answered Aug 13, 2013 at 21:17

Owen Beresford

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