On 10/28/2013 03:14 PM, Douglas Mortensen wrote:
If a customer has vulnerable PHP code on a website, some of these will allow a remote file upload. I have seen cases where they upload a PHP script that is a sort of web-based console/shell to the server (file-system, etc.). It provides several tools which all run through the uploaded PHP script to try to brute force and do other attacks. I've seen attempts at a root exploit. We've never had a root exploit and any such case of a customer's site being hacked has been easily contained by simple filesystem permissions being correct (and the fact that we have apache setup to run all scripts as the user who is the owner of the script files, which confines the script to that users' permissions). Still nobody loves the idea of bad guys trying to hack on your box.
If an attacker gets root, the entire exercise is pointless, because he can get the decryption key. So you "don't have to worry" about that case =)
A suggestion, not dovecot-related:
The web users -- in our case, www.example.com -- shouldn't have access to anything outside of the web root. You can achieve this within PHP by placing everything that the website will need under one directory, and setting (in apache):
php_admin_value open_basedir /var/www/$domain/$host/ php_admin_value upload_tmp_dir /var/www/$domain/$host/tmp php_admin_value session.save_path /var/www/$domain/$host/tmp php_admin_value sys_temp_dir /var/www/$domain/$host/tmp
Personally, I don't trust PHP at all, so we create a separate web user for each vhost and run them under mpm-itk http://mpm-itk.sesse.net/.
So.... given that type of scenario, if filesystem permissions weren't correct, or some new exploit surfaced that allowed someone bypass or elevate to root, then they could theoretically have access to the entire fileystem including where emails are stored.
Who has access to the maildirs on your systems? On ours, everything is owned by deliver:deliver, with mode 700 or 600. The dovecot 'deliver' user is the one who reads and writes all mail. (It is in fact a misnomer now that we use LMTP). You can achieve the same by setting mode=600 everywhere in dovecot.conf, but this depends on your setup.
Suppose someone gains access to the 'deliver' user. That user is the one who reads and would decrypt the mail; therefore the attacker can read the mail anyway. But if they don't gain access to the 'deliver' account, what can they do? Barring incorrect permissions or a kernel bug, nothing.
The permissions are handled by dovecot, which ostensibly you trust. And if there's a kernel bug, you have bigger problems.