Date: Tue, 13 Apr 2004 00:00:16 +0200 From: Miroslav Lachman <000.fbsd@quip.cz> To: freebsd-security@freebsd.org Subject: fwd: mail server recommendations? Message-ID: <407B1170.8010900@quip.cz>
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Hi I am re-sending this message to this list, because freebsd-security list could be more suitable for my question about UID / GID settings of Postfix virtual users accounts. in one sentence: "If all virtual users have same UID/GID, is there some real security risk?" Thank You and I am sorry for my bad english ================================== original message from freebsd-isp: Mark Johnston wrote: > Miroslav Lachman <000.fbsd@quip.cz> wrote: > >> Hi, I am running similar configuration on several machines (Postfix + >> Courier-IMAP [with POP3ssl/IMAP4ssl] + MySQL). I have a guestion about >> one general difference - unique UID / GID for each user. I guess it >> provide more security, but also some troubles. If all virtual users >> (stored in MySQL) have same UID/GID, postfix can be configured to create >> maildirs itself with first incoming message. If each user has unique >> UID, maildirs must be created manualy (or from shellscript) and chowned >> to UID/GID. > > > > Exactly - that's the tradeoff. > > >> My question: "If all virtual users have same UID/GID, is there some real >> security risk?". > > > > Sharing UIDs and GIDs can have good or bad effects on security. On a server with no users logging in, like mine, it's moot; nobody (well, nobody who hasn't compromised the server) can get at the maildir storage on disk, so nobody (ditto) can play with the mailboxes. On a server where users do log in, you can go two routes: > > - Unique UIDs/GIDs. This makes things more convenient for the user, since they can use mail clients on the server and get right at their mail. If you want to have local mail clients work at all, you have to do this. > > - Shared UID/GID. In this case, the user can't get at their own maildir, and they'll have to use LDAP/POP3 over loopback to read their mail. It does make management easier, though. > > It sounds to me like you're working with a server where users don't log in, since you're using MySQL to manage user accounts. In that case, unique UIDs buy you essentially nothing. > Yes, I am one and only who has shell account (logging via SSH), users have FTP, POP3/IMAP/webmail, HTTP access and CVS (CVSd pserver throught SSL [stunnel]) > >> I'll be glad to read if same UID/GID is secure or not, because I am >> writing webbased administration tool in PHP and main problem is creation >> of maildirs for new accounts. Same UID/GID could solve my problem. > > > > The only time that unique UIDs and GIDs are useful is when the user will be logging in locally, so you can just look in /etc/passwd, find the user's UID, and create the maildir with that. If the user doesn't have a system account, you've got no reason to start making up UIDs to give them one; just share a single UID. > > >> PS: sorry for my bad english and a little offtopic message > > > > Since you say "offtopic", I assume you intended this for the freebsd-isp list, instead of private mail. I've taken the liberty of including the list in the Cc again, since security advice like this shouldn't go unreviewed. :) You might also want to move this thread to freebsd-security@freebsd.org, to reach people with more security know-how. > I am sorry for my mistake, I really intended this for freebsd-isp list and I'll send it to freebsd-security too. Thank you for your opinion. > >> PPS: I'll publish webbased administration tool on sourceforge.net after >> completition > > > One more question - does anybody know some webbased administration tools for email accounts of postfix virtual users in MySQL/PgSQL? (I started writing my own, but I am still interested in comparison with other tools) -- Miroslav Lachman Webapplication Developer
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