SECURITY.NNOV: Courier CPU exhaustion + bonus on imap-uw

2002-06-01T00:00:00
ID SECURITYVULNS:DOC:3021
Type securityvulns
Reporter Securityvulns
Modified 2002-06-01T00:00:00

Description

Imap-uw allows user to access any file he could access locally. It's not a bug it's insecurity by design. According to vendor's web FAQ (it's not pointed in FAQ inside program distribution):

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5.1 I see that the IMAP server allows access to arbitary files on the system, including /etc/passwd! How do I disable this?

You should not worry about this if your IMAP users are allowed shell access. The IMAP server does not permit any access that the user can not have via the shell. If, and only if, you deny your IMAP users shell access, you may want to consider one of three choices. Note that these choices reduce IMAP functionality, and may have undesirable side effects. Each of these choices involves an edit to file src/osdep/unix/env_unix.c

The first (and recommended) choice is to set restrictBox as described in file CONFIG. This will disable access to the filesystem root, to other users' home directory, and to superior directory.

The second (and strongly NOT recommended) choice is to set closedBox as described in file CONFIG. This puts each IMAP session into a so-called "chroot jail", and thus setting this option is extremely dangerous; it can make your system much less secure and open to root compromise attacks. So do not use this option unless you are absolutely certain that you understand all the issues of a "chroot jail."

The third choice is to rewrite routine mailboxfile() to implement whatever mapping from mailbox name to filesystem name (and restrictions) that you wish. This is the most general choice. As a guide, you can see at the start of routine mailboxfile() what the restrictBox choice does.

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It should be noted that neither restrictBox nor closedBox is not described at file CONFIG at all (as for imap-2001a)... And even if you smart enough to check the FAQ on the web site after you red the FAQ in source distribution restrictBox can be bypassed in case of any Windows builds (for example http://sourceforge.net/projects/uw-imap-cygwin/) because '\\' symbol is never checked. Hope nobody uses UW under NT or a version from OS ports distribution in production environment because as far as I can see port maintainers do not change the value of closedBox :).

Quite dangerous default feature anyway because some providers use imap-uw to allow imap access for customers.

I don't know any utilities to access filesystem via imap-uw, so I decided to write my own. You can download http://www.security.nnov.ru/imaptools.tgz.

it includes:

imapget.c - to retrieve file via imap-uw, usage example: imapget imap.host.name /etc/passwd > passwd it should work for both text and binary files.

imapls.c - to get a file listing, usage example: imapls imaphostname /tmp/\* > ls-tmp

imaprm.c, imapmkdir.c - hope you catch the idea.