Date: Mon, 24 Apr 2000 15:46:34 -0700
From: FreeBSD Security Officer [email protected]
To: [email protected]
Subject: FreeBSD Security Advisory: FreeBSD-SA-00:14.imap-uw
FreeBSD-SA-00:14 Security Advisory
FreeBSD, Inc.
Topic: imap-uw contains security vulnerabilities for "closed"
mail servers
Category: ports
Module: imap-uw
Announced: 2000-04-24
Credits: Michal Zalewski [email protected]
Michal Szymanski [email protected] via BugTraq
Affects: Ports collection.
Corrected: See below.
Vendor status: Aware of the problem, no satisfactory solution provided.
FreeBSD only: NO
I. Background
imap-uw is a popular IMAP4/POP2/POP3 mail server from the
University of Washington.
II. Problem Description
There are numerous buffer overflows available to an imap user
after they have successfully logged into their mail account (i.e.
authenticated themselves by giving the correct password, etc). Once
the user logs in, imapd has dropped root privileges and is running
as the user ID of the mail account which has been logged into, so
the buffer overflow can only allow code to be executed as that
user.
Thus, the vulnerability is only relevant on a “closed” mail
server, i.e. one which does not normally allow interactive logins
by mail users. For a system which allows users to log in or execute
code on the system, there is minimal vulnerability.
Note that once a user has successfully exploited the
vulnerability to gain access to their user account they may be able
to mount further attacks against the local (or a remote) machine to
upgrade their privileges.
The imap-uw port is not installed by default, nor is it “part of
FreeBSD” as such: it is part of the FreeBSD ports collection, which
contains over 3200 third-party applications in a ready-to-install
format. The ports collection shipped with FreeBSD 4.0 contains this
problem since it was discovered after the release.
FreeBSD makes no claim about the security of these third-party
applications, although an effort is underway to provide a security
audit of the most security-critical ports.
III. Impact
A user with a mail account on the imap server can execute
arbitrary code as themselves on that machine. This is only likely
to be a security issue on “closed” mail servers which do not allow
interactive shell logins.
Only imapd is known to be vulnerable to this time – the other
daemons installed by the imap-uw port (ipop2d/ipop3d) are not known
to suffer from the same vulnerability.
If you have not chosen to install the imap-uw port/package, then
your system is not vulnerable to this problem.
IV. Workaround
1) Deinstall the imap-uw port/package, if you you have installed
it.
2) If you do not specifically require imap functionality (i.e.
pop2/pop3 is sufficient) then disable the imap daemon in
/etc/inetd.conf and restart inetd (e.g. with the command ‘killall
-HUP
inetd’)
V. Solution
Unfortunately the vulnerabilities in imapd are quite extensive
and no patch is currently available to address them. There is also
no “drop-in” replacement for imap-uw currently available in ports,
although the mail/cyrus port is another imap server which may be a
suitable replacement. Cyrus has different configuration and
operational requirements than imap-uw however, which may make it
unsuitable for many users.
Until a security audit of the imap-uw source can be completed
and the vulnerabilities patched, it is recommended that operators
of “closed” imapd servers take steps to minimize the impact of
users being able to run code on the server (i.e., by tightening the
local security on the machine to minimize the damage an intruding
user can cause).
This advisory will be updated once the known vulnerabilities in
imap-uw have been addressed.