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CERT Advisory 141
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=============================================================================
CERT* Advisory CA-97.09
Original issue date: April 7, 1997
Last revised: June 3, 1997
Section III.A and Appendix - Added vendor information.
for NetManage, Inc.
A complete revision history is at the end of this file.
Topic: Vulnerability in IMAP and POP
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The CERT Coordination Center has received reports of a vulnerability
in some versions of the Internet Message Access Protocol (IMAP) and
Post Office Protocol (POP) implementations (imapd, ipop2d, and
ipop3d). Information about this vulnerability has been publicly
distributed.
By exploiting this vulnerability, remote users can obtain unauthorized root
access.
The CERT/CC team recommends installing a patch if one is available or
upgrading to IMAP4rev1. Until you can do so, we recommend disabling the IMAP
and POP services at your site.
We will update this advisory as we receive additional information.
Please check our advisory files regularly for updates that relate to
your site.
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I. Description
The current version of Internet Message Access Protocol (IMAP) supports
both online and offline operation, permitting manipulation of remote
message folders. It provides access to multiple mailboxes (possibly on
multiple servers), and supports nested mailboxes as well as
resynchronization with the server. The current version also provides a
user with the ability to create, delete, and rename mailboxes. Additional
details concerning the functionality of IMAP can be found in RFC 2060
(the IMAP4rev1 specification) available from
http://ds.internic.net/rfc/rfc2060.txt
The Post Office Protocol (POP) was designed to support offline mail
processing. That is, the client connects to the server to download mail
that the server is holding for the client. The mail is deleted from the
server and is handled offline (locally) on the client machine.
In both protocols, the server must run with root privileges so it can
access mail folders and undertake some file manipulation on behalf of the
user logging in. After login, these privileges are discarded. However, a
vulnerability exists in the way the login transaction is handled, and
this can be exploited to gain privileged access on the server. By
preparing carefully crafted text to a system running a vulnerable version
of these servers, remote users may be able to cause a buffer overflow and
execute arbitrary instructions with root privileges.
Information about this vulnerability has been widely distributed.
II. Impact
Remote users can obtain root access on systems running a vulnerable IMAP
or POP server. They do not need access to an account on the system to do
this.
III. Solution
Install a patch from your vendor (see Section A) or upgrade to the latest
version of IMAP (Section B). If your POP server is based on the
University of Washington IMAP server code, you should also upgrade to
the latest version of IMAP. Until you can take one of these actions, you
should disable services (Section C). In all cases, we urge you to take
the additional precaution described in Section D.
A. Obtain and install a patch from your vendor
Below is a list of vendors who have provided information about this
vulnerability. Details are in Appendix A of this advisory; we will update
the appendix as we receive more information. If your vendor's name is not
on this list, please contact your vendor directly.
Berkeley Software Design, Inc. (BSDI)
Carnegie Mellon University
Cray Research
Digital Equipment Corporation
Linux - Caldera, Inc.
Debian
Red Hat
Microsoft Corporation
NetManage, Inc.
Netscape
QUALCOMM, Incorporated
Sun Microsystems, Inc.
University of Washington
B. Upgrade to the latest version of IMAP
An alternative to installing vendor patches is upgrading to IMAP4rev1,
which is available from
ftp://ftp.cac.washington.edu/mail/imap.tar.Z
Please note that checksums change when files are updated. The
imap.tar.Z file can undergo frequent changes, therefore the
checksums have not been included here.
C. Disable services
Until you can take one of the above actions, temporarily disable the POP
and IMAP services. On many systems, you will need to edit the
/etc/inetd.conf file. However, you should check your vendor's
documentation because systems vary in file location and the exact
changes required (for example, sending the inetd process a HUP signal or
killing and restarting the daemon).
If you are not able to temporarily disable the POP and IMAP services,
then you should at least limit access to the vulnerable services to
machines in your local network. This can be done by installing the
tcp_wrappers described in Section D, not only for logging but also for
access control. Note that even with access control via tcp_wrappers, you
are still vulnerable to attacks from hosts that are allowed to connect
to the vulnerable POP or IMAP service.
D. Additional precaution
Because IMAP or POP is launched out of inetd.conf, tcp_wrappers can be
installed to log connections which can then be examined for suspicious
activity. You may want to consider filtering connections at the firewall
to discard unwanted/unauthorized connections.
The tcp_wrappers tool is available in
ftp://info.cert.org/pub/tools/tcp_wrappers/tcp_wrappers_7.5.tar.gz
MD5 (tcp_wrappers_7.5.tar.gz) = 8c7a17a12d9be746e0488f7f6bfa4abb
Note that this precaution does not address the vulnerability described
in this advisory, but it is a good security practice in general.
...........................................................................
Appendix A - Vendor Information
Below is a list of the vendors who have provided information for this
advisory. We will update this appendix as we receive additional information.
If you do not see your vendor's name, the CERT/CC did not hear from that
vendor. Please contact the vendor directly.
Berkeley Software Design, Inc. (BSDI)
=====================================
We're working on patches for both BSD/OS 2.1 and BSD/OS 3.0 for
imap (which we include as part of pine).
Carnegie Mellon University
==========================
Cyrus Server 1.5.2, with full IMAP4rev1 and pop3 capabilities, is NOT
affected by this report and is NOT vulnerable.
Cray Research
=============
Not vulnerable.
Digital Equipment Corporation
=============================
This reported problem is not present for Digital's UNIX or
Digital ULTRIX Operating Systems Software.
Linux Systems
=============
Caldera, Inc.
-------------
On systems such as Caldera OpenLinux 1.0, an unprivileged user can
obtain root access.
As a temporary workaround, you can disable the POP and IMAP services
in /etc/inetd.conf, and then kill and restart inetd.
A better solution is to install the new RPM package that contains
the fixed versions of the IMAP and POP daemons. They are located
on Caldera's FTP server (ftp.caldera.com):
/pub/openlinux/updates/1.0/006/RPMS/imap-4.1.BETA-1.i386.rpm
The MD5 checksum (from the "md5sum" command) for this package is:
45a758dfd30f6d0291325894f9ec4c18
This and other Caldera security resources are located at:
http://www.caldera.com/tech-ref/security/
Debian
------
Debian linux is not vulnerable. For more information see
http://cgi.debian.org/www-master/debian.org/security.html
Red Hat
-------
The IMAP servers included with all versions of Red Hat Linux have
a buffer overrun which allow *remote* users to gain root access on
systems which run them. A fix for Red Hat 4.1 is now available
(details on it at the end of this note).
Users of Red Hat 4.0 should apply the Red Hat 4.1 fix. Users of previous
releases of Red Hat Linux are strongly encouraged to upgrade or simply
not run imap. You can remove imap from any machine running with Red
Hat Linux 2.0 or later by running the command "rpm -e imap", rendering
them immune to this problem.
All of the new packages are PGP signed with Red Hat's PGP key,
and may be obtained from ftp.redhat.com:/updates/4.1. If
you have direct Internet access, you may upgrade these packages on your
system with the following commands:
Intel:
rpm -Uvh ftp://ftp.redhat.com/updates/4.1/i386/imap-4.1.BETA-3.i386.rpm
MD5 (imap-4.1.BETA-3.i386.rpm) = 8ac64fff475ee43d409fc9776a6637a6
Alpha:
rpm -Uvh ftp://ftp.redhat.com/updates/4.1/alpha/imap-4.1.BETA-3.alpha.rpm
MD5 (imap-4.1.BETA-3.alpha.rpm) = fd42ac24d7c4367ee51fd00e631cae5b
SPARC:
rpm -Uvh ftp://ftp.redhat.com/updates/4.1/sparc/imap-4.1.BETA-3.sparc.rpm
MD5 (imap-4.1.BETA-3.sparc.rpm) = 751598aae3d179284b8ea4d7a9b78868
Microsoft
=========
Microsoft's Exchange POP and IMAP servers and Microsoft's Commericial
Internet System are not vulnerable
NetManage, Inc.
=========
NetManage's ZPOP pop server is not vulnerable.
Netscape
========
Netscape's POP3/IMAP4 implementation is not vulnerable.
QUALCOMM Incorporated
======================
Our engineers have examined the QPopper source code, which is based
on source from UC Berkeley. They determined that QPopper is *NOT*
vulnerable to a buffer overflow attack as described in CA-97.09.
It strictly checks the size of messages before copying them into its
buffer.
Sun Microsystems, Inc.
======================
Not vulnerable.
University of Washington
========================
This vulnerability has been detected in the University of Washington c-client
library used in the UW IMAP and POP servers. This vulnerability affects all
versions of imapd prior to v10.165, all versions of ipop2d prior to 2.3(32),
and all versions of ipop3d prior to 3.3(27).
It is recommended that all sites using these servers upgrade to the
latest versions, available in the UW IMAP toolkit:
ftp://ftp.cac.washington.edu/mail/imap.tar.Z
Please note that checksums change when files are updated. The
imap.tar.Z file can undergo frequent changes, therefore the checksums
have not been included here.
This is a source distribution which includes imapd, ipop2d, ipop3d. and
the c-client library. The IMAP server in this distribution conforms with
RFC2060 (the IMAP4rev1 specification).
Sites which are not yet prepared to upgrade from IMAP2bis to IMAP4
service may obtain a corrected IMAP2bis server as part of the latest
(3.96) UW Pine distribution, available at:
ftp://ftp.cac.washington.edu/pine/pine.tar.Z
MD5 (pine.tar.Z) = 37138f0d1ec3175cf1ffe6c062c9abbf
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The CERT Coordination Center thanks the University of Washington's
Computing and Communications staff for information relating to this
advisory. We also thank Wolfgang Ley of DFN-CERT for his input. We
thank Matthew Wall of Carnegie Mellon University for additional
insightful feedback.
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If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident Response
and Security Teams (see http://www.first.org/team-info)
CERT/CC Contact Information
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Email cert@cert.org
Phone +1 412-268-7090 (24-hour hotline)
CERT personnel answer 8:30-5:00 p.m. EST(GMT-5) / EDT(GMT-4)
and are on call for emergencies during other hours.
Fax +1 412-268-6989
Postal address
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
USA
Using encryption
We strongly urge you to encrypt sensitive information sent by email. We can
support a shared DES key or PGP. Contact the CERT/CC for more information.
Location of CERT PGP key
ftp://info.cert.org/pub/CERT_PGP.key
Getting security information
CERT publications and other security information are available from
http://www.cert.org/
ftp://info.cert.org/pub/
CERT advisories and bulletins are also posted on the USENET newsgroup
comp.security.announce
To be added to our mailing list for advisories and bulletins, send
email to
cert-advisory-request@cert.org
In the subject line, type
SUBSCRIBE your-email-address
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Copyright 1997 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and the copyright statement is
included.
* Registered in the U.S. Patent and Trademark Office.
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This file: ftp://info.cert.org/pub/cert_advisories/CA-97.09.imap_pop
http://www.cert.org
click on "CERT Advisories"
===========================================================================
UPDATES
April 8, 1997
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We have received requests for clarification. The vulnerability
described in this advisory relates to certain server implementations
and is not in the protocol itself. See Appendix A for vendor and
server information.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history
June 3, 1997 Section III.A and Appendix - Added vendor information.
for NetManage, Inc.
May 1, 1997 Section III.A and Appendix A - Added vendor information
for Microsoft Corporation.
Apr 18, 1997 Section III.A and Appendix A - Added vendor information
for Debian and Netscape.
Apr 11, 1997 Section III.B. - Removed checksum information for the
imap.tar.Z distribution and added an explanation.
Apr 9, 1997 Appendix A - added vendor information for Digital Equipment
Corporation and QUALCOMM Incorporated.
Updated vendor information for Sun Microsystems, Inc.
Added another name to acknowledgment.
Apr 08, 1997 Updates - Added clarification that the vulnerability
is an implementation error and not an error in the protocol
Appendix - added vendor information for Caldera and the
Carnegie Mellon University Cyrus Server
Acknowledgments - Added a name that was inadvertently left out
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