__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Vulnerability in IMAP and POP April 10, 1997 17:00 GMT Number H-46 ______________________________________________________________________________ PROBLEM: A vulnerability has been reported in some versions of the Internet Message Access Protocol (IMAP) and Post Office Protocol (POP) implementations (imapd, ipop2d, and ipop3d). PLATFORM: See "Appendix A - Vendor Information" below for platforms effected. DAMAGE: By exploiting this vulnerability, may allow remote users can obtain unauthorized root access. SOLUTION: Implement the following: 1) Obtain and install patch from your vendor, 2) Upgrade to the latest version of IMAP, or 3) Disable services. ______________________________________________________________________________ VULNERABILITY Information about this vulnerability has been publicly ASSESSMENT: distributed. ______________________________________________________________________________ [Start of CERT Advisory] ============================================================================= CERT* Advisory CA-97.09 Original issue date: April 7, 1997 Last revised: April 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. Topic: Vulnerability in IMAP and POP ------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------ 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 - Red Hat Caldera, Inc. 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 MD5 (imap.tar.Z) = 87329f3f87909fe29d5d0b1b10f22ee9 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/ 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 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 MD5 (imap.tar.Z) = fb94453e8d2ada303e2db8d83d54bfb6 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 ------------------------------------------------------------------------------ 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. ------------------------------------------------------------------------------ [End of CERT Advisory] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of CERT for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. 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