__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Cisco Secure PIX Firewall Mailguard Vulnerability October 11, 2000 21:00 GMT Number L-002 ______________________________________________________________________________ PROBLEM: A feature of the Cisco Secure PIX Firewall, "Mailguard", has a vulnerability. This vulnerability can be exploited to bypass SMTP command filtering. PLATFORM: Cisco Secure PIX Firewalls with versions up to and including 4.4(6), 5.0(3), 5.1(3) and 5.2(2). This vulnerability only exists if access to SMTP Mail services is provided by the Firewall. DAMAGE: Exploitation of the mail server is possible if the PIX firewall has been configured in a specific manner. Exploitation of the "Mailguard" feature effectively removes firewall protection for the mail server. Failure of the Mailguard command "fixup protocol smtp [portnum]" is responsible for the firewall failure. This command is enabled by default on the firewall. SOLUTION: The "Mailguard" feature incorporated into the firewall is a protection feature for weakly protected mailservers. The first stage protection should always be the fortification of the mailserver against intruders. The PIX firewall offers extra protection of the server. Cisco recommends that mailserver security features be fortified, or follow the advisory instructions for upgrading the PIX firewall code. Best operating practice is to do both. ______________________________________________________________________________ VULNERABILITY The risk is LOW. A malicious user would have to gain direct ASSESSMENT: access to a mailserver for exploitation to occur. The risk is further minimized if security measures have been taken on the server to protect it. ______________________________________________________________________________ [****** Begin Cisco Advisory ******] Cisco Security Advisory: Cisco Secure PIX Firewall Mailguard Vulnerability Revision 1.1 Updated, for public release 2000 October 5 04:00 PM US/Pacific (UTC+0700) _________________________________________________________________ Summary The Cisco Secure PIX firewall feature "mailguard," which limits SMTP commands to a specified minimum set of commands, can be bypassed. This vulnerability can be exploited to bypass SMTP command filtering. This vulnerability has been assigned Cisco bug ID CSCdr91002 and CSCds30699. A new aspect of this vulnerability has been assigned Cisco bug ID CSCds38708. The complete advisory is available at http://www.cisco.com/warp/public/707/PIXfirewallSMTPfilter-pub.shtml. Affected Products All users of Cisco Secure PIX Firewalls with software versions up to and including 4.4(6), 5.0(3), 5.1(3) and 5.2(2) that provide access to SMTP Mail services are at risk. The IOS Firewall featureset is not affected by either of the above defects. Details The behavior is a failure of the command "fixup protocol smtp [portnum]", which is enabled by default on the Cisco Secure PIX Firewall. If you do not have protected Mail hosts with the accompanying configuration (configuration example below) you are not affected by this vulnerability. To exploit this vulnerability, attackers must be able to make connections to an SMTP mail server protected by the PIX Firewall. If your Cisco Secure PIX Firewall has configuration lines similar to the following: fixup protocol smtp 25 and either conduit permit tcp host 192.168.0.1 eq 25 any or conduit permit tcp 192.168.0.1 255.255.255.0 eq 25 any or access-list 100 permit tcp any host 192.168.0.1 eq 25 access-group 100 in interface outside The expected filtering of the Mailguard feature can be circumvented by an attacker. Impact The Mailguard feature is intended to help protect weakly secured mail servers. The workaround for this issue is to secure the mail servers themselves, or upgrade to fixed PIX firewall code. In order to exploit this vulnerability, an attacker would need to also exploit the mailserver that is currently protected by the PIX. If that server is already well configured, and has the latest security patches and fixes from the SMTP vendor, that will minimize the potential for exploitation of this vulnerability. Software Versions and Fixes Getting Fixed Software Cisco is offering free software upgrades to remedy this vulnerability for all affected customers. Customers with service contracts may upgrade to any software version. Customers without contracts may upgrade only within a single row of the table below, except that any available fixed software will be provided to any customer who can use it and for whom the standard fixed software is not yet available. As always, customers may install only the feature sets they have purchased. +-------------------------------------+----------------------------------+ | | Fixed Regular Release available | | Version Affected | now; fix will carry forward into | | | all later releases | +-------------------------------------+----------------------------------+ | All versions of Cisco Secure PIX up | | | to version 4.4(6) (including 2.7, | 4.4(7) | | 3.0, 3.1, 4.0, 4.1) | | +-------------------------------------+----------------------------------+ | Version 5.0.x up to and including | | | version 5.0(3) | 5.1(4) | +-------------------------------------+----------------------------------+ | All 5.1.x up to and including | | | version 5.1(3)* | 5.1(4) | +-------------------------------------+----------------------------------+ | Version 5.2(2) | 5.2(3) | +-------------------------------------+----------------------------------+ *For customers who may have engineering releases addressing specific unrelated defects, designated as 5.1(2)2xx, version 5.1(4) only includes the SMTP security fixes and does not include any other bugfixes. Customers requiring engineering releases to address specific unrelated defects will need to use 5.1.4(200) or 4.4.7(200), which include all SMTP vulnerability fixes. Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained via the Software Center on Cisco's Worldwide Web site at http://www.cisco.com. Customers without contracts should get their upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC contacts are as follows: * +1 800 553 2447 (toll-free from within North America) * +1 408 526 7209 (toll call from anywhere in the world) * e-mail: tac@cisco.com Give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC. Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades. Workarounds There is not a direct work around for this vulnerability. The potential for exploitation can be lessened by ensuring that mail servers are secured without relying on the PIX functionality. Exploitation and Public Announcements This vulnerability was first reported to Cisco by a customer. This vulnerability has been discussed on public forums. Status of This Notice: Revised FINAL This is a final field notice. Although Cisco cannot guarantee the accuracy of all statements in this notice, all of the facts have been checked to the best of our ability. Cisco does not anticipate issuing updated versions of this notice unless there is some material change in the facts. Should there be a significant change in the facts, Cisco may update this notice. Distribution This notice will be posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/PIXfirewallSMTPfilter-pub.shtml. In addition to Worldwide Web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients: * cust-security-announce@cisco.com * bugtraq@securityfocus.com * first-teams@first.org (includes CERT/CC) * cisco@spot.colorado.edu * comp.dcom.sys.cisco * firewalls@lists.gnac.com * Various internal Cisco mailing lists Future updates of this notice, if any, will be placed on Cisco's Worldwide Web server, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the URL given above for any updates. Revision History Revision 1.1 05-OCT-2000 New defect ID reference, and revised the Fixed in versions to reflect recent fixes. Revision 1.0 27-SEP-2000 Initial Public Release Cisco Security Procedures Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/sec_incident_response.shtml. This includes instructions for press inquiries regarding Cisco security notices. _________________________________________________________________ This notice is copyright 2000 by Cisco Systems, Inc. This notice may be redistributed freely after the release date given at the top of the text, provided that redistributed copies are complete and unmodified, including all date and version information. [****** End Cisco Advisory ******] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Cisco Systems, Inc. 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. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@llnl.gov For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), use one of the following methods to contact CIAC: 1. Call the CIAC voice number 925-422-8193 and leave a message, or 2. Call 888-449-8369 to send a Sky Page to the CIAC duty person or 3. Send e-mail to 4498369@skytel.com, or 4. Call 800-201-9288 for the CIAC Project Leader. Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ (or http://ciac.llnl.gov -- they're the same machine) Anonymous FTP: ftp.ciac.org (or ciac.llnl.gov -- they're the same machine) Modem access: +1 (925) 423-4753 (28.8K baud) +1 (925) 423-3331 (28.8K baud) PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. 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