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Cisco Security Advisory: Cisco Secure PIX Firewall Mailguard Vulnerability
From: Cisco Systems Product Security Incident Response Team <psirt () cisco com>
Date: Wed, 27 Sep 2000 08:10:00 -0700

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               Cisco Secure PIX Firewall Mailguard Vulnerability

Revision 1.0

  For public release 2000 Sept 27 08:00 AM 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.

   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(5), 5.0(3), 5.1(2) and 5.2(1) 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(5) (including 2.7,   | 4.4(6)                           |
   | 3.0, 3.1, 4.0, 4.1)                 |                                  |
   +-------------------------------------+----------------------------------+
   | Version 5.0.x up to and including   |                                  |
   | version 5.0(3)                      | 5.1(3)                           |
   +-------------------------------------+----------------------------------+
   | All 5.1.x up to and including       |                                  |
   | version 5.1(2)*                     | 5.1(3)                           |
   +-------------------------------------+----------------------------------+
   | Version 5.2(1)                      | 5.2(2)                           |
   +-------------------------------------+----------------------------------+

   *For customers who may have engineering releases addressing specific
   unrelated defects, designated as 5.1(2)2xx, version 5.1(3) 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(2)207 or higher, which also
   includes the SMTP security 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: 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 1.0  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.
     _________________________________________________________________


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