[ SOURCE: http://www.secureroot.com/security/advisories/9713650273.html ] -----BEGIN PGP SIGNED MESSAGE----- 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.html. 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.html. 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.html. 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. _________________________________________________________________ -----BEGIN PGP SIGNATURE----- Version: PGP 6.0.2 iQEVAwUBOdIIyGiN3BRdFxkbAQHiywf/XHl33Gn0t0kMW4jgeW+Ot7pHrj5m3aBX MbmVFClTUVXgA58daIH6H0PB4O5J/Qo7c6l5UH0POq1Hjd9Kog0pgDwdNomki70r QNvrlqrE3SmYtMz2OxltBQBq9mojM5/sVhdoEh/LNk693hOAYOjyrCR2Ml+avUjK IjhuMYXhoTnK5ytx/hvRmCLoqNw+GkcO885On0I0E5dQHzMWgtI3v4XGpXeWIr1R X2fMY0wwWDcfgXQQ6OkspuHcs412ukgo6hmxfEiFYVwFCiiRO7zX8tLKU5Hcc1t0 UNVsXkjPZ+sOkJxXGd4Ov7nN+DAdTrHhuJIFY5yG4ate9diT615yGQ== =bZMO -----END PGP SIGNATURE-----