-----BEGIN PGP SIGNED MESSAGE----- Cisco Secure PIX Firewall SMTP Filtering Vulnerability ========================================================================= Version 1.0 For Public Release 2001 September 26 08:00 AM US/Pacific (UTC+0800) ------------------------------------------------------------------------ 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 CSCdu47003. The complete notice will be available at http://www.cisco.com/warp/public/707/PIXfirewallSMTPfilter-regression-pub.shtml. Affected Products ================= All users of Cisco Secure PIX Firewalls with software versions 6.0(1), 5.2(5) and 5.2(4) that provide access to SMTP Mail services are at risk. Please see the table below for affected versions. The IOS Firewall feature set is not affected by the above defect. Details ======= The behavior is a failure of the command fixup protocol smtp [portnum], which is enabled by default on the Cisco Secure PIX Firewall. The impact and description of this defect is similar to a defect outlined in a previous security advisory, http://www.cisco.com/warp/public/707/PIXfirewallSMTPfilter-pub.shtml, however, this instance of mail filtering bypass was re-introduced by the defect CSCds90792. If you do not have protected Mail hosts with the accompanying configuration (configuration example below) you are not vulnerable to the attack. 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 ====== If the mail server itself is not properly secured, an attacker may be able to collect information about existing e-mail accounts and aliases, or may be able to execute arbitrary code on the mail server. 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. Please note that Cisco strongly recommends that security on all servers, workstations and network infrastructure gear is maintained as part of Standard Operating Procedures. Internet Firewalls do not protect against risk factors internal to a Firewalled network such as social engineering, rogue internal users or additional external access points to the internal network (i.e. modem pools or network fax machines) and as such should not be viewed as the only security measure necessary to ensure network integrity. Software Versions and Fixes =========================== Fixed Regular Interim Release Release; available Version Affected Fix will carry now forward into all Fix will carry later versions forward into all later versions 4.4(7.202) 4.4(7.204) 4.4(8) 5.1(4.206) 5.1(4.209) 5.1(5) 5.2(3.210) 5.2(5.207) 5.2(6) 5.3(1.200) 5.3(1.206) 5.3(2) 6.0(1) 6.0(1.101) 6.1(1) Obtaining 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 above, 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. 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 whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for assistance with the upgrade, which should be free of charge. Customers who purchase direct from Cisco but who do not hold a Cisco service contract, and customers who purchase through third party vendors but are unsuccessful at obtaining fixed software through their point of sale, 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: tacat_private 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 "psirtat_private" or "security-alertat_private" for software upgrades. Workarounds =========== There is not a direct workaround 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 discovered internally by Cisco, during expanded regression testing. This vulnerability has been discussed on public forums previously. This vulnerability has not been discussed recently, and has not been discussed with reference to the current versions of the PIX software. Status of This Notice: FINAL ============================ This is a final 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-regression-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-announceat_private * bugtraqat_private * first-teamsat_private (includes CERT/CC) * ciscoat_private * comp.dcom.sys.cisco * firewallsat_private * 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 For public release 26-SEP-2001 08:00 AM US/Pacific (UTC-0800) 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. All Cisco Security Advisories are available at http://www.cisco.com/go/psirt. ------------------------------------------------------------------------ This notice is Copyright 2001 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, and include all date and version information. ------------------------------------------------------------------------ -----BEGIN PGP SIGNATURE----- Version: PGP 7.0 iQEVAwUBO7H48Q/VLJ+budTTAQEGXggAhYoTXPsbs+HxytSUN/J+KxDklA+FHh25 vO/nKC0yVuVYs/E+FXrfSK0tI8VEezk/vfCbur/7DG4xmZRtiEWTeTZbQ5gsT1vz HURo8kT8r8ta2zTg0TlhCiUSkMZ6ySshHTtyeIwd3NvK1AQxe2pLJU9l5KYHyBwk iYwpUQdq4p57db5fPtzZMyfDG9GClw+5vNsdt635k3E95iLXo3zUr388aPWEzh5L dKPQbqakXNrjO91ra5YyAVeGHWCjfisOb0qnBmZ5E9DV3ETmykB6sl/rTOgMhD2I ivxa0ky4hq+OKZjKNg9rSM+a/zqRgDGgmFSG5yJqIn5r6f4k3FChlA== =qnTL -----END PGP SIGNATURE-----
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