-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Cisco Response ============== This is Cisco PSIRT's response to the statements made by Arhont Ltd. in their message: Making unidirectional VLAN and PVLAN jumping bidirectional, posted on 2005-Dec-19. An archived version of the report can be found here: http://lists.grok.org.uk/pipermail/full-disclosure/2005-December/ 040333.html Cisco confirms the statements made. We would like to thank Arhont Ltd. for reporting this issue to us. We greatly appreciate the opportunity to work with researchers on security vulnerabilities, and welcome the opportunity to review and assist in product reports. Additional Information ====================== Cisco is aware of VLAN spoofing attacks and recommends that customers apply best practices where possible to reduce the impact of such attacks on their networks. Many best practices are discussed in Cisco's SAFE Blueprint for Layer 2 security: http://www.cisco.com/en/US/netsol/ns340/ns394/ns171/ns128/ networking_solutions_white_paper09186a008014870f.shtml As mentioned in the Arhont advisory, this is a protocol issue with 802.1q VLANS, and not a vendor-specific issue. However, there are techniques available on Cisco devices that may allow you to reduce your exposure to the mentioned attacks. The Cisco SAFE Blueprint for Layer 2 security discusses double tagging attacks here: http://www.cisco.com/en/US/netsol/ns340/ns394/ns171/ns128/ networking_solutions_white_paper09186a008014870f.shtml#wp1002270 The recommended configuration is to disable 802.1q trunking everywhere it is not required so that tagged frames are discarded on ports not configured for trunking. The publication by Arhont also leverages an IP spoofing component to enable the attack. Cisco recommends IP anti-spoofing techniques and features such as Unicast Reverse Path Forwarding (uRPF) to guard against spoofed IP packets. The Unicast Reverse Path Forwarding (Unicast RPF) feature helps to mitigate problems that are caused by spoofed IP source addresses. It is available on Cisco routers and firewalls. For further details, please refer to: http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr /fsecur_c/fothersf/scfrpf.htm By enabling Unicast Reverse Path Forwarding (uRPF), all spoofed packets will be dropped at the first device. To enable uRPF, use the following commands. router(config)# ip cef router(config)# interface router(config-if)# ip verify unicast reverse-path 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 website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.0 (SunOS) iD8DBQFDpzDwEHa/Ybuq8nARAutnAJ9cFhTKVv8C5K4QcIWJiMYomuLnWgCeJU8Q Xd773GAB2i9O6ad8ZQ1+F9o= =toA7 -----END PGP SIGNATURE-----
