A vulnerability in Cisco IOS Easy VPN Server may allow unauthorized users to complete XAUTH authentication and potentially access private network resources.
Easy VPN Server
Cisco IOS Easy VPN Server allows an IOS device to function as a VPN concentrator, providing authentication and encrypted access to network resources. Easy VPN Server was introduced in IOS 12.2(8)T.
IPSec is a set of standards developed by the IETF that provides data confidentiality, integrity, and authentication at the IP layer. IPSec is used by applications such as Virtual Private Networks (VPNs).
Internet Key Exchange (IKE)
IKE (RFC2409) is a protocol that negotiates and provides authenticated keying material for security associations (SAs) in a protected manner. IKE is accomplished by using a combination of ISAKMP (RFC2408) and other protocols. ISAKMP provides a framework for internet key management. The IKE negotiation process consists of two phases. Phase 1 establishes an ISAKMP SA. Phase 2 is used to create SAs for other security protocols.
Extended Authentication (XAUTH) is an extension to IKE. It is defined in the expired document
draft-ietf-ipsec-isakmp-xauth-06.txt. XAUTH allows IKE to use existing unidirectional authentication mechanisms after the Phase 1 SA has been established. XAUTH has been rejected by the IETF due to security flaws.
When certain packets are sent to a Cisco Easy VPN server on port
500/udp, XAUTH authentication may be completed. This may allow access to network resources. Because XAUTH authentication takes place after the IKE Phase 1 negotiation, an attacker must know the shared group key to successfully perform this attack.
A remote attacker may be able to gain unintended access to the private network on the affected device.
Apply a patch or upgrade
Do not use XAUTH
XAUTH contains several security flaws and has been rejected by the IETF.
Use strong group passwords
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Updated: April 07, 2005
We have not received a statement from the vendor.
The vendor has not provided us with any further information regarding this vulnerability.
Please see the Cisco Security Advisory.
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This vulnerability was reported by the Cisco Systems Product Security Incident Response Team (PSIRT).
This document was written by Will Dormann.
CVE IDs: | CVE-2005-1057
Severity Metric: | 1.89
Date Public: | 2005-04-06
Date First Published: | 2005-06-08
Date Last Updated: | 2005-06-08 18:53 UTC
Document Revision: | 20