Vulnerability Note VU#727780

Cisco VPN 3000 Concentrator may allow access to internal hosts when IPsec over TCP is enabled

Original Release date: 23 Jun 2003 | Last revised: 23 Jun 2003


A vulnerability in some Cisco Virtual Private Network (VPN) products could allow a remote attacker to access systems that should not be accessible.


The Cisco VPN 3000 Series Concentrators and the Cisco VPN 3002 Hardware Clients are Virtual Private Network (VPN) platforms designed to provide secure remote network access. Some models of these devices contain a vulnerability by which a TCP port selected for forwarding IPsec over TCP traffic is forwarded to all systems on the protected network and not just the systems using IPsec. This may allow an attacker to access services that should not be accessible from the public network without authentication of any sort.


A remote attacker may be able to gain unintended access to the private network on the affected device. Attackers could leverage this access to exploit additional, unrelated vulnerabilities in services that use the same TCP port as that used to tunnel the IPsec traffic.


Cisco Systems Inc. has released software patches and workaround information for this vulnerability. Please see the vendor information section of this document for more details.


Cisco recommends adding rules to the filter for the private interface that restrict outgoing traffic on ports configured for use by IPsec over TCP on the VPN concentrator. This would not stop the traffic from the public network reaching the VPN 3000 concentrator itself but would prevent the traffic from reaching the servers on the private network.

If patches cannot be applied, sites may wish to select a less-commonly used TCP port for the IPsec tunnel to limit the services that might be available to attack over the tunnel.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
Cisco Systems Inc.Affected-08 May 2003
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



Thanks to Cisco Systems Product Security Incident Response Team for reporting this vulnerability.

This document was written by Chad R Dougherty.

Other Information

  • CVE IDs: CAN-2003-0258
  • Date Public: 07 May 2003
  • Date First Published: 23 Jun 2003
  • Date Last Updated: 23 Jun 2003
  • Severity Metric: 23.73
  • Document Revision: 10


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