Cisco Security Advisory-
The Cisco VPN 3000 series concentrators are a family of purpose-built, remote access Virtual Private Network (VPN) platforms for data encryption and authentication.
A malicious user may be able to send a crafted attack via SSL (Secure Sockets Layer) to the concentrators which may cause the device to reload, and/or drop user connections.
Repeated exploitation will create a sustained DoS (denial of service).
Workarounds are available to mitigate this vulnerability.
Cisco has made free software available to address this vulnerability for all affected customers.
This vulnerability is documented in the Cisco Bug Toolkit as Bug ID CSCeg11424 ( registered customers only)
This advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050330-vpn3k
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This section provides details on affected products.
Vulnerable Products
Cisco VPN 3000 series concentrators running software 4.1.7.A and earlier are affected by this vulnerability.
This series includes models 3005, 3015, 3020, 3030, 3060, 3080 and the Cisco VPN 3002 Hardware Client.
Products Confirmed Not Vulnerable
The following products are confirmed not vulnerable:
- Cisco IPSec VPN Services Module (VPNSM)
- Cisco VPN 5000 Concentrators
- Cisco PIX Firewalls
- Any Cisco device that runs Cisco's Internetwork Operating System (IOS)
- Any Cisco device that runs Cisco's Catalyst Operating System (CatOS)
No other Cisco products are currently known to contain this vulnerability.
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Secure Sockets Layer (SSL) is a protocol used to encrypt the data transferred over a TCP session. SSL in Cisco products is mainly used by the HyperText Transfer Protocol Secure (HTTPS) web service for which the default TCP port is 443. Due to this vulnerability, a malicious user may send crafted HTTPS packets which may result in a reload of the affected device or and/or user connections being dropped.
The affected products are only vulnerable if they have the HTTPS service enabled and the access to the service is not limited to trusted hosts or network management workstations. By default, HTTPS is not enabled on VPN 3000 devices, and must be manually enabled. Affected devices are not vulnerable to transit traffic, only traffic that is destined to them may exploit this vulnerability.
To check if the HTTPS service is enabled, one can do the following:
- Check the configuration on the device to verify the status of the HTTPS service.
- Try to connect to the device using a standard web browser that supports SSL using a URL similar to https://ip_address_of_device/.
No authentication is required to exploit this vulnerability.
This vulnerability is documented in the Cisco Bug Toolkit as Bug ID CSCeg11424 ( registered customers only)
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Disable HTTPS
Disabling HTTPS will effectively mitigate this vulnerability, provided the concentrator is used only for IPSEC, PPTP or L2TP over IPsec VPN connections. If the concentrator is configured for WebVPN connectivity, disabling HTTPS will also render WebVPN inoperable.
For details on how to disable HTTPS, please reference www.cisco.com/en/US/docs/security/vpn3000/vpn3000_47/configuration/guide/tunnel.html#wp1309633.
Transit ACLs
SSL to the VPN3000 could be blocked as part of a Transit ACL on screening routers, switches and firewalls controlling all access to the trusted network. Transit ACLs are considered a network security best practice and should be considered as a long-term addition to good network security, as well as a workaround for this specific vulnerability. The white paper entitled "Transit Access Control Lists: Filtering at Your Edge" presents guidelines and recommended deployment techniques for transit ACLs:
http://www.cisco.com/warp/public/707/tacl.html.
The effectiveness of any workaround is dependent on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround is the most appropriate for use in the intended network before it is deployed.
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Cisco VPN 3000 series users can upgrade to version 4.1.7.B or later software to resolve this vulnerability.
When considering software upgrades, please also consult http://www.cisco.com/warp/public/707/advisory.html and any subsequent advisories to determine exposure and a complete upgrade solution.
In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center ("TAC") for assistance.
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The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.
This vulnerability was discovered during internal Cisco security review.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessRevision 1.1
2007-August-14
Fixed Link.
Revision 1.0
2005-April-06
Initial Release.
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