Advisory ID: cisco-sa-20050330-vpn3k
For Public Release 2005 April 6 16:00 UTC (GMT)
Vulnerability Scoring Details
Software Versions and Fixes
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: Final
Cisco Security Procedures
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 advisory is available at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20050330-vpn3k
This section provides details on affected 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.
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.
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.
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.
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.
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:
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.
Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html , or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml .
Do not contact email@example.com or firstname.lastname@example.org for software upgrades
The effectiveness of any workaround or fix 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 or fix is the most appropriate for use in the intended network before it is deployed.
Customers who purchase direct from Cisco but do not hold a Cisco service contract, and customers who purchase through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain software patches and bug fixes 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: email@example.com
Customers should have the product serial number available and be prepared to provide the URL of this notice as evidence of entitlement to a software patch or bug fix. Customers without service contracts should request a software patch or bug fix through the TAC.
Refer to http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including localized telephone numbers, and instructions and e-mail addresses for use in various languages.
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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