Cisco Security Advisory
Cisco VPN 3000 Concentrator Vulnerable to Crafted HTTP Attack
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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 crafted packets to a concentrator which may cause the device to halt and/or drop user connections. The power must then be reset on the device to recover.
Cisco has made free software available to address this vulnerability for affected customers. There are workarounds available to mitigate this vulnerability as well.
This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20060126-vpn.
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This section provides details on affected products.
Vulnerable Products
Cisco VPN 3000 series concentrators 3005, 3015, 3020, 3030 and the 3080 are affected by this vulnerability.
Products Confirmed Not Vulnerable
The following products are confirmed not vulnerable:
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Cisco VPN 3002 Hardware Client
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Cisco IPSec VPN Services Module (VPNSM)
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Cisco WebVPN Service Module (WebVPN)
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Cisco VPN 5000 Concentrators
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Cisco PIX Firewalls
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Cisco Adaptive Security Appliance (ASA)
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Any Cisco device that runs Cisco's Internetwork Operating System
(IOS)
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Any Cisco device that runs Cisco's Catalyst Operating System
(CatOS)
No other Cisco products are currently known to contain these vulnerabilities.
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Cisco VPN 3002 Hardware Client
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Hypertext Transfer Protocol (HTTP) is a set of rules for exchanging files (text, graphic images, sound, video, and other multimedia files) on the World Wide Web. HTTP is an application protocol for which the default TCP port is 80. Due to this vulnerability, a malicious user may send crafted HTTP packets which may result in a reload of the affected device and/or user connections being dropped.
The affected products are only vulnerable if they have the HTTP service enabled. By default, HTTP is enabled on VPN 3000 devices, however it may be manually disabled. Affected devices are not vulnerable to transit traffic, only traffic that is destined to them may exploit this vulnerability.
To check if the HTTP service is enabled, please do the following:
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Check the configuration on the device to verify the status of the
HTTP service.
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Try to connect to the device using a standard web browser that
supports using a URL similar to
http://ip_address_of_device/.
This vulnerability is documented in the Cisco Bug Toolkit as Bug ID CSCsb77324 ( registered customers only) and CSCsd26340 ( registered customers only) .
Vulnerable versions of Cisco VPN 3000 do not manage certain TCP connections aggressively, which may leave the concentrator vulnerable to a denial of service attack.
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CSCsb77324 - A malicious user may be able to send a
small series of crafted HTTP packets to a concentrator which will cause the
device to halt and drop user connections. The power must then be reset on the
device to recover.
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CSCsd26340 - The concentrator does not manage TCP
connections to port 80 aggressively enough, leading to a scenario where memory
and other resources are consumed with open connections. In specific scenarios,
the concentrator will stall and drop user connections. The device must then be
restarted via console access or by resetting power on the device.
Alternatively, the device will recover automatically within about 20 minutes,
however during this time the device is unavailable except via console
access.
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Check the configuration on the device to verify the status of the
HTTP service.
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This section provides workarounds for this vulnerability.
Disable HTTP
Disabling HTTP will effectively mitigate this vulnerability.
With HTTP disabled, the concentrator can be configured to use HTTPS (HyperText Transfer Protocol Secure) for both concentrator management and WebVPN connectivity if WebVPN connectivity is configured on the concentrator.
To implement this workaround, first enable HTTPS, then disable HTTP.
If WebVPN is used, it is important to also disable any HTTP proxies that may be configured (HTTPS is always enabled for WebVPN if WebVPN is enabled).
For details on how to enable HTTPS management of the concentrator, please reference:
For details on how to disable HTTP management of the concentrator, please reference:
For details on how to disable WebVPN HTTP proxies, please reference:
Infrastructure ACLs
HTTP to the VPN3000 could be blocked as part of an Infrastructure ACL on screening routers, switches and firewalls controlling all access to the trusted network. Infrastructure 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 "Protecting Your Core: Infrastructure Protection Access Control Lists" presents guidelines and recommended deployment techniques:
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801a1a55.shtml
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When considering software upgrades, also consult http://www.cisco.com/go/psirt 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") or your contracted maintenance provider for assistance.
Vulnerability
Affected Major Release
First Fixed Release
HTTP DoS Attack (CSCsb77324)
4.0.X or earlier
Not Vulnerable
4.1.X
Not Vulnerable
4.7.2.
4.7.2.B
TCP Attack (CSCsd26340)
4.0.X or earlier
Not Vulnerable
4.1.X
4.1.7.L
4.7.X
4.7.2.F
Cisco VPN 3000 series users can upgrade to version 4.1.7.L or 4.7.2.F or later software to resolve both vulnerabilities.
Cisco VPN 3000 software is available for download at http://www.cisco.com/pcgi-bin/tablebuild.pl/vpn3000-3des.
When considering software upgrades, also consult http://www.cisco.com/go/psirt 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) or your contracted maintenance provider for assistance.
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The Cisco PSIRT is not aware of any malicious use of the vulnerability described in this advisory.
These issues were reported to Cisco by Eldon Sprickerhoff from Esentire and discussed at the Shmoocon security conference on January 14th, 2006.
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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 Less
Revision 2.1
14-August-2007
Fixed link.
Revision 2.0
26-April-2006
Updated to include DDTS CSCsd26340.
Revision 1.1
01-February-2006
- Corrected impact of successful exploitation of this vulnerability - device halts instead of reloading.
- Fixed typo in name of security conference where this vulnerability was discussed.
Revision 1.0
26-January-2006
Initial public release.
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