Cisco VPN 3000 Concentrator Vulnerable to Crafted HTTP Attack

Risk: Medium
Local: Yes
Remote: Yes

CVSS Base Score: 7.8/10
Impact Subscore: 6.9/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: None
Integrity impact: None
Availability impact: Complete

UPDATE : At present, the only way to defend against this attack is by disabling inbound tcp/80. Further details are available at: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Cisco Security Advisory: Cisco VPN 3000 Concentrator Vulnerable to Crafted HTTP Attack Advisory ID: cisco-sa-20060126-vpn Revision 1.0 For Public Release 2006 January 26 1700 UTC (GMT) +-------------------------------------------------------------------- Contents ======== Summary Affected Products Details Impact Software Versions and Fixes Workarounds Obtaining Fixed Software Exploitation and Public Announcements Status of This Notice: FINAL Distribution Revision History Cisco Security Procedures +-------------------------------------------------------------------- Summary ======= 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 HTTP (Hypertext Transfer Protocol) packet to the concentrators which may cause the device to reload and drop user connections. Repeated exploitation of this vulnerability will create a sustained DoS (denial of service). 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 Affected Products ================= Vulnerable Products +------------------ Cisco VPN 3000 series concentrators running software 4.7.0 through 4.7.2.A are affected by this vulnerability. This includes version 4.7REL. Software versions prior to 4.7.x are not vulnerable. This series includes models 3005, 3015, 3020, 3030, 3060, and the 3080. Products Confirmed Not Vulnerable +-------------------------------- The following products are confirmed not vulnerable: * Cisco VPN 3002 Hardware Client * Cisco IPSec VPN Services Module (VPNSM) * Cisco VPN 5000 Concentrators * Cisco PIX Firewalls * Cisco Adaptive Security Appliance (ASA) * 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. Details ======= 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: 1. Check the configuration on the device to verify the status of the HTTP service. 2. 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. Impact ====== Successful exploitation of this vulnerability may result in a reload of the affected device and user connections being dropped. Repeated exploitation of this vulnerability could result in a sustained Denial of Service. Software Versions and Fixes =========================== Cisco VPN 3000 series software version 4.7.2.B and later is not vulnerable. Cisco VPN 3000 series users can upgrade to version 4.7.2.B or later software to resolve this vulnerability. Cisco VPN 3000 software is available for download at When considering software upgrades, also consult 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. Workarounds =========== 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 proxys 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: products_configuration_guide_chapter09186a00803ee1e4.html#wp1309312 For details on how to disable HTTP management of the concentrator, please reference: products_configuration_guide_chapter09186a00803ee11f.html#wp999607 For details on how to disable WebVPN HTTP proxies please see: products_configuration_guide_chapter09186a00803ee1e4.html#wp1400335 Infrastructure ACLs +------------------ HTTP to the VPN3000 could be blocked as part of a 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: technologies_white_paper09186a00801a1a55.shtml Obtaining Fixed Software ======================== Cisco has made free software available to address this vulnerability for affected customers. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment. 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 or as otherwise set forth at Downloads at Do not contact either "psirt (at) cisco (dot) com [email concealed]" or "security-alert (at) cisco (dot) com [email concealed]" for software upgrades. Customers with Service Contracts +------------------------------- Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's worldwide website at Customers using Third-party Support Organizations +------------------------------------------------ Customers whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for guidance and assistance with the appropriate course of action in regards to this advisory. 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 without Service Contracts +---------------------------------- Customers who purchase direct from Cisco but who do not hold a Cisco service contract and customers who purchase through third-party vendors but are unsuccessful at obtaining fixed software through their point of sale should get their upgrades 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: tac (at) cisco (dot) com [email concealed] Have your product serial number available and give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC. Refer to for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages. Exploitation and Public Announcements ===================================== The Cisco PSIRT is not aware of any malicious use of the vulnerability described in this advisory. This issue was discussed at the Schmoocon security conference on January 12th, 2006. Status of This Notice: FINAL ============================ THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME. A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors. Distribution ============ This advisory is posted on Cisco's worldwide website at In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients. * cust-security-announce (at) cisco (dot) com [email concealed] * first-teams (at) first (dot) org [email concealed] * bugtraq (at) securityfocus (dot) com [email concealed] * vulnwatch (at) vulnwatch (dot) org [email concealed] * cisco (at) spot.colorado (dot) edu [email concealed] * cisco-nsp (at) puck.nether (dot) net [email concealed] * full-disclosure (at) (dot) uk [email concealed] * (at) (dot) com [email concealed] Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates. Revision History ================ +---------------------------------------+ | Revision | | Initial | | 1.0 | 26-January-2006 | public | | | | release. | +---------------------------------------+ Cisco Security Procedures ========================= Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at products_security_vulnerability_policy.html This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at +-------------------------------------------------------------------- -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.0 (SunOS) iD8DBQFD2QHXezGozzK2tZARAubKAKDpiLtQLI2ggmy3cWC5sS0qkk8lgACg/r0k iBL76nBznqI2fEa0q2tEPSg= =bFnq -----END PGP SIGNATURE-----

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