Cisco Security Advisory: Vulnerability In Crypto Library

Contents

Summary
Affected Products
Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: Interim
Distribution
Revision History
Cisco Security Procedures

Vulnerable Products

Affected protocols in Cisco IOS

To determine the software running on a Cisco IOS product, log in to the device and issue the show version command to display the system banner. Cisco IOS software will identify itself as "Internetwork Operating System Software" or simply "IOS." On the next line of output, the image name will be displayed between parentheses, followed by "Version" and the Cisco IOS release name. Other Cisco devices will not have the show version command, or will give different output.

Only Cisco IOS images that contain the Crypto Feature Set are vulnerable. Customers who are not running an IOS image with crypto support are not exposed to this vulnerability.

Cisco IOS feature set naming indicates that IOS images with crypto support have 'K8' or 'K9' in the feature designator field.

The following example shows output from a device running an IOS image with crypto support:

Router>show version
Cisco IOS Software, 7200 Software (C7200-IK9S-M), Version 12.3(14)T1, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2005 by Cisco Systems, Inc.
Compiled Thu 31-Mar-05 08:04 by yiyan

Since the feature set designator (IK9S) contains 'K9', it can be determine that this feature set contains crypto support.

Additional information about Cisco IOS release naming is available at the following link: http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/ products_white_paper09186a008018305e.shtml.

You are affected by this vulnerability if you are running one of the vulnerable IOS software releases and have, at least one, of the following protocols or features enabled:

• Internet Security Association and Key Management Protocol (ISAKMP)
  
• In some IOS releases the Secure Socket Layer (SSL) may also be affected
  
• Threat Information Distribution Protocol (TIDP)
  
• Cisco IOS SIP Gateway Signaling Support Over TLS (SIP-TLS)
  
• Extensible Authentication Protocol-Transport Layer Security (EAP-TLS)
  

As some other protocols may use affected crypto library the most accurate way to determine if your IOS release is vulnerable is to consult fixed IOS releases table.

Internet Security Association and Key Management Protocol (ISAKMP)

In order for an IOS device to be vulnerable, crypto map must be explicitly configured and applied to an interface. All authentication methods (i.e., pre-shared key, certificates) are affected.

To determine if your device has ISAKMP enabled, enter the command show crypto isakmp policy. Below is an example of a device that has ISAKMP enabled.

Router#show crypto isakmp policy

Global IKE policy
Protection suite of priority 1
<more output>

If your output is like in the following example then you do not have IKE enabled on your device.

Router#show crypto isakmp policy
ISAKMP is turned off

In Cisco IOS two features rely on ISAKMP - IPSec and Group Domain of Interpretation (GDOI). Presence of either of these features is detected by the previous example.

Prior to IOS version 12.3(2)T, IKE was enabled by default, with no crypto configuration needed for the IOS device to process IKE messages.

12.2SXD versions of Cisco IOS have IKE enabled by default. To ensure that IKE processing is disabled, enter the global configuration command no crypto isakmp enable.

As of IOS version 12.3(2)T (which includes all 12.4-based versions), crypto configuration is required to enable IKE message processing.

Secure Socket Layer (SSL)

In some Cisco IOS software releases the vulnerable library is used to process elements of SSL functionalities. SSL is used to protect several application layer protocols like Hyper Text Transfer Protocol over SSL (HTTPS).

HTTPS is not the only protocol that may use SSL but it is the most commonly known. In order to determine if your device has HTTPS configured enter the command show running | include secure. Below is an example of a device that has HTTPS enabled.

router#show running | include secure-server
ip http secure-server

Threat Information Distribution Protocol (TIDP)

To determine if your device has TDIP enabled, enter the command show running-config | include parameter-map. Below is an example of a device that has TDIP enabled.

router#show running | include parameter-map
parameter-map type tms TMS_PAR

Cisco IOS SIP Gateway Signaling Support Over TLS (SIP-TLS)

To determine if your device has SIP-TLS enabled, enter the command show running-config | include crypto signaling. Below is an example of a device that has SIP-TLS enabled.

router#show running | include crypto signaling
crypto signaling default trustpoint user1

Extensible Authentication Protocol-Transport Layer Security (EAP-TLS)

To determine if your device has EAP-TLS enabled, enter the command show running-config | include method. Below is an example of a device that has EAP-TLS enabled.

Router#show running | include method
method tls

Products Confirmed Not Vulnerable

ASN.1 is defined by ITU-T (International Telecommunication Union - Telecommunication Standardization Sector) standards and it describes, among other things, data structures for encoding values. The vulnerability addressed by this advisory is related to the implementation of parsing certain data structures and is not a vulnerability in the standard itself.

Protocols that use ASN.1 (e.g., voice over IP, Simple Network Management Protocol and others), but do not rely on the vulnerable crypto library, are not affected. This advisory only addresses an implementation issue in a particular crypto library from a single vendor.

This vulnerability is present in the following Cisco products:

• Cisco IOS, documented as Cisco bug ID CSCsd85587 ( registered customers only)
  
• Cisco IOS XR, documented as Cisco bug ID CSCsg41084 ( registered customers only)
  
• Cisco PIX and ASA Security Appliances, documented as Cisco bug ID CSCse91999 ( registered customers only)
  
• Cisco Firewall Services Module (FWSM), documented as Cisco bug ID CSCsi97695 ( registered customers only)
  
• Cisco Unified CallManager, documented as Cisco bug ID CSCsg44348 ( registered customers only)
  

Vulnerability Scoring Details

Cisco is providing scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS).

Cisco will provide a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco PSIRT will set the bias in all cases to normal. Customers are encouraged to apply the bias parameter when determining the environmental impact of a particular vulnerability.

CVSS is a standards based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided an FAQ to answer additional questions regarding CVSS at http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html.

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at http://intellishield.cisco.com/security/alertmanager/cvss.

Successful exploitation of the vulnerability listed in this advisory may result in the crash of a vulnerable device. Repeated exploitation can result in a sustained DoS attack.

In the case of IOS XR, successful exploitation will not crash the whole device but only the affected service. Successful repeated exploitation of this vulnerability may lead to a sustained Denial-of-Service (DoS) of affected services but not the whole device.

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.

Each row of the Cisco IOS software table (below) describes a release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (the "First Fixed Release") and the anticipated date of availability for each are listed in the "Rebuild" and "Maintenance" columns. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than or equal to the First Fixed Release label).

For more information on the terms "Rebuild" and "Maintenance," consult the following URL: http://www.cisco.com/warp/public/620/1.html

Cisco IOS

Fixed Cisco IOS software releases are listed in the table below.

Cisco IOS XR

The following table lists fixed Cisco IOS XR software.

IOS XR Package Installation Envelopes (PIE) can be downloaded from File Exchange at: https://upload.cisco.com/cgi-bin/swc/fileexg/main.cgi?CONTYPES=IOS-XR ( registered customers only) . Installation instructions are included in the accompanying .txt files.

Cisco PIX and ASA Security Appliance

This vulnerability is fixed in the following 7.x software releases: 7.0(6.7), 7.1(2.27), 7.2(1.22), 7.2(2). All 8.x software releases do contain the fixed library and are not affected. No 6.x software releases are affected by this vulnerability.

Cisco Firewall Service Module (FWSM)

This vulnerability is fixed in the following software releases:

• 3.1(6) maintenance release, expected in 2007-June
  

Cisco Unified CallManager

This vulnerability is fixed in the following software releases.

• 4.0(x) releases are vulnerable but no fix will be provided. Customers are advised to upgrade to the fixed 4.1 or 4.2 software.
  
• 4.1(3)sr.5 expected in 2007-May-24
  
• 4.2(3)sr.2 expected in 2007-May
  
• 4.3(1)sr.1 expected 2007-Jun
  
• 5.0(4) - no fixed software planned, users should upgrade to 5.1(2)
  
• 5.1(1) - no fixed software planned, users should upgrade to 5.1(2)
  
• 5.1(2)
  

The only way to prevent a device being susceptible to the listed vulnerabilities is to disable the affected service(s). However, if regular maintenance and operation of the device relies on these services then there is no workaround.

It is possible to mitigate these vulnerabilities by preventing unauthorized hosts to access the affected devices. Additional mitigations that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory: http://www.cisco.com/warp/public/707/cisco-amb-20070522-crypto.shtml

Control Plane Policing (CoPP)

Control Plane Policing: IOS software versions that support Control Plane Policing (CoPP) can be configured to help protect the device from attacks that target the management and control planes. CoPP is available in Cisco IOS release trains 12.0S, 12.2SX, 12.2S, 12.3T, 12.4, and 12.4T.

In the CoPP example below, the ACL entries that match the exploit packets with the permit action will be discarded by the policy-map drop function, while packets that match a deny action (not shown) are not affected by the policy-map drop function.

!-- Include deny statements up front for any protocols/ports/IP addresses that
!-- should not be impacted by CoPP
!-- Include permit statements for the protocols/ports that will be governed by CoPP
!-- port 443 - HTTPS
access-list 100 permit tcp any any eq 443
!-- port 500 - IKE
access-list 100 permit udp any any eq 500
!-- port 848 - GDOI
access-list 100 permit tcp any any eq 848
!-- port 5060 - SIP-TLS
access-list 100 permit tcp any any eq 5060
!-- port 5354 - TIDP
access-list 100 permit tcp any any eq 5354

!-- Permit (Police or Drop)/Deny (Allow) all other Layer3 and Layer4            
!-- traffic in accordance with existing security policies and                   
!-- configurations for traffic that is authorized to be sent                    
!-- to infrastructure devices.                                                  
!                                                                               
!-- Create a Class-Map for traffic to be policed by                             
!-- the CoPP feature.                                                           
!                                                                               
class-map match-all Drop-Known-Undesirable                                       
 match access-group 100                                                          

!                                                                               
!-- Create a Policy-Map that will be applied to the                             
!-- Control-Plane of the device.                                                
!                                                                               
policy-map CoPP-Input-Policy                                                    
 class Drop-Known-Undesirable                                                    
  drop                                                                            

!-- Apply the Policy-Map to the Control-Plane of the                            
!-- device.                                                                     
!                                                                               
control-plane                                                                   
 service-policy input CoPP-Input-Policy

Please note that in the 12.0S, 12.2S, and 12.2SX Cisco IOS trains, the policy-map syntax is different:

policy-map CoPP-Input-Policy
 class Drop-Known-Undesirable
 police 32000 1500 1500 conform-action drop exceed-action drop

NOTE: In the above CoPP example, the ACL entries with the "permit" action that match the exploit packets result in the discarding of those packets by the policy-map drop function, while packets that match the "deny" action are not affected by the policy-map drop function.

Additional information on the configuration and use of the CoPP feature can be found at http://www.cisco.com/en/US/products/ps6642/products_white_paper0900aecd804fa16a.shtml and http://www.cisco.com/en/US/products/sw/iosswrel/ps1838/products_feature_guide09186a008052446b.html .

Access Control List (ACL)

Access control lists can be used to help mitigate attacks that may try to exploit these vulnerabilities. This is done in a way that only packets from the legitimate sources are allowed to reach the device and all others are dropped.

access-list 101 permit tcp host <legitimate_host_IP_address> host <router_IP_address> eq 443
access-list 101 permit udp host <legitimate_host_IP_address> host <router_IP_address> eq 500
access-list 101 permit tcp host <legitimate_host_IP_address> host <router_IP_address> eq 506
access-list 101 permit tcp host <legitimate_host_IP_address> host <router_IP_address> eq 4848
access-list 101 permit tcp host <legitimate_host_IP_address> host <router_IP_address> eq 5060
access-list 101 permit tcp host <legitimate_host_IP_address> host <router_IP_address> eq 5354
access-list 101 deny tcp any any eq 443
access-list 101 deny udp any any eq 500
access-list 101 deny tcp any any eq 506
access-list 101 deny udp any any eq 4848                                      
access-list 101 deny tcp any any eq 5060
access-list 101 deny tcp any any eq 5354

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 http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set forth at Cisco.com Downloads athttp://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com" 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 http://www.cisco.com.

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@cisco.com
  

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 http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including special 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 by Cisco during internal testing.

This advisory is posted on Cisco's worldwide website at http://www.cisco.com/warp/public/707/cisco-sa-20070522-crypto.shtml.

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@cisco.com
  
• first-teams@first.org
  
• bugtraq@securityfocus.com
  
• vulnwatch@vulnwatch.org
  
• cisco@spot.colorado.edu
  
• cisco-nsp@puck.nether.net
  
• full-disclosure@lists.grok.org.uk
  
• comp.dcom.sys.cisco@newsgate.cisco.com
  

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.

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 http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.