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Cisco Security Advisory

Vulnerability in Cisco IOS While Processing SSL Packet

Advisory ID: cisco-sa-20080924-ssl

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ssl

Revision 1.1

For Public Release 2008 September 24 16:00  UTC (GMT)

Related Resources:

View related Alert

Summary

A Cisco IOS device may crash while processing an SSL packet. This can happen during the termination of an SSL-based session. The offending packet is not malformed and is normally received as part of the packet exchange.

Cisco has released free software updates that address this vulnerability. Aside from disabling affected services, there are no available workarounds to mitigate an exploit of this vulnerability.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ssl.

Note: The September 24, 2008 IOS Advisory bundled publication includes twelve Security Advisories. Eleven of the advisories address vulnerabilities in Cisco's IOS software, and one advisory addresses vulnerabilities in Cisco Unified Communications Manager. Each Advisory lists the releases that correct the vulnerability described in the Advisory.

Individual publication links are listed below:

Affected Products

Vulnerable Products

Devices running Cisco IOS and using SSL-based services are susceptible to this vulnerability. Some of the services that utilize SSL are:

  • HTTP server supporting SSL encryption (HTTPS)
    The following example shows a device that has the standard Cisco IOS HTTP server disabled, but the SSL-enabled Cisco IOS HTTP server enabled:
    Router#show running-config | include ip http
    no ip http server
    ip http secure-server
    Router#
  • SSL Virtual Private Network (SSL VPN) also known as AnyConnect VPN
    The following example shows a device that has the SSL VPN feature enabled:
    Router#show running-config | include webvpn
    webvpn enable
    webvpn
    Router#
  • Open Settlement Protocol (OSP) for Packet Telephony feature
    The following example shows a device that has the OSP feature enabled and uses HTTPS protocol that is vulnerable:
    Router#show running-config | include url
    url https://<host_ip_address>:443/
    Router#

The Cisco IOS Bug Toolkit may not accurately reflect the affected releases for this advisory. The affected releases are as follows:

  • 12.4(16)MR, 12.4(16)MR1, 12.4(16)MR2
  • 12.4(17)

To determine the version of the Cisco IOS software running on a Cisco 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 IOS release name. Other Cisco devices will not have the show version command or will give different output.

Router#show version
Cisco IOS Software, 1841 Software (C1841-ADVSECURITYK9-M), Version 12.4(15)T2, 
   RELEASE SOFTWARE (fc7) 
Technical Support: http://www.cisco.com/techsupport 
Copyright (c) 1986-2008 by Cisco Systems, Inc. 
Compiled Thu 17-Jan-08 23:12 by prod_rel_team

Additional information about Cisco IOS software release naming is available at the following link: http://www.cisco.com/warp/public/620/1.html.

Products Confirmed Not Vulnerable

No other Cisco products and Cisco IOS releases are currently known to be affected by this vulnerability.

Details

This vulnerability is triggered during the termination of an SSL session. Possession of valid credentials such as a username, password or a certificate is not required. SSL protocol uses TCP as a transport protocol. The requirement of the complete TCP 3-way handshake reduces the probability that this vulnerability will be exploited through the use of spoofed IP addresses.

A device running vulnerable Cisco IOS Software with SSL-based service configured will crash while terminating an SSL session.

This vulnerability is documented in Cisco Bug ID CSCsj85065 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2008-3798.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.

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

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

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.

Router reload while processing SSL packets

Calculate the environmental score of CSCsj85065

CVSS Base Score - 7.8

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

None

None

Complete

CVSS Temporal Score - 6.4

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed

Impact

A successful exploit of this vulnerability may cause a crash of the affected device. Repeated exploitation may result in a sustained denial of service condition.

Software Versions and Fixes

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) names a Cisco IOS release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (along with the anticipated date of availability for each, if applicable) are listed in the "First Fixed Release" column of the table. The "Recommended Release" column indicates the releases which have fixes for all the published vulnerabilities at the time of this Advisory. 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. Cisco recommends upgrading to a release equal to or later than the release in the "Recommended Releases" column of the table.

Major Release

Availability of Repaired Releases

Affected 12.0-Based Releases

First Fixed Release

Recommended Release

There are no affected 12.0 based releases

Affected 12.1-Based Releases

First Fixed Release

Recommended Release

There are no affected 12.1 based releases

Affected 12.2-Based Releases

First Fixed Release

Recommended Release

There are no affected 12.2 based releases

Affected 12.3-Based Releases

First Fixed Release

Recommended Release

There are no affected 12.3 based releases

Affected 12.4-Based Releases

First Fixed Release

Recommended Release

12.4

12.4(17a)

12.4(18)

12.4(18c)

12.4JA

Not Vulnerable

 

12.4JK

Not Vulnerable

 

12.4JL

Not Vulnerable

 

12.4JMA

Not Vulnerable

 

12.4JMB

Not Vulnerable

 

12.4JMC

Not Vulnerable

 

12.4JX

Not Vulnerable

 

12.4MD

Not Vulnerable

 

12.4MR

12.4(19)MR

12.4(19)MR

12.4SW

Not Vulnerable

 

12.4T

Not Vulnerable

 

12.4XA

Not Vulnerable

 

12.4XB

Not Vulnerable

 

12.4XC

Not Vulnerable

 

12.4XD

Not Vulnerable

 

12.4XE

Not Vulnerable

 

12.4XF

Not Vulnerable

 

12.4XG

Not Vulnerable

 

12.4XJ

Not Vulnerable

 

12.4XK

Not Vulnerable

 

12.4XL

Not Vulnerable

 

12.4XM

Not Vulnerable

 

12.4XN

Not Vulnerable

 

12.4XP

Not Vulnerable

 

12.4XQ

Not Vulnerable

 

12.4XT

Not Vulnerable

 

12.4XV

Not Vulnerable

 

12.4XW

Not Vulnerable

 

12.4XY

Not Vulnerable

 

12.4XZ

Not Vulnerable

 


Workarounds

To prevent an exploit of a vulnerable device, SSL-based services need to be disabled. However, if regular maintenance and operation of the device relies on this service, there is no workaround.

The following command will disable the vulnerable HTTPS service:

Router(config)#no ip http secure-server

The following command will disable the vulnerable SSL VPN service:

Router(config)#no webvpn enable

The following command will disable the vulnerable OSP service:

Router(config)#no settlement <n>

Another option is to revert to HTTP protocol instead using HTTPS. The downside of this workaround is that the settlement information will be sent over the network unprotected.

It is possible to mitigate this vulnerability by preventing unauthorized hosts from accessing affected devices.

Control Plane Policing (CoPP)

Cisco 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 following CoPP example, the ACL entries that match the exploit packets with the permit action will be discarded by the policy-map drop function, whereas 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 CoPPaccess-list 100 permit tcp any any eq 443
!-- 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-SSL-class match access-group 100

!
!-- Create a Policy-Map that will be applied to the
!-- Control-Plane of the device.
!

policy-map drop-SSL-policy class drop-SSL-class   drop   

!-- Apply the Policy-Map to the Control-Plane of the
!-- device.
!

control-plane service-policy input drop-SSL-policy

Note: In the preceding CoPP example, the ACL entries with the permit action that match the exploit packets will result in the discarding of those packets by the policy-map drop function, whereas 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 is available at the following links: http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6586/ps6642/prod_white_paper0900aecd804fa16a.html and http://www.cisco.com/en/US/docs/ios/12_3t/12_3t4/feature/guide/gtrtlimt.html.

Access Control List (ACL)

An Access Control List (ACL) can be used to help mitigate attacks that target this vulnerability. ACLs can specify that only packets from legitimate sources are permitted to reach a device, and all others are to be dropped. The following example shows how to allow legitimate SSL sessions from trusted sources and deny all other SSL sessions:

access-list 101 permit tcp host <legitimate_host_IP_address> host 
   <router_IP_address> eq 443
access-list 101 deny tcp any any eq 443

Obtaining Fixed Software

Cisco has released free software updates that address these vulnerabilities. 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/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 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 agreements 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 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 acquire 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

Customers should have their product serial number available and be prepared to give the URL of this notice as evidence of 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 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 public announcements or malicious use of the vulnerability described in this advisory.

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:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-ssl

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-bulletins@lists.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.


Revision History

Revision 1.1

2009-April-16

Removed references to the combined software table, as it is now outdated

Revision 1.0

2008-September-24

Initial 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 http://www.cisco.com/web/about/security/psirt/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.


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