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Cisco IOS Software Crafted Encryption Packet Denial of Service Vulnerability

Advisory ID: cisco-sa-20090923-tls

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20090923-tls

Revision 1.1

For Public Release 2009 September 23 16:00  UTC (GMT)


Summary

Cisco IOS® Software contains a vulnerability that could allow an attacker to cause a Cisco IOS device to reload by remotely sending a crafted encryption packet.

Cisco has released free software updates that address this vulnerability.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20090923-tls.

Note: The September 23, 2009, Cisco IOS Security Advisory bundled publication includes eleven Security Advisories. Ten of the advisories address vulnerabilities in Cisco IOS Software, and one advisory addresses a vulnerability in Cisco Unified Communications Manager. Each advisory lists the releases that correct the vulnerability or vulnerabilities detailed in the advisory.

Individual publication links are in "Cisco Event Response: Semiannual Cisco IOS Software Advisory Bundled Publication" at the following link:

http://www.cisco.com/web/about/security/intelligence/Cisco_ERP_ sep09.html

Affected Products

Vulnerable Products

Devices running affected versions of Cisco IOS Software are susceptible if configured with any of the following features:

  • Secure Socket Layer (SSL) Virtual Private Network (VPN)
  • Secure Shell (SSH)
  • Internet Key Exchange (IKE) Encrypted Nonces

Note: Other SSL/HTTPS related features than WebVPN and SSL VPN are not affected by this vulnerability.

To determine whether SSLVPN is enabled on a device, log in to the device and issue the command-line interface (CLI) command show running-config | include webvpn . If the device returns any output then SSLVPN is configured and the device may be vulnerable. Vulnerable configurations vary depending on whether the device is supporting Cisco IOS WebVPN (introduced in Release 12.3(14)T) or Cisco IOS SSLVPNs (introduced in Release 12.4(6)T). The following methods describe how to confirm if the device is vulnerable:

If the output from "show running-config | include webvpn" contains "webvpn enable" then the device is configured with the original Cisco IOS WebVPN. The only way to determine whether the device is vulnerable is to examine the output of "show running-config" to confirm that webvpn is enabled via the command "webvpn enable" and that a "ssl trustpoint" has been configured. The following example shows a vulnerable device configured with Cisco IOS WebVPN:

webvpn enable
!
webvpn
 ssl trustpoint TP-self-signed-29742012

If the output from "show running-config | include webvpn" contains "webvpn gateway <word>" then the device is supporting the Cisco IOS SSLVPN feature. A device is vulnerable if it has the "inservice" command in at least one of the "webvpn gateway" sections. The following example shows a vulnerable device configured with Cisco IOS SSLVPN:

Router# show running | section webvpn        
webvpn gateway Gateway
 ip address 10.1.1.1 port 443  
 ssl trustpoint Gateway-TP
 inservice
 !
Router#

A device that supports the Cisco IOS SSLVPN is not vulnerable if it has no "webvpn gateways" configured or all the configured "webvpn gateways" contain the "no inservice" webvpn gateway command.

To determine if SSH is enabled use the show ip ssh command, as shown in the following example:

Router#show ip ssh 
SSH Enabled - version 1.99
Authentication timeout: 120 secs; Authentication retries: 3
Minimum expected Diffie Hellman key size : 1024 bits

To determine if the IKE encrypted nonces feature is enabled, use the show running-config | include rsa-encr command as follows:

Router#show running-config | inc rsa-encr
 authentication rsa-encr

To determine the Cisco IOS Software release that is running on a Cisco product, administrators can log in to the device and issue the show version command to display the system banner. The system banner confirms that the device is running Cisco IOS Software by displaying text similar to "Cisco Internetwork Operating System Software" or "Cisco IOS Software." The image name displays in parentheses, followed by "Version" and the Cisco IOS Software release name. Other Cisco devices do not have the show version command or may provide different output.

The following example identifies a Cisco product that is running Cisco IOS Software Release 12.3(26) with an installed image name of C2500-IS-L:

Router#show version
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-IS-L), Version 12.3(26), RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2008 by cisco Systems, Inc.
Compiled Mon 17-Mar-08 14:39 by dchih


!--- output truncated

The following example identifies a Cisco product that is running Cisco IOS Software Release 12.4(20)T with an installed image name of C1841-ADVENTERPRISEK9-M:

Router#show version
Cisco IOS Software, 1841 Software (C1841-ADVENTERPRISEK9-M), Version 12.4(20)T, RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2008 by Cisco Systems, Inc.
Compiled Thu 10-Jul-08 20:25 by prod_rel_team


!--- output truncated

Additional information about Cisco IOS Software release naming conventions is available in "White Paper: Cisco IOS Reference Guide" at the following link: http://www.cisco.com/warp/public/620/1.html.

Products Confirmed Not Vulnerable

The Cisco ASA 5500 Series Adaptive Security Appliances are not affected by this vulnerability.

Cisco IOS XR Software is not affected by this vulnerability.

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

Details

A Cisco IOS device that is configured for SSLVPN or SSH may reload when it receives a specially crafted TCP packet on TCP port 443 (SSLVPN) or TCP port 22 (SSH). Completion of the three-way handshake to the associated TCP port number of these features is required for the vulnerability to be successfully exploited; however, authentication is not required. A Cisco IOS device that is configured for IKE encrypted nonces may reload when it receives a specially crafted UDP packet on port 500 or 4500 (if configured for NAT Traversal (NAT-T)).

This vulnerability is documented in Cisco bug ID CSCsq24002 ( registered customers only) and has been assigned the Common Vulnerabilities and Exposures (CVE) identifier CVE-2009-2871.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerability 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 .

CSCsq24002 - Crafted Encrypted packet may cause device reload

Calculate the environmental score of CSCsq24002

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

Successful exploitation of the vulnerability described in this document may result in a reload of the device. The issue could be repeatedly exploited to cause an extended DoS 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

12.2

Not Vulnerable

 

12.2B

Not Vulnerable

 

12.2BC

Not Vulnerable

 

12.2BW

Not Vulnerable

 

12.2BX

Not Vulnerable

 

12.2BY

Not Vulnerable

 

12.2BZ

Not Vulnerable

 

12.2CX

Not Vulnerable

 

12.2CY

Not Vulnerable

 

12.2CZ

Not Vulnerable

 

12.2DA

Not Vulnerable

 

12.2DD

Not Vulnerable

 

12.2DX

Not Vulnerable

 

12.2EW

Not Vulnerable

 

12.2EWA

Not Vulnerable

 

12.2EX

Not Vulnerable

 

12.2EY

Not Vulnerable

 

12.2EZ

Not Vulnerable

 

12.2FX

Not Vulnerable

 

12.2FY

Not Vulnerable

 

12.2FZ

Not Vulnerable

 

12.2IRA

Not Vulnerable

 

12.2IRB

Not Vulnerable

 

12.2IRC

Not Vulnerable

 

12.2IXA

Not Vulnerable

 

12.2IXB

Not Vulnerable

 

12.2IXC

Not Vulnerable

 

12.2IXD

Not Vulnerable

 

12.2IXE

Not Vulnerable

 

12.2IXF

Not Vulnerable

 

12.2IXG

Not Vulnerable

 

12.2IXH

Not Vulnerable

 

12.2JA

Not Vulnerable

 

12.2JK

Not Vulnerable

 

12.2MB

Not Vulnerable

 

12.2MC

Not Vulnerable

 

12.2S

Not Vulnerable

 

12.2SB

Not Vulnerable

 

12.2SBC

Not Vulnerable

 

12.2SCA

Not Vulnerable

 

12.2SCB

Not Vulnerable

 

12.2SE

Not Vulnerable

 

12.2SEA

Not Vulnerable

 

12.2SEB

Not Vulnerable

 

12.2SEC

Not Vulnerable

 

12.2SED

Not Vulnerable

 

12.2SEE

Not Vulnerable

 

12.2SEF

Not Vulnerable

 

12.2SEG

Not Vulnerable

 

12.2SG

Not Vulnerable

 

12.2SGA

Not Vulnerable

 

12.2SL

Not Vulnerable

 

12.2SM

Not Vulnerable

 

12.2SO

Not Vulnerable

 

12.2SQ

Not Vulnerable

 

12.2SRA

Not Vulnerable

 

12.2SRB

Not Vulnerable

 

12.2SRC

Not Vulnerable

 

12.2SRD

Not Vulnerable

 

12.2STE

Not Vulnerable

 

12.2SU

Not Vulnerable

 

12.2SV

Not Vulnerable

 

12.2SVA

Not Vulnerable

 

12.2SVC

Not Vulnerable

 

12.2SVD

Not Vulnerable

 

12.2SVE

Not Vulnerable

 

12.2SW

Not Vulnerable

 

12.2SX

Not Vulnerable

 

12.2SXA

Not Vulnerable

 

12.2SXB

Not Vulnerable

 

12.2SXD

Not Vulnerable

 

12.2SXE

Not Vulnerable

 

12.2SXF

Not Vulnerable

 

12.2SXH

Not Vulnerable

 

12.2SXI

Not Vulnerable

 

12.2SY

Not Vulnerable

 

12.2SZ

Not Vulnerable

 

12.2T

Not Vulnerable

 

12.2TPC

Not Vulnerable

 

12.2XA

Not Vulnerable

 

12.2XB

Not Vulnerable

 

12.2XC

Not Vulnerable

 

12.2XD

Not Vulnerable

 

12.2XE

Not Vulnerable

 

12.2XF

Not Vulnerable

 

12.2XG

Not Vulnerable

 

12.2XH

Not Vulnerable

 

12.2XI

Not Vulnerable

 

12.2XJ

Not Vulnerable

 

12.2XK

Not Vulnerable

 

12.2XL

Not Vulnerable

 

12.2XM

Not Vulnerable

 

12.2XNA

Please see Cisco IOS-XE Software Availability

 

12.2XNB

Please see Cisco IOS-XE Software Availability

 

12.2XNC

Please see Cisco IOS-XE Software Availability

 

12.2XND

Please see Cisco IOS-XE Software Availability

 

12.2XO

Not Vulnerable

 

12.2XQ

Not Vulnerable

 

12.2XR

Not Vulnerable

 

12.2XS

Not Vulnerable

 

12.2XT

Not Vulnerable

 

12.2XU

Not Vulnerable

 

12.2XV

Not Vulnerable

 

12.2XW

Not Vulnerable

 

12.2YA

Not Vulnerable

 

12.2YB

Not Vulnerable

 

12.2YC

Not Vulnerable

 

12.2YD

Not Vulnerable

 

12.2YE

Not Vulnerable

 

12.2YF

Not Vulnerable

 

12.2YG

Not Vulnerable

 

12.2YH

Not Vulnerable

 

12.2YJ

Not Vulnerable

 

12.2YK

Not Vulnerable

 

12.2YL

Not Vulnerable

 

12.2YM

Not Vulnerable

 

12.2YN

Not Vulnerable

 

12.2YO

Not Vulnerable

 

12.2YP

Not Vulnerable

 

12.2YQ

Not Vulnerable

 

12.2YR

Not Vulnerable

 

12.2YS

Not Vulnerable

 

12.2YT

Not Vulnerable

 

12.2YU

Not Vulnerable

 

12.2YV

Not Vulnerable

 

12.2YW

Not Vulnerable

 

12.2YX

Not Vulnerable

 

12.2YY

Not Vulnerable

 

12.2YZ

Not Vulnerable

 

12.2ZA

Not Vulnerable

 

12.2ZB

Not Vulnerable

 

12.2ZC

Not Vulnerable

 

12.2ZD

Not Vulnerable

 

12.2ZE

Not Vulnerable

 

12.2ZF

Not Vulnerable

 

12.2ZG

Not Vulnerable

 

12.2ZH

Not Vulnerable

 

12.2ZJ

Not Vulnerable

 

12.2ZL

Not Vulnerable

 

12.2ZP

Not Vulnerable

 

12.2ZU

Not Vulnerable

 

12.2ZX

Not Vulnerable

 

12.2ZY

Not Vulnerable

 

12.2ZYA

Not Vulnerable

 

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

Not Vulnerable

 

12.4GC

Not Vulnerable

 

12.4JA

Not Vulnerable

 

12.4JDA

Not Vulnerable

 

12.4JDC

Not Vulnerable

 

12.4JDD

Not Vulnerable

 

12.4JK

Not Vulnerable

 

12.4JL

Not Vulnerable

 

12.4JMA

Not Vulnerable

 

12.4JMB

Not Vulnerable

 

12.4JX

Not Vulnerable

 

12.4MD

12.4(15)MD3

12.4(15)MD3

12.4MDA

Not Vulnerable

 

12.4MR

12.4(19)MR3

12.4(19)MR3

12.4SW

Vulnerable; first fixed in 12.4T

12.4(15)T10

12.4(20)T4

12.4T

12.4(15)T10

12.4(22)T2

12.4(20)T3

12.4(24)T

12.4(15)T10

12.4(20)T4

12.4XA

Not Vulnerable

 

12.4XB

Not Vulnerable

 

12.4XC

Not Vulnerable

 

12.4XD

Not Vulnerable

 

12.4XE

Not Vulnerable

 

12.4XF

Vulnerable; first fixed in 12.4T

12.4(15)T10

12.4(20)T4

12.4XG

Not Vulnerable

 

12.4XJ

Vulnerable; first fixed in 12.4T

12.4(15)T10

12.4(20)T4

12.4XK

Vulnerable; first fixed in 12.4T

12.4(15)T10

12.4(20)T4

12.4XL

Not Vulnerable

 

12.4XM

Not Vulnerable

 

12.4XN

Not Vulnerable

 

12.4XP

Not Vulnerable

 

12.4XQ

12.4(15)XQ3

12.4(15)T10

12.4XR

12.4(15)XR5

12.4(15)XR7

12.4(22)XR

12.4XT

Not Vulnerable

 

12.4XV

Vulnerable; Contact your support organization per the instructions in Obtaining Fixed Software section of this advisory

 

12.4XW

Vulnerable; first fixed in 12.4T

12.4(15)T10

12.4(20)T4

12.4XY

Vulnerable; first fixed in 12.4T

12.4(15)T10

12.4(20)T4

12.4XZ

Vulnerable; first fixed in 12.4T

12.4(15)T10

12.4(20)T4

12.4YA

Vulnerable; first fixed in 12.4T

12.4(15)T10

12.4(20)T4

12.4YB

Not Vulnerable

 

12.4YD

Not Vulnerable

 

12.4YE

Not Vulnerable

 

Note: No Cisco IOS Software Modularity releases are affected by this vulnerability.

Cisco IOS XE Software

IOS XE Release

First Fixed Release

2.1.x

Not Vulnerable

2.2.x

Not Vulnerable

2.3.x

2.3.2

2.4.x

Not Vulnerable

Workarounds

There are no available workarounds other than disabling the affected features and protecting SSH access with the use of VTY access control lists.

Use the no webvpn enable command to disable SSL VPN use.

For Cisco IOS the SSH server can be disabled by applying the command crypto key zeroize rsa while in configuration mode. The SSH server is enabled automatically upon generating an RSA key pair. Zeroing the RSA keys is the only way to completely disable the SSH server.

Access to the SSH server on Cisco IOS Software may also be disabled by removing SSH as a valid transport protocol. This action can be done by reapplying the transport input command with 'ssh' removed from the list of permitted transports on vty lines while in configuration mode. For example:

line vty 0 4                                                                    
      transport input telnet                                                        
    end

If SSH server functionality is desired, access to the server can be restricted to specific source IP addresses or blocked entirely through the use of Access Control Lists (ACLs) on the vty lines as shown in the following URL: http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configuration/guide/swacl.html#xtocid14

More information on configuring ACLs can be found on Cisco's public website:

http://www.cisco.com/en/US/products/sw/secursw/ps1018/products_tech_note09186a00800a5b9a.shtml

The following is an example of a vty access-list:

access-list 2 permit 10.1.1.0 0.0.0.255
access-list 2 deny any

line vty 0 4
 access-class 2 in

In the previous example, only the 10.1.1.0/24 network is allowed to SSH to the Cisco IOS device.

To disable IKE encrypted nonces use the no authentication rsa-encr command under an ISAKMP policy, as shown in the following example:

crypto isakmp policy
 no authentication rsa-encr

Obtaining Fixed Software

Cisco has released free software updates that address this vulnerability. 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 with Service Contracts

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/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.

Exploitation and Public Announcements

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

This vulnerability was found during internal testing.

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-20090923-tls

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 1.0

2009-September-23

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.