Summary

• Certain Cisco products containing support for the Secure Shell (SSH) server are vulnerable to a Denial of Service (DoS) if the SSH server is enabled on the device. A malformed SSH packet directed at the affected device can cause a reload of the device. No authentication is necessary for the packet to be received by the affected device. The SSH server in Cisco IOSŪ is disabled by default.

  Cisco will be making free software available to correct the problem as soon as possible.

  The malformed packets can be generated using the SSHredder test suite from Rapid7, Inc. Workarounds are available. The Cisco PSIRT is not aware of any malicious exploitation of this vulnerability.

  This advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20021219-ssh-packet.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  Multiple Cisco products which contain support for an SSH server are vulnerable if the SSH server is enabled.

  Cisco products which are vulnerable include:

  • Cisco Routers and Catalyst Switches running affected versions of Cisco IOS shown in the Software Version and Fixes section below
    
  • Cisco Content Service Switch Models CSS11501, CSS11503, and CSS11506 running Cisco WebNS 5.10, 5.20, or 7.10
    
  • Cisco Aironet 1200 Series Access Points running 12.00T or 12.01T
    
  • Cisco Aironet 350 Series Access Points running 12.00T or 12.01T
    
  • Cisco Aironet 340 Series Access Points running 12.00T or 12.01T
    
  • Cisco Aironet 350 Series Wireless Bridges running 12.00T or 12.01T
    
  • Cisco PIX Firewall
    
  • Cisco ONS products: ONS15454, ONS15327 and ONS15600
    
  • Firewall Services Module (FWSM) for Cisco Catalyst 6500 Switches and Cisco 7600 Series Routers
    

  Products Confirmed Not Vulnerable

  Cisco products which contain SSH server functionality that are confirmed not to be vulnerable include:

  • Cisco Catalyst Switches running Cisco CatOS
    
  • Cisco VPN3000 series concentrators
    
  • Cisco Secure Intrusion Detection System (NetRanger) appliance
    
  • Cisco Secure Intrusion Detection System Catalyst Module
    
  • Cisco SN5400 Series Storage Routers
    
  • CiscoWorks 1105 Wireless LAN Solution Engine (WLSE)
    
  • CiscoWorks 1105 Hosting Solution Engine (HSE)
    
  • Cisco ONS products: ONS15310
    
  • Cisco ONS products: ONS15530, ONS15540
    

Details

• A suite of crafted packets has been developed to test implementations of the Secure Shell (SSH) protocol. If the SSH server has been enabled, several of the test cases cause a forced reload of the device before the authentication process is called. Each time an SSH connection attempt is made to a affected Cisco device with one of the crafted packets, the device may hang or reboot.

  Cisco IOS Software

  The SSH server feature is available in the following Cisco IOS release trains: 12.0S, 12.0ST, 12.1T, 12.1E, 12.2, 12.2T, 12.2S. All releases which have the SSH server feature are vulnerable when the SSH server is enabled by issuing the command crypto key generate rsa in configuration mode.

  All products running vulnerable versions of Cisco IOS except the Cisco 3550 will automatically reload and resume service following the crash. The Cisco 3550 will not reload, and will require manual intervention to resume normal processing.

  Multiple Cisco IOS defects have been discovered. They are documented as CSCdz60229, CSCdy87221 and CSCdu75477.

  Cisco Content Switching Software

  Cisco Content Services Switches running vulnerable versions of Cisco WebNS software will reload and resume services.

  This Cisco defect is documented in DDTS CSCdz62330.

  Cisco Aironet Software

  The SSH server feature was introduced as a feature in version 12.00T of the Aironet Software. Only versions 12.00T and 12.01T are vulnerable. Cisco Aironet Access Point devices running these vulnerable versions of Cisco Aironet software will reload and resume services.

  This Cisco defect is documented in DDTS CSCdz66748.

  Cisco PIX Firewall

  A malformed SSH packet may cause the PIX to reload. In some circumstances, using CiscoWorks 2000 to monitor the PIX via SSH, can also cause the PIX to reload.

  This Cisco defect is documented in DDTS CSCdz07673

  Cisco ONS Products

  A malformed SSH packet may cause the ONS product to reload. The SSH server feature was introduced as a feature in version 4.6.0 of the ONS System Software. Versions 4.6.0, 4.6.1 and 4.7.0 are vulnerable.

  This Cisco defect is documented in DDTS CSCed38362.

  Cisco Firewall Services Module (FWSM)

  A malformed SSH packet may cause the FWSM to reload. In some circumstances, using CiscoWorks 2000 to monitor the FWSM via SSH, can also cause the FWSM to reload.

  This Cisco defect is documented in DDTS CSCeb16775.

Workarounds

• Cisco IOS Software

  Workarounds consist of disabling the SSH server, removing SSH as a remote access method, permitting only trusted hosts to connect to the server, and blocking SSH traffic to the device completely via external mechanisms.

  Caution: The following workaround will have undesirable side effects for IPSEC sessions that terminate on the device that use RSA key pairs for device authentication, or that use certificates based on those RSA key pairs. IPSEC sessions using other authentication methods will not be affected.

  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 may also be disabled via removing SSH as a valid transport protocol. This 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:

  /en/US/products/hw/switches/ps628/products_configuration_guide_chapter09186a00800d84c8.html#xtocid14

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

  http://www.cisco.com/warp/public/707/confaccesslists.html

  An example of a VTY access-list can be found here:

  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
  end 

  Cisco Aironet Software

  Cisco Aironet Access Points offer an IP Port Filter feature which may be used to mitigate an attack against an access point. Information on the configuration of IP Port filters can be found in the Access Point Configuration Guide:

  http://www.cisco.com/univercd/cc/td/doc/product/wireless/airo_350/accsspts/ap350scg/ap350ch5.htm

  You may also block inbound SSH connections for your device with an external packet filtering device such as a firewall or a router that blocks traffic to TCP port 22.

  Cisco PIX Firewall

  Restrict access to the PIX SSH interface to allow connections only from trusted hosts and/or use HTTPS instead. Have CiscoWorks use Telnet to contact the PIX and restrict access to the PIX Telnet interface to allow connections only from the CiscoWorks workstation.

  Cisco ONS Products

  Block inbound SSH connections for the node with an external packet filtering device such as a firewall or a router that blocks traffic to TCP port 22.

  Cisco Firewall Services Module (FWSM)

  Restrict access to the FWSM SSH interface to allow connections only from trusted hosts and/or use HTTPS instead. Have CiscoWorks use Telnet to contact the PIX and restrict access to the PIX Telnet interface to allow connections only from the CiscoWorks workstation.

Fixed Software

• Cisco IOS Software

  The SSH server feature is available beginning in the following Cisco IOS releases: 12.0(5)S, 12.0(16)ST, 12.1(1)T, 12.1(5a)E, 12.2(1), 12.2(1)T, 12.2(1)S. All of these versions are vulnerable if the SSH feature is enabled.

  Each row of the Cisco IOS software table (below) describes a release train and the platforms or products for which it is intended. 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," "Interim," 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). When selecting a release, keep in mind the following definitions:

  Maintenance

  Most heavily tested, stable, and highly recommended release of a release train in any given row of the table.

  Rebuild

  Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific defect. Although it receives less testing, it contains only the minimal changes necessary to repair the vulnerability.

  Interim

  Built at regular intervals between maintenance releases and receives less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability. Interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available through manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco TAC.

  In all cases, customers should exercise caution to confirm that the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new software release. If the information is not clear, contact the Cisco TAC for assistance as shown in the Obtaining Fixed Software section below.

  More information on Cisco IOS software release names and abbreviations is available at http://www.cisco.com/warp/public/620/1.html.

  The fixes will be available at the Software Center located at http://www.cisco.com/tacpage/sw-center/.

  For software installation and upgrade procedures, see http://www.cisco.com/warp/public/130/upgrade_index.shtml.

  For a current view of all posted and repaired images for Cisco IOS, please check the listing available to registered CCO users at:

  Train or Release	Description or Platform	Availability of First Fixed Releases*
  12.0 Releases		Rebuild	Interim**	Maintenance
  12.0S	Core/ISP support: GSR, RSP, c7200	12.0(21)S6
  		2003-Jan-27
  		12.0(22)S4
  		2003-Mar
  		12.0(23)S2
  		2003-Feb-17
  12.0ST	Early Deployment release	12.0(20)ST7
  		2003-Jan-27
  		12.0(21)ST6
  		2003-Feb-03
  12.1 Releases		Rebuild	Interim**	Maintenance
  12.1E	Early Deployment release	12.1(13)E3
  		On CCO
  		12.1(14)E1
  		2003-Feb
  12.1EA	Early Deployment release	12.1(13) EA1
  		2003-Mar
  12.1T	Early Deployment release all major platforms	Vulnerable
  		Not Planned
  12.2 Releases		Rebuild	Interim**	Maintenance
  12.2	Major release for all platforms	12.2(12b)
  		On CCO
  		12.2(13a)
  		2003-Feb-07
  12.2S	Core ISP support			12.2(14)S
  				2003-Jan-27
  12.2T	Early deployment release all major platforms	12.2(11)T3
  		On CCO
  		12.2(13)T1
  		2003-Feb-03
  NOTES:
  * All dates are tentative and subject to change.
  ** Interim releases receive less testing than Maintenance or Rebuild releases. Interim release labels are provided to identify vulnerable pre-existing Interim releases. A first fixed Interim release should be used only when no other suitable release is available.

  Cisco Content Switching Software

  This vulnerability is fixed in the Cisco WebNS software which, according to its current schedule, will be available for download in January 2003. Interim Software releases of 5.20.0.06s and 7.10.0.06s are available now for download.

  Cisco Aironet Software

  This vulnerability is fixed in the Cisco Aironet software rebuild version 12.01T1. This software is expected to be available in late January 2003 and will be available for download from the Software Center.

  Cisco PIX Firewall

  This vulnerability is fixed in software versions 6.0(4.101), 6.1(5), 6.2(3) and 6.3(1).

  Cisco ONS Products

  This vulnerability is fixed in software versions 4.6.2, 5.0.0 and later releases.

  Cisco Firewall Services Module (FWSM)

  This vulnerability is first fixed in software version 2.2(1).

Exploitation and Public Announcements

• Cisco PSIRT is not aware of any malicious exploitation of this vulnerability. This suite of crafted packets from Rapid7, Inc. has been publicly announced via CERT/CC advisory CA-2002-36, and is available from the researcher's website. Cisco was initially listed in the CERT/CC advisory as not vulnerable based on initial testing of the suite, however upon continued internal testing it was determined that some products were vulnerable.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20021219-ssh-packet

Revision History

• Revision Number 1.7	2005-October-19	Added Cisco Firewall Services Module (FWSM) to the Affected Products, Details, Sofware Versions and Fixes, and Workarounds sections.
  Revision Number 1.6	2005-October-12	Added Cisco ONS product references to the Affected Products, Details, Sofware Versions and Fixes, and Workarounds sections.
  Revision Number 1.5	2003-October-28	Updated entry for Software Release 12.1EA
  Revision Number 1.4	2003-October-13	Corrected status for Cisco PIX Firewall - changed to affected.
  Revision Number 1.3	2003-January-24	Updated fixed software for Aironet devices, status changed to Final
  Revision Number 1.2	2003-January-16	Updated list of affected products and fixed software to include Content Service Switches and Wireless Access Points
  Revision Number 1.1	2002-December-20	Updated list of affected products to include HSE and WLSE
  Revision Number 1.0	2002-December-19	Initial Public Release

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