Summary

• The Cisco IOS FTP Server feature contains multiple vulnerabilities that can result in a denial of service (DoS) condition, improper verification of user credentials, and the ability to retrieve or write any file from the device filesystem, including the device's saved configuration. This configuration file may include passwords or other sensitive information.

  The IOS FTP Server is an optional service that is disabled by default. Devices that are not specifically configured to enable the IOS FTP Server service are unaffected by these vulnerabilities.

  This vulnerability does not apply to the IOS FTP Client feature.

  This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070509-iosftp.

Affected Products

• Vulnerable Products

  Cisco devices running IOS and configured for FTP server functionality are affected by these issues.

  IOS versions based on 11.3, 12.0, 12.1, 12.2, 12.3 and 12.4 contain the IOS FTP server feature. The IOS FTP server feature was removed via CSCsg16908.

  Only certain IOS releases based on the above IOS trains contain the IOS FTP server feature. For a device running Cisco IOS to be vulnerable, the following command must be present in the device configuration:

  ftp-server enable
  

  Products Confirmed Not Vulnerable

  Cisco devices that do not run IOS are not affected.

  Cisco IOS devices that do not have the FTP server feature enabled are not affected.

  Cisco IOS XR is not affected.

  No other Cisco devices are known to be affected.

Details

• Multiple vulnerabilities exist in the IOS FTP Server feature. These vulnerabilities are documented with the following Cisco bug IDs:

  • CSCek55259 - Improper authorization checking in IOS FTP server
    
  • CSCse29244 - IOS reload when transferring files via FTP
    

  Due to these issues with the IOS FTP server, the feature is being removed. Cisco is considering adding fully featured and secure FTP server functionality at a later date.

  The IOS FTP Server feature removal is addressed with Cisco bug ID CSCsg16908.

  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 https://sec.cloudapps.cisco.com/security/center/cvssCalculator.x.

  CSCek55259 - Improper authorization checking in IOS FTP Calculate the environmental score of CSCek55259
  CVSS Base Score - 10
  Access Vector	Access Complexity	Authentication	Confidentiality Impact	Integrity Impact	Availability Impact	Impact Bias
  Remote	Low	Not Required	Complete	Complete	Complete	Normal
  CVSS Temporal Score - 8.3
  Exploitability		Remediation Level		Report Confidence
  Functional		Official-Fix		Confirmed

  CSCse29244 - IOS reload when transferring files via FTP Calculate the environmental score of CSCse29244
  CVSS Base Score - 2.0
  Access Vector	Access Complexity	Authentication	Confidentiality Impact	Integrity Impact	Availability Impact	Impact Bias
  Remote	Low	Required	None	None	Complete	Normal
  CVSS Temporal Score - 1.7
  Exploitability		Remediation Level		Report Confidence
  Functional		Official-Fix		Confirmed

Workarounds

• Customers can disable the use of the IOS FTP Server feature by executing the following command in configuration mode:

  no ftp-server enable
  

  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:

  https://sec.cloudapps.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20070509-iosftp

  Alternative File Transfer Mechanisms

  Cisco IOS supports multiple methods for transferring files to and from the device. One such method is Secure Copy (SCP). SCP is supported on Cisco IOS images that support strong cryptography. More information on the SCP feature can be found at the following url:

  http://www.cisco.com/en/US/docs/ios/12_2t/12_2t2/feature/guide/ftscp.html

  Another alternative is using the Trivial File Transfer Protocol (TFTP) server in IOS. Information on configuring the TFTP server can be found here:

  http://www.cisco.com/en/US/docs/ios/12_2/configfun/configuration/guide/fcf011_ps1835_TSD_Products_Configuration_Guide_Chapter.html

  If disabling the IOS FTP Server is not feasible, customers can limit FTP access to the device via one of the following mechanisms:

  Infrastructure ACLs (iACL)

  Although it is often difficult to block traffic transiting your network, it is possible to identify traffic which should never be allowed to target your infrastructure devices and block that traffic at the border of your 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 ACL example shown below should be included as part of the deployed infrastructure access-list which will protect all devices with IP addresses in the infrastructure IP address range.

  A sample access list for devices running Cisco IOS is below:

  
  !--- Permit FTP services from trusted hosts destined 
  !--- to infrastructure addresses.
  
  
  access-list 150 permit tcp TRUSTED_HOSTS MASK INFRASTRUCTURE_ADDRESSES MASK eq 21
  access-list 150 permit tcp TRUSTED_HOSTS MASK INFRASTRUCTURE_ADDRESSES MASK eq 20
  
  
  !--- Deny FTP packets from all other sources destined to infrastructure addresses.
  
  
  access-list 150 deny   tcp any INFRASTRUCTURE_ADDRESSES MASK eq 21
  access-list 150 deny   tcp any INFRASTRUCTURE_ADDRESSES MASK eq 20
  
  
  !--- Permit all other traffic to transit the device.
  
  
  access-list 150 permit IP any any
  
  interface serial 2/0
    ip access-group 150 in

  The white paper entitled "Protecting Your Core: Infrastructure Protection Access Control Lists" presents guidelines and recommended deployment techniques for infrastructure protection access lists. This white paper can be obtained here: http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801a1a55.shtml.

  Receive ACLs (rACL)

  For distributed platforms, Receive ACLs may be an option starting in Cisco IOS Software Versions 12.0(21)S2 for the 12000 (GSR), 12.0(24)S for the 7500, and 12.0(31)S for the 10720. The Receive ACL protects the device from harmful traffic before the traffic can impact the route processor. Receive ACLs are designed to only protect the device on which it is configured. On the 12000, 7500, and 10720, transit traffic is never affected by a receive ACL. Because of this, the destination IP address "any" used in the example ACL entries below only refer to the router's own physical or virtual IP addresses. Receive 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 "GSR: Receive Access Control Lists" will help you identify and allow legitimate traffic to your device and deny all unwanted packets: http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801a0a5e.shtml.

  The following is the receive path ACL written to permit this type of traffic from trusted hosts:

  
  !--- Permit FTP from trusted hosts allowed to the RP.
  
  
  access-list 151 permit tcp TRUSTED_ADDRESSES MASK any eq 21
  access-list 151 permit tcp TRUSTED_ADDRESSES MASK any eq 20
  
  
  !--- Deny FTP from all other sources to the RP.
  
  
  access-list 151 deny   tcp any any eq 21
  access-list 151 deny   tcp any any eq 20
  
  
  !--- Permit all other traffic to the RP.
  !--- according to security policy and configurations.
  
  
  access-list 151 permit ip any any
  
  
  !--- Apply this access list to the 'receive' path.
  
  
  ip receive access-list 151

  Control Plane Policing (CoPP)

  The Control Plane Policing (CoPP) feature may be used to mitigate these vulnerabilities. In the following example, only FTP traffic from trusted hosts and with 'receive' destination IP addresses is permitted to reach the route processor (RP).

  It should be noted that dropping traffic from unknown or untrusted IP addresses may affect hosts with dynamically assigned IP addresses from connecting to the Cisco IOS device.

      access-list 152 deny   tcp TRUSTED_ADDRESSES MASK any eq 21
      access-list 152 deny   tcp TRUSTED_ADDRESSES MASK any eq 20
      access-list 152 permit tcp any any eq 20
      access-list 152 permit tcp any any eq 21
      access-list 152 deny    ip any any
      !
      class-map match-all COPP-KNOWN-UNDESIRABLE
       match access-group 152
      !
      !
      policy-map COPP-INPUT-POLICY
       class COPP-KNOWN-UNDESIRABLE
        drop
      !
      control-plane
       service-policy input COPP-INPUT-POLICY

  In the above CoPP example, the ACL entries that match the exploit packets with the "permit" action result in these packets being discarded by the policy-map "drop" function, while packets that match the "deny" action are not affected by the policy-map drop function.

  CoPP is available in Cisco IOS release trains 12.0S, 12.2SX, 12.2S, 12.3T, 12.4, and 12.4T.

  Additional information on the configuration and use of the CoPP feature can be found at the following URL:

  http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6586/ps6642/prod_white_paper0900aecd804fa16a.html

Fixed Software

• 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).

  Software releases that are not listed in the below table are not affected.

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

  Major Release	Availability of Repaired Releases
  Affected 12.0-Based Release	Rebuild	Maintenance
  12.0	Vulnerable; migrate to 12.2(40a) or later
  12.0T	Vulnerable; migrate to 12.2(40a) or later
  12.0XC	Vulnerable; migrate to 12.2(40a) or later
  12.0XK	Vulnerable; migrate to 12.2(40a) or later
  12.0WC	12.0(5)WC17
  Affected 12.1-Based Release	Rebuild	Maintenance
  12.1	Vulnerable; migrate to 12.2(40a) or later
  12.1T	Vulnerable; migrate to 12.2(40a) or later
  12.1XH	Vulnerable; migrate to 12.2(40a) or later
  12.1XM	Vulnerable; migrate to 12.3(21)or later
  Affected 12.2-Based Release	Rebuild	Maintenance
  12.2	12.2(40a)	12.2(46)
  12.2T	Vulnerable; migrate to 12.3(21) or later
  12.2XA	Vulnerable; migrate to 12.3(21) or later
  12.2XG	Vulnerable; migrate to 12.3(21) or later
  12.2XT	Vulnerable; migrate to 12.3(21) or later
  12.2ZF	Vulnerable; migrate to 12.4(12) or later
  12.2ZH	Vulnerable; contact TAC
  12.2ZJ	Vulnerable; migrate to 12.4(12) or later
  12.2ZL	Vulnerable; contact TAC
  12.2ZN	Vulnerable; migrate to 12.4(12) or later
  Affected 12.3-Based Release	Rebuild	Maintenance
  12.3		12.3(21)
  12.3B	Vulnerable; migrate to 12.4(12) or later
  12.3T	Vulnerable; migrate to 12.4(12) or later
  12.3TPC	Vulnerable; contact TAC
  12.3XA	Vulnerable; contact TAC
  12.3XC	Vulnerable; contact TAC
  12.3XD	Vulnerable; migrate to 12.4(12) or later
  12.3XE	Vulnerable; contact TAC
  12.3XF	Vulnerable; migrate to 12.4(12) or later
  12.3XG	Vulnerable; contact TAC
  12.3XH	Vulnerable; migrate to 12.4(12) or later
  12.3XK	Vulnerable; migrate to 12.4(12) or later
  12.3XQ	Vulnerable; migrate to 12.4(12) or later
  12.3XR	Vulnerable; contact TAC
  12.3XS	Vulnerable; migrate to 12.4(12) or later
  12.3XX	12.3(8)XX2d
  12.3YA	Vulnerable; migrate to 12.4(12) or later
  12.3YD	Vulnerable; migrate to 12.4(11)T or later
  12.3YG	Vulnerable; migrate to 12.4(11)T or later
  12.3YH	Vulnerable; migrate to 12.4(11)T or later
  12.3YI	Vulnerable; migrate to 12.4(11)T or later
  12.3YK	Vulnerable; migrate to 12.4(11)T or later
  12.3YM	Vulnerable; contact TAC
  12.3YS	Vulnerable; migrate to 12.4(11)T or later
  12.3YT	Vulnerable; migrate to 12.4(11)T or later
  12.3YZ	Vulnerable; contact TAC
  Affected 12.4-Based Release	Rebuild	Maintenance
  12.4	12.4(10b)
  	12.4(3g)
  	12.4(7d)
  	12.4(8c)	12.4(12)
  12.4SW	Vulnerable; contact TAC
  12.4T	12.4(4)T6
  	12.4(6)T6
  	12.4(9)T2	12.4(11)T
  12.4XA	Vulnerable; migrate to 12.4(6)T6 or later
  12.4XC	12.4(4)XC6
  12.4XD	12.4(4)XD4
  12.4XE	12.4(6)XE2

Exploitation and Public Announcements

• In December of 2008, FX of Phenoelit delivered a presentation at the Chaos Communication Congress entitled 'Cisco IOS attack and defense,' during which he asserted he had devised an exploit that takes advantage of this vulnerability. No new vulnerabilities were disclosed during FX's presentation at the 2008 Chaos Communication Congress.

  http://events.ccc.de/congress/2008/Fahrplan/events/2816.en.html

  Cisco is not aware of any malicious exploitation of this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070509-iosftp

Revision History

• Revision 1.4	2009-January-09	Updated the Exploitation and Public Announcements section to reflect information learned at the Dec 2008 Chaos Communication Conference.
  Revision 1.3	2008-May-14	Updates to the Workarounds > Receive ACLs section.
  Revision 1.2	2008-April-25	Updated links to the CVSS scoring for CSCek55259 and CSCse29244.
  Revision 1.1	2007-May-09	Minor grammatical and style edits
  Revision 1.0	2007-May-09	Initial public release

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