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Cisco Security Response

AAA Command Authorization by-pass

Document ID: 623

http://tools.cisco.com/security/center/content/CiscoSecurityResponse/cisco-sr-20060125-aaatcl

Revision 1.0

For Public Release 2006 January 25 16:00  UTC (GMT)


Contents

Response
Additional Information
Status of this Notice: Final
Revision History
Cisco Security Procedures

Cisco Response

This is an update to the original Cisco Vendor Response posted on 2006 January 25 16:00 UTC at: http://tools.cisco.com/security/center/content/CiscoSecurityResponse/cisco-sr-20060125-aaatcl
Since the original posting, it has been discovered that some versions of Cisco IOS originally documented as fixed were still affected by this vulnerability. This new issue is being tracked with Cisco Bug ID CSCsd28570 ( registered customers only). An updated Cisco IOS "Software versions and fixes" table is within. All other relevant information remains unaltered.

A vulnerability exists within Cisco Internetwork Operating System (IOS) Authentication, Authorization, and Accounting (AAA) command authorization feature, where command authorization checks are not performed on commands executed from the Tool Command Language (Tcl) exec shell. This may allow authenticated users to bypass command authorization checks in some configurations resulting in unauthorized privilege escalation.

Devices not running AAA command authorization feature, or do not support Tcl functionality are not affected by this vulnerability.

We would like to thank Nicolas Fischbach, Senior Manager, Network Engineering Security of COLT Telecom, for reporting this issue to Cisco Systems.

We greatly appreciate the opportunity to work with researchers on security vulnerabilities, and welcome the opportunity to review and assist in product reports.

Additional Information

Details

Devices that are running AAA command authorization feature and the IOS has support for the Tcl functionality, may be affected by this vulnerability.

A device that has Tcl functionality within IOS, will accept the command tclsh and provide a command-line interface (CLI) prompt back with (tcl) in the CLI prompt. Example:

router#tclsh
router(tcl)#

If the device does not support Tcl functionality, either an error message or different output will be displayed.

The (tcl) text within the CLI prompt indicates that the user is within the Tcl Shell mode.

A system configured for AAA command authorization will have a command line in show running-configuration output, which is similar to the following:

aaa authorization commands <privilege-level> <default|list-name> <group [group-name]> 
tacacs+ [additional methods]

Example:

aaa authorization commands 15 default group tacacs+ none

Devices impacted by this vulnerability, will allow users to execute any IOS EXEC command at the users authenticated privilege level from within the Tcl shell mode. This vulnerability is documented in the following bug IDs:

A separate issue, documented below, exists that exacerbates this vulnerability. An authenticated user may be placed into Tcl Shell mode automatically (without the evidence of the (tcl) within the router prompt), without any intermediate step of manually entering into Tcl Shell mode via the tclsh command, only if a previous user goes into Tcl Shell mode and terminates the session before leaving the Tcl Shell mode.

If a privileged user initiates a Tcl Shell and exits the Tcl Shell mode without issuing the Tcl Shell command tclquit then the Tcl Shell process will remain active and attached to the corresponding virtual type terminal VTY or teletypewriter (TTY - line). The next authenticated user that accesses the device over the same line will have access to the Tcl Shell process, and combined with CSCeh73049 ( registered customers only) or CSCsd28570 ( registered customers only) may bypass AAA command. This issue is documented in the following bug ID:

This separate issue is present only in the versions of IOS listed below:

  • 12.3T based trains
  • 12.4 based trains
  • 12.2(25)S and onward trains

Vulnerable Products

  • All Cisco products that are running Cisco IOS and:
    - Have AAA command authorization feature enabled
    - The IOS has support for the Tcl functionality
    - IOS Version 12.0T or later

Products Confirmed Not Vulnerable

  • Products that are not running Cisco IOS are not affected.
  • Products running Cisco IOS versions 12.0 Mainline or earlier are not affected.
  • Products running Cisco IOS versions 12.0S are not affected.
  • Products that are running Cisco IOS are not affected unless they are configured for AAA command authorization, and support Tcl functionality.
  • Products that are running Cisco IOS XR are not affected.

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

Software Versions and Fixes

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 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).

Major Release

Availability of Repaired Releases

Affected 12.0-Based Release

Rebuild

Maintenance

12.0T

Vulnerable; migrate to 12.2(32) or later

12.0XH

Vulnerable; migrate to 12.2(32) or later

12.0XK

Vulnerable; migrate to 12.2(32) or later

12.0XL

Vulnerable; migrate to 12.2(32) or later

12.0XN

Vulnerable; migrate to 12.2(32) or later

12.0XR

Vulnerable; migrate to 12.2(32) or later

Affected 12.1-Based Release

Rebuild

Maintenance

12.1

Vulnerable; migrate to 12.2(32) or later

12.1AA

Vulnerable; migrate to 12.2(32) or later

12.1E

12.1(26)E5

 

12.1EC

Vulnerable; migrate to 12.3BC or later

12.1EZ

Vulnerable; migrate to 12.1(26)E5 or later

12.1GA

Vulnerable; migrate to 12.2(32) or later

12.1GB

Vulnerable; migrate to 12.2(32) or later

12.1T

Vulnerable; migrate to 12.2(32) or later

12.1XA

Vulnerable; migrate to 12.2(32) or later

12.1XE

Vulnerable; migrate to 12.2(32) or later

12.1XH

Vulnerable; migrate to 12.2(32) or later

12.1XI

Vulnerable; migrate to 12.2(32) or later

12.1XJ

Vulnerable; migrate to 12.3(16) or later

12.1XL

Vulnerable; migrate to 12.3(16) or later

12.1XM

Vulnerable; migrate to 12.3(16) or later

12.1XP

Vulnerable; migrate to 12.3(16) or later

12.1XQ

Vulnerable; migrate to 12.3(16) or later

12.1XS

Vulnerable; migrate to 12.2(32) or later

12.1XT

Vulnerable; migrate to 12.3(16) or later

12.1XU

Vulnerable; migrate to 12.3(16) or later

12.1XV

Vulnerable; migrate to 12.3(16) or later

12.1XW

Vulnerable; migrate to 12.2(32) or later

12.1XY

Vulnerable; migrate to 12.2(32) or later

12.1XZ

Vulnerable; migrate to 12.2(32) or later

12.1YA

Vulnerable; migrate to 12.3(16) or later

12.1YB

Vulnerable; migrate to 12.3(16) or later

12.1YD

Vulnerable; migrate to 12.3(16) or later

12.1YE

Vulnerable; migrate to 12.3(16) or later

12.1YF

Vulnerable; migrate to 12.3(16) or later

12.1YH

Vulnerable; migrate to 12.3(16) or later

12.1YI

Vulnerable; migrate to 12.3(16) or later

Affected 12.2-Based Release

Rebuild

Maintenance

12.2

 

12.2(32)

12.2B

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2BW

Vulnerable; migrate to 12.3(16) or later

12.2BY

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2DD

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2DX

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2MX

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2S

12.2(14)S16

12.2(18)S11

12.2(25)S6

12.2(30)S is vulnerable; contact TAC

12.2SU

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2SW

12.2(25)SW5

 

12.2SXB

12.2(17d)SXB9

 

12.2SXD

12.2(18)SXD6

 

12.2SXE

12.2(18)SXE3

 

12.2SXF

Vulnerable; migrate to 12.2(18)SXF4, available 29-May-2006

12.2SZ

Vulnerable; migrate to 12.2(25)S6 or later

12.2T

Vulnerable; migrate to 12.3(16) or later

12.2XA

Vulnerable; migrate to 12.3(16) or later

12.2XB

Vulnerable; migrate to 12.3(16) or later

12.2XC

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2XD

Vulnerable; migrate to 12.3(16) or later

12.2XG

Vulnerable; migrate to 12.3(16) or later

12.2XH

Vulnerable; migrate to 12.3(16) or later

12.2XJ

Vulnerable; migrate to 12.3(16) or later

12.2XK

Vulnerable; migrate to 12.3(16) or later

12.2XL

Vulnerable; migrate to 12.3(16) or later

12.2XM

Vulnerable; migrate to 12.3(16) or later

12.2XN

Vulnerable; migrate to 12.3(16) or later

12.2XQ

Vulnerable; migrate to 12.3(16) or later

12.2XS

Vulnerable; migrate to 12.3(16) or later

12.2XT

Vulnerable; migrate to 12.3(16) or later

12.2XU

Vulnerable; migrate to 12.3(16) or later

12.2XV

Vulnerable; migrate to 12.3(16) or later

12.2XW

Vulnerable; migrate to 12.3(16) or later

12.2YB

Vulnerable; migrate to 12.3(16) or later

12.2YC

Vulnerable; migrate to 12.3(16) or later

12.2YD

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YE

Vulnerable; migrate to 12.2(25)S6 or later

12.2YH

Vulnerable; migrate to 12.3(16) or later

12.2YK

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YL

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YM

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YN

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YT

Vulnerable; migrate to 12.3(16) or later

12.2YU

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YW

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YX

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YY

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2YZ

Vulnerable; migrate to 12.2(25)S6 or later

12.2ZB

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2ZC

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2ZD

Vulnerable; contact TAC

12.2ZE

Vulnerable; migrate to 12.3(16) or later

12.2ZF

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2ZH

Vulnerable; contact TAC

12.2ZJ

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2ZL

Vulnerable; contact TAC

12.2ZN

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.2ZP

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

Affected 12.3-Based Release

Rebuild

Maintenance

12.3

 

12.3(16)

12.3B

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.3T

12.3(11)T10; available 13-March-2006

 

12.3(14)T7; available 3-April-2006

 

12.3XA

Vulnerable; contact TAC

12.3XB

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.3XD

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.3XE

Vulnerable; contact TAC

12.3XF

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.3XG

Vulnerable; contact TAC

12.3XH

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.3XI

12.3(7)XI7

12.3XJ

Vulnerable; contact TAC

12.3XK

Vulnerable; contact TAC

12.3XM

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.3XQ

Vulnerable; migrate to 12.4(7), available 14-March-2006

12.3XR

Vulnerable; contact TAC

12.3XW

Vulnerable; contact TAC

12.3XY

Vulnerable; migrate to 12.3(14)T7, available 3-April-2006

12.3YA

C828: Vulnerable; migrate to 12.4(7), available 14-March-2006

SOHO9x, C82x: Vulnerable; contact TAC

12.3YF

Vulnerable; contact TAC

12.3YG

Vulnerable; contact TAC

12.3YH

Vulnerable; contact TAC

12.3YI

Vulnerable; contact TAC

12.3YJ

Vulnerable; contact TAC

12.3YK

Vulnerable; contact TAC

12.3YM

12.3(14)YM6; available 26-March-2006

 

12.3YQ

Vulnerable; contact TAC

12.3YS

Vulnerable; contact TAC

12.3YT

Vulnerable; contact TAC

12.3YU

Vulnerable; contact TAC

12.3YX

Vulnerable; contact TAC

Affected 12.4-Based Release

Rebuild

Maintenance

12.4

12.4(3d); available 21-March-2006

 
 

12.4(7); available 14-March-2006

12.4MR

Vulnerable; contact TAC

12.4T

12.4(2)T4; available 20-March-2006

 

12.4(4)T2; available 3-April-2006

 
 

12.4(6)T

12.4XA

Vulnerable; contact TAC

12.4XB

Vulnerable; contact TAC

 

Obtaining Fixed Software

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 at http://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 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.

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.

Workarounds

The effectiveness of any workaround 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 is the most appropriate for use in the intended network before it is deployed.

AAA configuration command checks

Adding IOS configuration command authorization checking with the global configuration command aaa authorization config-commands forces AAA command authorization to occur within Tcl Shell mode.

caution Caution: By enabling IOS configuration command authorization all commands within EXEC configuration mode will be subject to command authorization checks.

For further information on AAA authorization config-commands please consult: http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/secur_r/sec_a1g.htm#wp1086510.

Deny tclsh IOS command within TACACS+ user profile

By ensuring that all user profiles defined within TACACS+ do not have permission to execute the IOS EXEC command tclsh an administrator can prevent users from gaining additional command privilege escalation. Seek your vendor's TACACS+ server configuration guides to ensure this is set correctly.

caution Caution: This will only be a valid workaround if all users who may access the device do not have access to tclsh command. A single user who does have access to execute tclsh and does not exit as per the procedure described above, may unknowingly leave a Tcl Shell process running on one of the VTYs.

Role Based CLI Views

The Role-Based CLI Access feature allows the network administrator to define "views," which are a set of operational commands and configuration capabilities that provide selective or partial access to Cisco IOS EXEC and configuration (Config) mode commands. Views restrict user access to Cisco IOS command-line interface (CLI) and configuration information; that is, a view can define what commands are accepted and what configuration information is visible. Thus, network administrators can exercise better control over access to Cisco networking devices.

For further information on CLI-Views: http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hsec_c/part30/hclivws.htm.

Further Information

Cisco IOS introduced the ability to support Tool Command Language (Tcl) version 7.0 commands as part of Cisco IOS Interactive Voice Response feature in Cisco IOS version 12.0(6)T and later. See http://www.cisco.com/univercd/cc/td/doc/product/access/acs_serv/vapp_dev/tclivrpg.htm for further information.

The Cisco IOS Scripting with Tcl feature provides the ability to run Tool Command Language (Tcl) version 8.3.4 commands and was introduced from Cisco IOS version 12.3(2)T. See http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123newft/123t/123t_2/gt_tcl.htm for further information.

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.


Revision History

Revision 2.0

2006-March-01

2.0 public release.

Revision 1.1

2006-January-25

Added release 12.2T to software table.

Revision 1.0

2006-January-25

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/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.


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