Summary

• Security Scanning software can cause a memory error in Cisco IOS® Software that will cause a reload to occur. This vulnerability affects only Cisco IOS software version 12.1(2)T and 12.1(3)T, and limited deployment releases based on those versions.

  Customers using the affected Cisco IOS software releases are urged to upgrade as soon as possible to later versions that are not vulnerable to this defect. Vulnerable products and releases are listed in detail below.

  The security scanner makes TCP connection attempts to various ports, looking for open ports to further investigate known vulnerabilities with those services associated with certain ports. However, a side effect of the tests exposes the defect described in this security advisory, and the router will reload unexpectedly as soon as it receives a request to review or write the configuration file.

  This defect is documented as Cisco Bug ID CSCds07326.

  The complete notice will be available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010524-ios-tcp-scanner-reload.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  It is impossible to list all Cisco products in this notice; the lists below include only the most commonly used or most asked-about products.

  If you are unsure whether your device is running Cisco IOS software, log into the device and issue the command show version. Cisco IOS software will identify itself simply as "IOS" or "Internetwork Operating System Software". Other Cisco devices either will not have the show version command, or will give different output.

  Cisco devices that run Cisco IOS software include the following:

  • Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 8xx, ubr9xx, 1xxx, 25xx, 26xx, 30xx, 36xx, 38xx, 40xx, 45xx, 47xx, AS52xx,
    
  • AS53xx, AS58xx, 64xx, 70xx, 72xx (including the ubr72xx), 75xx, and 12xxx series.
    
  • Most recent versions of the LS1010 ATM switch.
    
  • Some versions of the Catalyst 2900XL LAN switch.
    
  • The Cisco DistributedDirector.
    

  The affected software versions are relatively new, and are not necessarily available on every device listed above.

  Products Confirmed Not Vulnerable

  If you are not running Cisco IOS software, you are not affected by this vulnerability. Cisco devices which do not run Cisco IOS software, and are not affected by this vulnerability, include the following:

  • 7xx dialup routers (750, 760, and 770 series) are not affected.
    
  • Catalyst 19xx, 28xx, 29xx, 3xxx, and 5xxx LAN switches are not affected, except for some versions of the Catalyst 2900XL. However, optional router modules running Cisco IOS software in switch backplanes, such as the RSM module for the Catalyst 5000 and 5500, are affected.
    
  • WAN switching products in the IGX and BPX lines are not affected.
    
  • The MGX (formerly known as the AXIS shelf) is not affected.
    
  • No host-based software is affected.
    
  • The Cisco PIX Firewall is not affected.
    
  • The Cisco LocalDirector is not affected.
    
  • The Cisco Cache Engine is not affected.
    
  • The Cisco CSS 11000 series switch is not affected
    

  No other Cisco products are currently known to be affected by these vulnerabilities.

Details

• An attempt to make a TCP connection to ports 3100-3999, 5100-5999, 7100-7999, and 10100-10999 will cause the router to unexpectedly reload at the next show running-config, or write memory, or any command that causes the configuration file to be accessed. Cisco IOS software cannot be configured to support any services that might listen at those port addresses, and cannot be configured to accept connections on those ports, however, connection attempts to these ports in the affected version will cause memory corruption, later leading to an unexpected reload.

  Software packages are available from various commercial and free sites that perform automated remote tests for computer security vulnerabilities by scanning computers on a network for known security flaws. A common log message in environments that experienced security scan related crashes was the "attempt to connect to RSHELL" error message.

  • Bug ID -- This problem was introduced in 12.1(1.3)T, and is identified by Cisco Bug ID CSCds07326.
    

Workarounds

• This vulnerability can be mitigated by configuring access lists and applying access groups on all interfaces or on external devices or firewalls to prevent connection attempts to affected routers, and to eliminate router addresses in any planned security scanning exercises.

Fixed Software

• This defect was introduced in version 12.1(1.3)T, and is repaired in the following versions which are based on the 12.1(2)T and 12.1(3)T releases.

  The following table summarizes the Cisco IOS software releases that are known to be affected, and the earliest estimated dates of availability for the recommended fixed versions. Dates are always tentative and subject to change.

  Each row of the table 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 and the anticipated date of availability for each are listed in the "Rebuild", "Interim", and "Maintenance" columns. A device running any release in the given train that is earlier than the release in a specific column (less than the earliest fixed release) is known to be vulnerable, and it should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label).

  When selecting a release, keep in mind the following definitions:

  • Maintenance
    Most heavily tested and highly recommended release of any label in a 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 effect the repair.
    
  • Interim
    Built at regular intervals between maintenance releases and receive less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability, and interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available via manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco TAC.
    

  In the table below, the logical superseding software is recommended when there is no rebuild or maintenance planned for a specific software release. Customers should verify that planned upgrades will meet their requirements. For further details, see the IOS Release Notes for each Cisco IOS Train. http://www.cisco.com/univercd/cc/td/doc/product/software/index.htm. 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 TAC for assistance as shown later in this notice.

  More information on Cisco IOS Software release names and abbreviations is available at http://www.cisco.com/en/US/products/sw/iosswrel/tsd_products_support_category_home.html.

  Major Release	Description or Platform	Availability of Repaired Releases*
  Unaffected Earlier Releases		Rebuild	Interim**	Maintenance
  12.0 and earlier, all variants	Numerous	Not vulnerable	Not vulnerable	Not vulnerable
  12.1-based Releases		Rebuild	Interim**	Maintenance
  12.1	General Deployment (GD) candidate: all platforms	Not vulnerable	Not vulnerable	Not vulnerable
  12.1AA	Dial Support	Not vulnerable	Not vulnerable	Not vulnerable
  12.1CX	Core/ISP support: GSR, RSP, C7200	Not vulnerable	Not vulnerable	Not vulnerable
  12.1DA	xDSL Support: 6100, 6200	Not vulnerable	Not vulnerable	Not vulnerable
  12.1DB	Cisco 6400 Universal Access Concentrator			12.1(4)DB
  12.1DC	xDSL NRP support: c6400r			12.1(4)DC
  12.1E	Core/ISP Support: GSR, RSP, c7200	Not vulnerable	Not vulnerable	Not vulnerable
  12.1EC	Early Deployment (ED): ubr7200, UBR Headend platforms	Not vulnerable	Not vulnerable	Not vulnerable
  12.1EX	Catalyst 6000	Not vulnerable	Not vulnerable	Not vulnerable
  12.1EY	Catalyst 8510, 8540, LS1010	Not vulnerable	Not vulnerable	Not vulnerable
  12.1T	New technology Early Deployment (ED): all platforms		12.1(4.3)T	12.1(5)T
  12.1XA	Early Deployment (ED): limited platforms	Not vulnerable	Not vulnerable	Not vulnerable
  12.1XB	Early Deployment (ED): limited platforms			12.2(1)
  12.1XC	Early Deployment (ED): limited platforms			12.2(1)
  12.1XD	Early Deployment (ED): limited platforms	Not vulnerable	Not vulnerable	Not vulnerable
  12.1XE	Early Deployment (ED): limited platforms			12.2(1)
  12.1XF	Early Deployment (ED): limited platforms			12.2(1)
  12.1XG	Early Deployment (ED): limited platforms			12.2T***
  12.1XH	Early Deployment (ED): limited platforms			12.2(1)
  12.1XI	Early Deployment (ED): limited platforms			12.2(1)
  12.1XJ	Early Deployment (ED): limited platforms			12.2T***
  12.1XK	Early Deployment (ED): limited platforms			12.2(1)
  12.1XL	Early Deployment (ED): limited platforms			12.2(1)
  12.1XM	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1XP	Early Deployment (ED): limited platforms			12.2T***
  12.1XQ	Early Deployment (ED): limited platforms			12.2T***
  12.1XR	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1XS	Early Deployment (ED): limited platforms			12.1(5)XS
  12.1XT	Early Deployment (ED): limited platforms			12.2T***
  12.1XU	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1XV	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1XW	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1XX	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1XY	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1XZ	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1YA	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1YB	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1YC	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  12.1YD	Early Deployment (ED): limited platforms	Not Vulnerable	Not Vulnerable	Not Vulnerable
  Notes
  * All dates are estimated and subject to change. ** Interim releases are subjected to less rigorous testing than regular maintenance releases, and may have serious bugs. *** This release does not have a rebuild solution. Customers should upgrade to 12.2T when it becomes available. This is not a misprint.

Exploitation and Public Announcements

• The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities described in this advisory. However, many reports of reloads related to this vulnerability have been reported by customers, due to customer use of security scanning software.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010524-ios-tcp-scanner-reload

Revision History

• Revision 1.1	2001-May-24	Made changes to the workarounds section
  Revision 1.0	2001-May-24	Initial public release.

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