Summary

• A defect in multiple releases of Cisco IOS software will cause a Cisco router or switch to halt and reload if the IOS HTTP service is enabled, browsing to "http://router-ip/anytext?/" is attempted, and the enable password is supplied when requested. This defect can be exploited to produce a denial of service (DoS) attack.

  The vulnerability, identified as Cisco bug ID CSCdr91706, affects virtually all mainstream Cisco routers and switches running Cisco IOS software releases 12.0 through 12.1, inclusive. This is not the same defect as CSCdr36952.

  The vulnerability has been corrected and Cisco is making fixed releases available for free to replace all affected IOS releases. Customers are urged to upgrade to releases that are not vulnerable to this defect as shown in detail below.

  This vulnerability can only be exploited if the enable password is known or not set.

  The complete advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20001025-ios-http-server-query.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  The following products are affected if they run a Cisco IOS software release that has the defect. To determine if a Cisco product is running an affected IOS, log in to the device and issue the command show version. Cisco IOS software will identify itself as "Internetwork Operating System Software" or "IOS (tm)" software and will display a version number. Other Cisco devices either will not have the command show version, or will give different output. Compare the version number obtained from the router with the versions presented in the Software Versions and Fixes section below.

  Cisco devices that may be running with affected IOS software releases include:

  • Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 800, ubr900, 1000, 1400, 1500, 1600, 1700, 2500, 2600, 3000, 3600, 3800, 4000, 4500, 4700, AS5200, AS5300, AS5800, 6400, 7000, 7200, ubr7200, 7500, and 12000 series.
    
  • Most recent versions of the LS1010 ATM switch.
    
  • The Catalyst 6000 if it is running IOS.
    
  • The Catalyst 2900XL LAN switch only if it is running IOS.
    
  • The Catalyst 1900, 2800, 2900, 3000, and 5000 series LAN switches are affected.
    
  • The Cisco DistributedDirector.
    

  For some products, the affected software releases are relatively new and may not be 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 products that do not run Cisco IOS software and are not affected by this defect include, but are not limited to:

  • 700 series dialup routers (750, 760, and 770 series) are not affected.
    
  • The Catalyst 6000 is not affected if it is not running IOS.
    
  • WAN switching products in the IGX and BPX lines are not affected.
    
  • The MGX (formerly known as the AXIS shelf) is not affected.
    
  • The Cisco PIX Firewall is not affected.
    
  • The Cisco LocalDirector is not affected.
    
  • The Cisco Cache Engine is not affected.
    

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

Details

• The HTTP server was introduced in IOS release 11.0 to extend router management to the worldwide Web. The "?" (question mark) character is defined in the HTML specifications as a delimiter for CGI arguments. It is also interpreted by the IOS command-line interface as a request for help.

  As of Cisco IOS Software Release 12.0T, the meaning of a question mark when it appears adjacent to a "/" (slash) character cannot be determined properly by the URI parser in affected versions of Cisco IOS software. When a URI containing "?/" is presented to the HTTP service on the router and a valid enable password is supplied, the router enters an infinite loop. A watchdog timer expires two minutes later and forces the router to crash and reload. The router continues to be vulnerable to this defect as long as it is running an affected IOS software release and the enable password is known.

  This vulnerability may only be exploited if the enable password is not set, it is well known, or it can be guessed.

  In rare cases, an affected device fails to reload, which means an administrator must physically cycle the power to resume operation.

  The HTTP server is not enabled by default except on unconfigured Cisco model 1003, 1004, and 1005 routers. Once initial access is granted to configure the router, the customer may set an enable password, and disable or limit access to the HTTP server by changing the configuration. Once the new configuration has been saved, the HTTP server will not be enabled when the router restarts.

  The Cisco Bug ID CSCdr91706 relates to fixes for IOS; the fixes for the affected switch product lines are listed with Cisco Bug ID CSCds57774 and CSCdv38391.

Workarounds

• In lieu of an upgrade, the threat may be eliminated or reduced by taking any of the following measures:

  • Select and configure strong enable passwords on networking devices.
    Or
    
  • Disable the HTTP server using the command no ip http server while in global configuration mode.
    Or
    
  • If the HTTP server must remain enabled while unrepaired, network access to it can be controlled by applying a standard access list to the HTTP service itself. For example, if the router's HTTP service should be reachable only from a browser running on a computer at IP address 10.1.2.3, then use the following commands in global configuration mode to create a standard access list and apply it to the HTTP server:
    

         access-list 1 permit 10.1.2.3 
         ip http access-class 1
    

    If access list 1 is already in use, then choose another number in the range 0-99. The implicit deny rule added to the end of every access list will prevent access from other IP addresses.
    Or
    
  • Prevent network access to a vulnerable HTTP server by blocking traffic in the network path to the server's port with an extended access list. Such a list would be applied on an interface of the vulnerable router itself or on another Cisco router in the path of a potential attack, e.g., applied inbound on the outside interface of an edge router. The port number used in the extended access list statement must be the default port used by the HTTP server, port 80, or equal to whatever value it may have been set via the ip http port command. Use this workaround with great care; it cannot be recommended confidently without knowledge of specific customer network configurations.
    

  Save the resulting configuration in memory so that protection of the server is not inadvertently removed after a reload.

Fixed Software

• The following table summarizes the Cisco IOS software releases affected by the defect described in this notice and scheduled dates on which the earliest corresponding fixed releases will be available. Dates are tentative and subject to change.

  Each table row shows the earliest release that contains the fix in the "Rebuild", "Interim", or "Maintenance" columns, presented in release number order.

  A Maintenance Release is the most heavily tested and highly recommended release.

  A Rebuild Release is constructed from a previous maintenance or mainline release and contains a code fix for a specific defect. Although it receives less testing than a maintenance release, it is built from a previous maintenance release and includes minimum changes to address a specific defect.

  An Interim Release has much less testing than a maintenance release and should be selected only if no other suitable release fixes the defect.

  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.

  Major Release	Description or Platform	Availability of Repaired Releases*
  Unaffected Earlier Releases		Rebuild	Interim**	Maintenance
  11.0 & earlier, all variants	Numerous	Not vulnerable	Not vulnerable	Not vulnerable
  11.1	11.1 AA, 11.1 CA, 11.1 CC, 11.1 CT, 11.1 IA	Not vulnerable	Not vulnerable	Not vulnerable
  11.2	11.2 BC, 11.2 P, 11.2 F, 11.2 GS, 11.2 WA3, 11.2 XA	Not vulnerable	Not vulnerable	Not vulnerable
  11.3	11.3 NA, 11.3 AA, 11.3 DA, 11.3 XA, 11.3 HA, 11.3 WA, 11.3 MA, 11.3 DB	Not vulnerable	Not vulnerable	Not vulnerable
  Pre 12.0-based Releases		Rebuild	Interim**	Maintenance
  11.2 SA
  12.0-based Releases		Rebuild	Interim**	Maintenance
  12.0	General Deployment (GD): all platforms	Not vulnerable	Not vulnerable	Not vulnerable
  12.0DA	xDSL support: 6100, 6200	Not vulnerable	Not vulnerable	Not vulnerable
  12.0S	Core/ISP support: gsr, rsp, c7200	Not vulnerable	Not vulnerable	Not vulnerable
  12.0SC	Cable/broadband ISP: ubr7200	Not vulnerable	Not vulnerable	Not vulnerable
  12.0SL	10000 ESR: c10k	Not vulnerable	Not vulnerable	Not vulnerable
  12.0T	Early Deployment(ED): VPN, Distributed director, various platforms			12.1(5)
  				2000-OCT-30
  12.0W5	cat8510c, cat8540c, c6msm ls1010, cat8510m, cat8540m c5atm, c5atm, c3620, c3640, c4500, c5rsfc, c5rsm, c7200, rsp			12.0(13)W5(19)
  				2000-NOV-13
  	cat2948g, cat4232			12.0(10)W5(18e)
  				2000-NOV-14
  12.0XA	Early Deployment (ED): limited platforms			12.1(5)
  12.0XE	Early Deployment (ED): limited platforms	12.1(3a)E4
  		2000-OCT-24
  12.0XH	Early Deployment (ED): limited platforms	12.0(4)XH4
  		Unknown
  12.0XJ	Early Deployment (ED): limited platforms	12.0(5)XJ6
  		Unknown
  12.1-based Releases		Rebuild	Interim**	Maintenance
  12.1	General Deployment (GD) candidate: all platforms			12.1(05)
  				2000-OCT-30
  12.1AA	Access & Dial Early Deployment (ED): c5200, c5300, c5800, dsc-c5800			12.1(5)AA
  				2000-NOV-13
  12.1DA	xDSL support: 6160, 6260			12.01(04)DA
  				2000-OCT-30
  12.1DB	xDSL support: c6400			12.01(4)DB
  				2000-NOV-13
  12.1DC	xDSL NRP support: c6400r			12.01(4)DC
  				2000-NOV-13
  12.1E	ELB Early Deployment (ED): cat6k, 8500, ls1010, 7500, 7200, 7100	12.1(3a)E4
  		2000-OCT-24
  12.1EC	Cable/broadband Early Deployment (ED): ubr7200	12.01(03a)EC1
  		Unknown
  12.1T	New technology Early Deployment (ED): all platforms			12.1(5)T
  				2000-NOV-20
  12.1XA	Early Deployment (ED): limited platforms	Not scheduled		12.1(5)T
  12.1XB	Early Deployment (ED): limited platforms	Not scheduled
  12.1XC	Early Deployment (ED): limited platforms	Not scheduled		12.1(5)T
  12.1XD	Early Deployment (ED): limited platforms	Not scheduled		12.1(5)T
  12.1XE	Early Deployment (ED): limited platforms	Not scheduled		12.1(5)T
  12.1XF	Early Deployment (ED): limited platforms	12.1(2)XF2		12.1(5)T
  		2000-NOV-13
  12.1XG	Early Deployment (ED): limited platforms	12.1(3)XG2
  		2000-NOV-13
  12.1XH	Early Deployment (ED): limited platforms	Not scheduled		12.1(5)T
  12.1XI	Early Deployment (ED): limited platforms	Not scheduled
  12.1XJ	Early Deployment (ED): limited platforms	Not scheduled
  12.1XL	Early Deployment (ED): limited platforms	Not scheduled
  12.1XP	Early Deployment (ED): limited platforms	12.1(3)XP2		12.1(5)T
  		2000-NOV-13
  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.

Exploitation and Public Announcements

• The Cisco PSIRT was alerted to this issue by CORE SDI, which discovered the issue during routine security audits on equipment. The security audit included a check for common CGI vulnerabilities against a Cisco device without a configured password; the audit attempted to browse to "http:///cgi-bin/source-help?/", which caused the device to crash and reload.

  The Cisco PSIRT has received no reports of malicious exploitation of this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20001025-ios-http-server-query

Revision History

• Revision 1.6	2006-March-17	Changed 12.XC to 12.1XC in the "Software versions and fixes" section; updated Final status text.
  Revision 1.5	2003-March-05	Added additional Bug ID's in detail section for other affected hardware.
  Revision 1.4	2002-September-25	Updated Status of This Notice section to FINAL.
  Revision 1.3	2000-November-01	Updated Affected Products section with "Catalyst 1900, 2800, 2900, 3000, and 5000 series LAN switches are affected." Removed "11.2 SA" from the list of unaffected 11.2 releases. Added "11.2 SA" to pre 12.0-based affected releases. Added availability date and upgrade version for 12.0T. Changed sentence "Select and configure strong passwords on networking devices." to "Select and configure strong enable passwords on networking devices."
  Revision 1.2	2000-October-26	Updated table info for 12.1 XF, 12.1 XG and 12.1 XP. Added Catalyst 2800 as an affected product in "Affected Products" section.
  Revision 1.1	2000-October-25	Updated table info for 12.1T and 12.1AA.
  Revision 1.0	2000-October-25	Initial public release.

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