Summary

• Multiple vulnerabilities have been identified and fixed in CBOS, an operating system for the Cisco 600 family of routers.

  • Cisco CBOS Software contains a flaw that permits the successful prediction of TCP Initial Sequence Numbers. It only affects the security of TCP connections that originate or terminate on the affected Cisco device itself; it does not apply to TCP traffic forwarded through the affected device in transit between two other hosts.
    This vulnerability is documented as Cisco bug ID CSCds16078.
    
  • A Cisco 600 router may stop passing the traffic and responding to the console when an ECHO REQUEST packet with the record route option is routed through it.
    This vulnerability is documented as Cisco bug ID CSCds30150.
    
  • Passwords, exec and enable, are stored in the cleartext in the NVRAM.
    This vulnerability is documented as Cisco bug ID CSCdt04882.
    
  • When multiple, large ECHO REPLY packets are routed through an affected Cisco 600 router, it will enter the ROMMON mode and stop passing any further traffic.
    This vulnerability is documented as Cisco bug ID CSCds74567.
    

  The following releases of CBOS are containing all of mentioned vulnerabilities: 2.0.1, 2.1.0, 2.1.0a, 2.2.0, 2.2.1, 2.2.1a, 2.3, 2.3.2, 2.3.5, 2.3.7 and 2.3.8.

  These vulnerabilities are fixed in the following CBOS releases: 2.3.9, 2.4.1 and 2.4.2. Customers are urged to upgrade to releases that are not vulnerable as shown in detail in the section Software Versions and Fixes below.

  This advisory is available at the https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010522-cbos.

Affected Products

• This section provides details on affected products.

  Vulnerable Products

  The affected models are: 627, 633, 673, 675, 675E, 677, 677i and 678.

  These models are vulnerable if they run any of the following, or earlier, CBOS releases: 2.0.1, 2.1.0, 2.1.0a, 2.2.0, 2.2.1, 2.2.1a, 2.3, 2.3.2, 2.3.5, 2.3.7 and 2.3.8.

  These vulnerabilities are fixed in the following CBOS releases: 2.3.9, 2.4.1 and 2.4.2.

  Products Confirmed Not Vulnerable

  No other releases of CBOS software are affected by these vulnerabilities. No other Cisco products are currently known to be affected by these vulnerabilities.

Details

• CSCds16078

  See also https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010301-ios-tcp-isn-random

  TCP sequence numbers are 32-bit integers in the circular range of 0 to 4,294,967,295. The host devices at both ends of a TCP connection exchange an Initial Sequence Number (ISN) selected at random from that range as part of the setup of a new TCP connection.

  This method provides reasonably good protection against accidental receipt of unintended data. However, to guard against malicious use, it should not be possible for an attacker to infer a particular number in the sequence. If the initial sequence number is not chosen randomly or if it is incremented in a non-random manner between the initialization of subsequent TCP sessions, then it is possible, with varying degrees of success, to forge one half of a TCP connection with another host in order to gain access to that host, or hijack an existing connection between two hosts in order to compromise the contents of the TCP connection. To guard against such compromises, ISNs should be generated as randomly as possible.

  CSCds30150

  By sending ICMP ECHO REQUEST packets (ping) with the IP Record Route option set it is possible to freeze a Cisco 600 router. This can be done either by sending the specially crafted packet or by specifying the "-r" option on the most ping programs. The packet should not be destined to a router itself.

  CSCdt04882

  The exec and enable passwords are stored in the cleartext in NVRAM. Similarly, they are also stored in the cleartext in the configuration file if one is stored on a computer. Anyone who is in a position to see a router's configuration, either directly from the device or in the file on a computer, can learn the passwords.

  This vulnerability is corrected by storing only an MD5 hash of the password in both NVRAM and in the configuration file, and the plaintext password itself is never retained.

  CSCds74567

  When multiple ICMP ECHO REPLY packets, non standard size, are passed through the affected device the device will stop passing any further traffic. Packets must be larger than the usual size (64 bytes) but that can be easily accomplished either by crafting packets or by adjusting the response size, either via command line or by modifying the program source.

Workarounds

• CSCds16078

  There is no workaround.

  CSCds30150

  There is no workaround.

  CSCdt04882

  There is no workaround.

  CSCds74567

  There is no workaround.

Fixed Software

• The following table summarizes the CBOS software releases affected by the vulnerabilities described in this notice and scheduled dates on which the earliest corresponding fixed releases will be available.

  Major Release	Description or Platform	Availability of Repaired Releases
  		General Availability (GA)
  All releases	All platforms	2.3.9 2001-MAR-19
  All releases	All platforms	2.4.1 2000-DEC-11
  All releases	All platforms	2.4.2 2001-MAY-14

Exploitation and Public Announcements

• Vulnerabilitiy CSCds30150 has been made public on VULN-DEV list.

  Altough we have not seen public discussion of vulnerability CSCdt04882 we understand that it is commonly known among users.

  Vulnerability CSCds74567 has been reported to us by a customer.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010522-cbos

Revision History

• Revision 1.1	2001-July-26	Changed Obtaining Fixed Software section to include the TAC contacts within the text paragraph instead of separated out in a list. Removed line in that same section about free software upgrades.
  Revision 1.0	2001-May-22	Initial public release.

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