COMMAND
Cisco
SYSTEMS AFFECTED
CBOS 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.
PROBLEM
Following is based on a Cisco Security Advisory. 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 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. No other
releases of CBOS software are affected by these vulnerabilities.
No other Cisco products are affected by these vulnerabilities.
CSCds16078
==========
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.
Forged packets can be injected into a network from a location
outside its boundary so that they are trusted as authentic by
the receiving host, thus resulting in a failure of integrity.
Such packets could be crafted to gain access or make some other
modification to the receiving system in order to attain some
goal, such as gaining unauthorized interactive access to a
system or compromising stored data. From a position within the
network where it is possible to receive the return traffic (but
not necessarily in a position that is directly in the traffic
path), a greater range of violations is possible. For example,
the contents of a message could be diverted, modified, and then
returned to the traffic flow again, causing a failure of integrity
and a possible failure of confidentiality.
Any compromise using this vulnerability is only possible for TCP
sessions that originate or terminate on the affected Cisco device
itself. It does not apply to TCP traffic that is merely forwarded
through the device.
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.
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 exec and enable passwords. Armed with that knowledge,
an attacker can log into the device and change the router's
configuration.
This vulnerability can be even more dangerous if the ISP is using
the same passwords for all of the devices which it manages. Such
practice, using the same passwords for multiple devices, is
strongly discouraged.
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.
SOLUTION
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
below.
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.
+===========+================+=====================================+
| | | |
| Release | Description or | Availability of Repaired Releases |
| | Platform |=====================================+
| | | General Availability (GA) |
+===========+================+=====================================+
| All | All platforms | 2.3.9 |
| releases | | 2001-Mart-19 |
+-----------+----------------+-------------------------------------+
| All | All platforms | 2.4.1 |
| releases | | 2000-December-11 |
+-----------+----------------+-------------------------------------+
| All | All platforms | 2.4.2 |
| releases | | 2001-May-14 |
+===========+================+=====================================+