home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
InfoMagic Standards 1994 January
/
InfoMagic Standards - January 1994.iso
/
inet
/
scc
/
9227
< prev
next >
Wrap
Text File
|
1992-12-16
|
7KB
|
151 lines
**************************************************************************
Security Bulletin 9227 DISA Defense Communications System
December 11, 1992 Published by: DDN Security Coordination Center
(SCC@NIC.DDN.MIL) 1-(800) 365-3642
DEFENSE DATA NETWORK
SECURITY BULLETIN
The DDN SECURITY BULLETIN is distributed by the DDN SCC (Security
Coordination Center) under DISA contract as a means of communicating
information on network and host security exposures, fixes, and concerns
to security and management personnel at DDN facilities. Back issues may
be obtained via FTP (or Kermit) from NIC.DDN.MIL [192.112.36.5]
using login="anonymous" and password="guest". The bulletin pathname is
scc/ddn-security-yynn (where "yy" is the year the bulletin is issued
and "nn" is a bulletin number, e.g. scc/ddn-security-9227).
**************************************************************************
+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
! !
! The following important advisory was issued by the Computer !
! Emergency Response Team (CERT) and is being relayed unedited !
! via the Defense Information Systems Agency's Security !
! Coordination Center distribution system as a means of !
! providing DDN subscribers with useful security information. !
! !
+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
CA-92:20 CERT Advisory
December 10, 1992
Cisco Access List Vulnerability
-----------------------------------------------------------------------------
The CERT Coordination Center has received information concerning a
vulnerability with Cisco routers when access lists are utilized. This
vulnerability is present in Cisco software releases 8.2, 8.3, 9.0 and 9.1.
Cisco Systems and CERT strongly recommend that sites using Cisco routers
for firewalls take immediate action to eliminate this vulnerability from
their networks.
This vulnerability is fixed in Cisco software releases 8.3 (update 5.10),
9.0 (update 2.5), 9.1 (update 1.1) and in all later releases. Customers
who are using software release 8.2 and do not want to upgrade to a later
release should contact Cisco's Technical Assistance Center (TAC) at
800-553-2447 (Internet: tac@cisco.com) for more information.
The following interim releases are available via anonymous FTP from
ftp.cisco.com (131.108.1.111).
Note: this FTP server will not allow filenames to be listed or matched
with wildcards. Also, you cannot request the file by its full pathname.
You must first cd to the desired directory (beta83_dir, beta90_dir, or
beta91_dir) and then request the desired file (gs3-bfx.83-5.10, etc.).
Release (Update) Filename Size Checksum
8.3 (5.10) /beta83_dir/gs3-bfx.83-5.10 1234696 02465 1206
9.0 (2.5) /beta90_dir/gs3-bfx.90-2.5 1705364 47092 1666
9.1 (1.1) /beta91_dir/gs3-k.91-1.1 2005548 59407 1959
For those customers having a maintenance contract, these releases are also
available on Cisco's Customer Information On-Line (CIO) service.
Other customers may obtain these releases through Cisco's Technical
Assistance Center or by contacting their local Cisco distributor.
-----------------------------------------------------------------------------
I. Description
A vulnerability in Cisco access lists allows some packets that one
would expect to be filtered by the access list to be erroneously routed
and vice-versa. This vulnerability can allow unauthorized traffic
to pass through the gateway and can block authorized traffic.
II. Problem
If a Cisco router is configured to use extended IP access lists for
traffic filtering on an MCI, SCI, cBus or cBusII interface, and the IP
route cache is enabled, and the "established" keyword is used in the
access list, then the access list can be improperly evaluated. This
can permit packets that should be filtered and filter packets that
should be permitted.
III. Workaround
This vulnerability can be avoided by either rewriting the extended
access list to eliminate the "established" keyword, or by configuring
the interface to eliminate the IP route cache. To disable the IP route
cache, use the configuration command "no ip route-cache".
Example for a serial interface:
router>enable
Password:
router#configure terminal
Enter configuration commands, one per line.
Edit with DELETE, CTRL/W, and CTRL/U; end with CTRL/Z
interface serial 0
no ip route-cache
^Z
router#write memory
IV. Solution
Obtain and install the appropriate interim release listed above.
Sites that are not experienced with this installation process
should contact the TAC center at 800-553-2447 for assistance.
---------------------------------------------------------------------------
The CERT Coordination Center wishes to thank Keith Reynolds of the
Santa Cruz Operation for his assistance in identifying this problem
and Cisco Systems for their assistance in providing technical information
for this advisory.
---------------------------------------------------------------------------
If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in FIRST (Forum of Incident
Response and Security Teams).
Internet E-mail: cert@cert.org
Telephone: 412-268-7090 (24-hour hotline)
CERT personnel answer 7:30 a.m.-6:00 p.m. EST(GMT-5)/EDT(GMT-4),
on call during other hours for emergencies.
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, PA 15213-3890
Past advisories, information about FIRST representatives, and other
information related to computer security are available for anonymous FTP
from cert.org (192.88.209.5).
****************************************************************************
* *
* The point of contact for MILNET security-related incidents is the *
* Security Coordination Center (SCC). *
* *
* E-mail address: SCC@NIC.DDN.MIL *
* *
* Telephone: 1-(800)-365-3642 *
* *
* NIC Help Desk personnel are available from 7:00 a.m.-7:00 p.m. EST, *
* Monday through Friday except on federal holidays. *
* *
****************************************************************************