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Date: Tue, 11 Jul 2000 03:01:12 -0400
From: Cisco Systems Product Security Incident Response Team <psirt@CISCO.COM>
Subject: Cisco Security Advisory: Cisco Secure PIX Firewall TCP Reset
To: BUGTRAQ@SECURITYFOCUS.COM
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Cisco Secure PIX Firewall TCP Reset Vulnerability
Revision 1.0
For Public Release 2000 July 11 06:00 US/Eastern (UTC+0400)
------------------------------------------------------------------------
Summary
=======
The Cisco Secure PIX Firewall cannot distinguish between a forged TCP Reset
(RST) packet and a genuine TCP RST packet. Any TCP/IP connection established
through the Cisco Secure PIX Firewall can be terminated by a third party from
the untrusted network if the connection can be uniquely determined. This
vulnerability is independent of configuration. There is no workaround.
This vulnerability exists in all Cisco Secure PIX Firewall software releases
up to and including 4.2(5), 4.4(4), 5.0(3) and 5.1(1). The defect has been
assigned Cisco bug ID CSCdr11711.
This notice is posted on Cisco's Worldwide Web site at
http://www.cisco.com/warp/public/707/pixtcpreset-pub.shtml.
Affected Products
=================
Cisco Secure PIX Firewalls with software versions up to and including 4.2(5),
4.4(4), 5.0(3) and 5.1(1) are affected.
No other products are vulnerable to this defect.
Details
=======
When the Cisco Secure PIX Firewall receives a TCP Reset (RST) packet, it
evaluates that packet based on data contained in the TCP packet header: source
IP address, source port, destination IP address, and destination port. If
these four values match an entry in the stateful inspection table, the
associated connection will be reset. This affects only TCP sessions. Data
exchange based on any other protocol is not affected.
To exploit this vulnerability, an attacker would need to have or infer:
* Detailed knowledge of the connection table in the Cisco Secure PIX
Firewall prior to launching the attack
Or
* Detailed knowledge of the source and destination IP Address and ports
associated with a particular connection to be attacked
This particular vulnerability only affects the connection table (which keeps
state regarding the connections being made through the device). It does not
affect the translation table (in which address mappings are stored).
Cisco Secure PIX Firewall software has been fixed so that it now checks for
a valid sequence number before removing a connection from the connection
state table.
Impact
======
Any Cisco Secure PIX Firewall that provides external access to the Internet
and for which all of the preceding conditions are met is vulnerable to the
disruption of individual sessions.
Software Versions and Fixes
===========================
For the version listed in the left-most column below, customers should upgrade
to at least the version shown in the center column. Please note the hardware
requirements following the table.
+-----------------------------+--------------------------+---------------+
| |Projected first fixed | |
|Affected Version |regular release (fix will |Date Available |
| |carry forward into all | |
| |later versions) | |
+-----------------------------+--------------------------+---------------+
|All versions of Cisco Secure | | |
|PIX up to version 4.2(5) | | |
|(including 2.7, 3.0, 3.1, | 4.4(5) | 2000-06-09 |
|4.0, 4.1) | | |
+-----------------------------+--------------------------+---------------+
|All 4.3.x and 4.4.x versions | | |
|up to and including version | 4.4(5) | 2000-06-09 |
|4.4(4) | | |
+-----------------------------+--------------------------+---------------+
|Version 5.0.x up to and | | |
|including version 5.0(3) | 5.1(2) | 2000-06-09 |
+-----------------------------+--------------------------+---------------+
|Version 5.1.1 | 5.1(2) | 2000-06-09 |
+-----------------------------+--------------------------+---------------+
A 128MB upgrade for the PIX Firewall is necessary if:
* Version 4.3 or 4.4 is used on a PIX 'Classic'
(excluding PIX10000, PIX-510, PIX-520, and PIX-515)
Or
* Version 5.0 is used on a PIX 'Classic', PIX10000, or PIX-510
(excluding PIX-520 and PIX-515)
As with any new software installation, customers planning to upgrade should
carefully read the release notes and other relevant documentation before
beginning any upgrade. Also, it is important to be certain that the new
version of Cisco Secure PIX Firewall software is supported by your hardware
and especially that enough memory is available.
Obtaining Fixed Software
========================
Cisco is offering free software upgrades to remedy this vulnerability for all
affected customers.
Customers with contracts should obtain upgraded software through their regular
update channels. For most customers, this means that upgrades should be
obtained via the Software Center on Cisco's Worldwide Web site at
http://www.cisco.com/.
Customers without contracts should get their upgrades by contacting the Cisco
Technical Assistance Center (TAC). TAC contacts are as follows:
* +1 800 553 2447 (toll-free from within North America)
* +1 408 526 7209 (toll call from anywhere in the world)
* E-mail: tac@cisco.com
Additional contact information for the Cisco TAC for non-English speakers is
available at http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml.
Give the URL of this notice as evidence of your entitlement to a free
upgrade. Free upgrades for non-contract customers must be requested through
the TAC. Please do not contact psirt@cisco.com or security-alert@cisco.com for
software upgrades.
Workarounds
===========
There are no workarounds for this defect. Customers are urged to upgrade to
the versions of code containing the fix for CSCdr11711.
Exploitation and Public Announcements
=====================================
Cisco has received no reports of malicious exploitation of this
vulnerability. The vulnerability was reported to Cisco by a customer and has
been discussed on BUGTRAQ, a public full-disclosure security mailing list.
Status of This Notice: FINAL
============================
This is a final notice. Although Cisco cannot guarantee the accuracy of all
statements in this notice, all of the facts have been checked to the best of
our ability. Cisco does not anticipate issuing updated versions of this notice
unless there is some material change in the facts. Should there be a
significant change in the facts, Cisco may update this notice.
Distribution
============
This notice is posted at
http://www.cisco.com/warp/public/707/pixtcpreset-pub.shtml on Cisco's
Worldwide Web site. A text version of this notice will be clear-signed with
the latest Cisco PSIRT RSA PGP key and posted to the following e-mail
recipients and Usenet newsgroups:
* cust-security-announce@cisco.com
* bugtraq@securityfocus.com
* firewalls@lists.gnac.net
* first-teams@first.org (includes CERT/CC)
* cisco@spot.colorado.edu
* cisco-nsp@puck.nether.net
* comp.dcom.sys.cisco
* Various internal Cisco mailing lists
Future updates of this notice, if any, will be placed on Cisco's Worldwide Web
server, but may or may not be actively announced on mailing lists or
newsgroups. Users concerned about this problem are encouraged to check the URL
given above for any updates.
Revision History
================
+-------------+-----------+-----------------------+
|Revision 1.0 |2000-07-11 |Initial public release |
+-------------+-----------+-----------------------+
Cisco Product Security Incident Assistance Process
==================================================
The web page at
http://www.cisco.com/warp/public/707/sec_incident_response.shtml describes how
to report security vulnerabilities in Cisco products, obtain assistance with
security incidents, and register to receive product security information from
Cisco Systems, Inc., including instructions for press inquiries regarding
Cisco Security Advisories and notices. This advisory is Cisco's official
public statement regarding this vulnerability.
------------------------------------------------------------------------
This notice is Copyright 2000 by Cisco Systems, Inc. This notice may be
redistributed freely after the release date given at the top of the text,
provided that redistributed copies are complete and unmodified, including
all date and version information.
------------------------------------------------------------------------
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