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Cisco Security Advisory: A Vulnerability in IOS Firewall Feature Set
Revision 1.0
For Public Release 2001 November 28 08:00 (UTC -0800)
Summary
The IOS Firewall Feature set, also known as Cisco Secure Integrated
Software, also known as Context Based Access Control, and introduced
in IOS version 11.2P, has a vulnerability which permits traffic
normally expected to be denied by the dynamic access control lists.
This vulnerability is documented as Cisco Bug ID CSCdv48261.
No other Cisco product is vulnerable.
There is no workaround.
This advisory is available at the
http://www.cisco.com/warp/public/707/IOS-cbac-dynacl-pub.shtml
Affected Products
Only configurations implementing CBAC are affected. An affected
configuration includes the lines "ip inspect" in your router's
configuration. Here is one example:
ip inspect name rule1 udp
ip inspect name rule1 tcp
!
!
interface FastEthernet0/1
ip address 1.2.3.4 255.255.255.0
ip inspect rule1 in
duplex auto
speed auto
!
The filename of the router image, available via "show version"
command, includes an "o" in the section between the hyphens, if the
software includes the IOS Firewall Featureset, as in the following
example.
Router>show version
Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IO3-M), Version 12.1(5)T, RELEASE
SOFTWARE (fc1)
(the rest is truncated)
In this example the image file name is c2600-io3-m. Since it has an
"o" in its name, this image can support CBAC. For additional
information regarding Cisco IOS image identifiers consult the document
at http://www.cisco.com/warp/public/620/5.shtml#identifiers. The
major affected Cisco IOS trains are:
* 11.2P
* 11.3T
* 12.0, 12.0T
* 12.1, 12.1T, 12.1E
* 12.2, 12.2T
In addition to these, several Early Deployment (also known as X
releases) are affected. The complete list is given in the Software
Versions and Fixes section of this advisory.
Affected hardware models are:
* Cisco routers in the following series: 800, 820, 950, 1400, 1600,
1700, 2500, 2600, 3600, 4000 Gateway, 4224, 7100, 7200, 7400,
7500, SOHO 70, ubr900, ICS7750.
* The Catalyst 5000 and 6000 if they are running Cisco IOS software.
No other Cisco products are affected.
Details
Cisco IOS Firewall is a packet inspection system. It is also a
stateful system; it keeps information about connections that last
beyond the lifetime of a single packet. CBAC is an IP-only feature. A
router running CBAC recognizes Transmission Control Protocol (TCP),
User Datagram Protocol (UDP), and some higher-layer protocols, and
examines packet data beyond the IP headers. If configured, CBAC
maintains session information based on packets examined.
When a session is initiated from the protected network, CBAC creates a
dynamic access list entry allowing return traffic for that session.
Upon inspection of the return traffic through a dynamic access list,
source and destination addresses and ports are checked, however IP
protocol type is not checked. This could allow a packet of different
protocol type into the protected network.
This vulnerability is documented as Cisco Bug ID CSCdv48261.
Impact
By allowing packets of different type into the protected network, the
customer is exposed to much bigger threat. This vulnerability can be
expoited for recoinassance purposes, but only for a single port and
host that initiated a sesion in the first place. Depending on the
exact session parameters, it may be possible to send data to processes
that were supposed to be accessible only from within the trusted
network. In the worst case, it is possible to open an interactive
session to a host on the protected network. In that case, there must
be a process running on the host that is listening to the port for
which a hole is opened by CBAC.
Software Versions and Fixes
Each row of the table describes a release train and the platforms or
products for which it is intended. If a given release train is
vulnerable, then the earliest possible releases that contain the fix
and the anticipated date of availability for each are listed in the
"Rebuild," "Interim," and "Maintenance" columns. A device running a
release in the given train that is earlier than the release in a
specific column (less than the earliest fixed release) is known to be
vulnerable. The release should be upgraded at least to the indicated
release or a later version (greater than the earliest fixed release
label).
When selecting a release, keep in mind the following definitions:
Maintenance
Most heavily tested and highly recommended release of any
label in a given row of the table.
Rebuild
Constructed from the previous maintenance or major
release in the same train, it contains the fix for a
specific defect. Although it receives less testing, it
contains only the minimal changes necessary to effect the
repair.
Interim
Built at regular intervals between maintenance releases
and receives less testing. Interims should be selected
only if there is no other suitable release that addresses
the vulnerability. Interim images should be upgraded to
the next available maintenance release as soon as
possible. Interim releases are not available via
manufacturing, and usually they are not available for
customer download from CCO without prior arrangement with
the Cisco TAC.
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. If the information is not clear, contact
the Cisco TAC for assistance as shown in the following section.
More information on Cisco IOS release names and abbreviations is
available at http://www.cisco.com/warp/public/620/1.html.
+-------+------------+-----------------------------------------------------+
| |Description | |
| Train |of Image or | Availability of Fixed Releases* |
| | Platform | |
+-------+------------+------------------+-----------------+----------------+
|11.x-based Releases | Rebuild | Interim** | Maintenance |
+-------+------------+------------------+-----------------+----------------+
| |Early | |
| 11.2P |Deployment: |End of Support |
| |limited |Upgrade recommended to 12.0 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| 11.3T |Deployment: |End of Support |
| |limited |Upgrade recommended to 12.0 |
| |platforms | |
+-------+------------+------------------+-----------------+----------------+
|12.0-based Releases | Rebuild | Interim** | Maintenance |
+-------+------------+------------------+-----------------+----------------+
| |General | | | |
| |deployment | |12.0(20.3) |12.0(21) |
| 12.0 |release for | |Available |Available |
| |all | |2001-November-26 |2002-January-07 |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | |
| 12.0T |Deployment: |Not scheduled |
| |various |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XA |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XB |(ED) for |Not scheduled |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XC |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XD |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XE |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XG |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XI |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XK |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XM |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XQ |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XR |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.0XV |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1 |
| |platforms | |
+-------+------------+------------------+-----------------+----------------+
|12.1-based Releases | Rebuild Interim** Maintenance |
+-------+------------+------------------+-----------------+----------------+
| |Limited | | | |
| |deployment | | |12.1(12) |
| 12.1 |release for |12.1(11a) |12.1(11.1) |Available |
| |all | | |2001-December-03|
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Core/ISP | | | |
| 12.1E |support: | |12.1(9.6)E |12.1(10)E |
| |GSR, RSP, | | | |
| |c7200 | | | |
+-------+------------+------------------+-----------------+----------------+
| |Catalyst | | | |
| 12.1E |6000 |12.1(8a)E5 | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | |
| |Deployment | |
| |(ED): VPN, | |
| 12.1T |Distributed |End of Engineering |
| |Director, |Upgrade recommended to 12.2 |
| |various | |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.1XB |(ED) for |Not scheduled |
| |selected |Upgrade recommended to 12.1(5)YB1 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.1XC |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.2 |
| |platforms | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.1(2)XF5 | | |
|12.1XF |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.1(3)XG6 | | |
|12.1XG |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | |
| |Deployment | |
|12.1XH |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.2 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.1XI |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.2 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.1XJ |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.1(5)YB |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.1XK |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.2 |
| |platforms | |
+-------+------------+-----------------------------------------------------+
| |Early | |
| |Deployment | |
|12.1XL |(ED) for |End of Engineering |
| |selected |Upgrade recommended to 12.2 |
| |platforms | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.1(5)XM6 | | |
|12.1XM |(ED) for |Available | | |
| |selected |2001-December-03 | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | |
| |Deployment | |
|12.1XP |(ED) for |Not scheduled |
| |selected |Migrate to 12.2T |
| |platforms | |
+-------+------------+------------------+-----------------+----------------+
| |Early | |
| |Deployment | |
|12.1XT |(ED) for |Not scheduled |
| |selected |Migrate to 12.2T |
| |platforms | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.1(5)YB5 | | |
|12.1YB |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.1(5)YC2 | | |
|12.1YC |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment | | | |
|12.1YE |(ED) for |12.1(5)YE4 | | |
| |selected | | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.1(5)YF3 | | |
|12.1YF |(ED) for |Available | | |
| |selected |2001-November | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
|12.2-based Releases | Rebuild | Interim** | Maintenance |
+-------+------------+------------------+-----------------+----------------+
| |Limited | | | |
| |deployment | | |12.2(6) |
| 12.2 |release for | |12.2(5.7) |Available |
| |various | | |2001-November-12|
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | |
| |Deployment | |
|12.2DD |(ED) for |Not scheduled |
| |selected |Upgrade recommended to 12.2(4)B |
| |platforms | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |deployment | | |12.2(7) |
| 12.2T |release for |12.2(4)T1 |12.2(5.7)T |Available |
| |various | | |2002-February |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.2(2)XD3 | | |
|12.2XD |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.2(1)XE2 | | |
|12.2XE |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.2(2)XH2 | | |
|12.2XH |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.2(2)XI1 | | |
|12.2XI |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.2(2)XJ1 | | |
|12.2XJ |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.2(2)XK5 | | |
|12.2XK |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| |Early | | | |
| |Deployment |12.2(2)XQ2 | | |
|12.2XQ |(ED) for |Available | | |
| |selected |2002-January | | |
| |platforms | | | |
+-------+------------+------------------+-----------------+----------------+
| Notes |
| |
|* All dates are estimates and subject to change. |
| |
|** Interim releases are subjected to less rigorous testing than regular |
|maintenance releases, and may have serious bugs. |
+--------------------------------------------------------------------------+
Obtaining Fixed Software
Cisco is offering free software upgrades to eliminate 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 through the Software Center on Cisco's Worldwide
Web site at http://www.cisco.com.
Customers whose Cisco products are provided or maintained through
prior or existing agreement with third-party support organizations
such as Cisco Partners, authorized resellers, or service providers
should contact that support organization for assistance with the
upgrade, which should be free of charge.
Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third party
vendors but are unsuccessful at obtaining fixed software through their
point of sale 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
Please have your product serial number available and 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 either "psirt@cisco.com" or
"security-alert@cisco.com" for software upgrades.
Workarounds
There is no workaround.
Exploitation and Public Announcements
This vulnerability was discovered by a customer. The Cisco PSIRT is
not aware of any public announcements or malicious use of the
vulnerability described in this advisory.
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.
A standalone copy or paraphrase of the text of this security advisory
that omits the distribution URL in the following section is an
uncontrolled copy, and may lack important information or contain
factual errors.
Distribution
This notice will be posted on Cisco's Worldwide Web site at
http://www.cisco.com/warp/public/707/IOS-cbac-dynacl-pub.shtml. In
addition to Worldwide Web posting, a text version of this notice is
clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients:
* cust-security-announce@cisco.com
* bugtraq@securityfocus.com
* first-teams@first.org (includes CERT/CC)
* cisco@spot.colorado.edu
* comp.dcom.sys.cisco
* firewalls@lists.gnac.com
* 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 2001-November-28 08:00 GMT-0800 Initial public release
Cisco Security Procedures
Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and
registering to receive security information from Cisco, is available
on Cisco's Worldwide Web site at
http://www.cisco.com/warp/public/707/sec_incident_response.shtml.
This includes instructions for press inquiries regarding Cisco
security notices.
All Cisco Security Advisories are available at
http://www.cisco.com/go/psirt
_________________________________________________________________
This notice is Copyright 2001 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,
and include all date and version information.
_________________________________________________________________
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