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Posted May 19, 2002
Site cisco.com

Cisco Security Advisory - Cisco Cache Engines and Content Engines provide a transparent cache for world wide web pages retrieved via HTTP. The default configuration of the proxy feature can be abused to open a TCP connection to any reachable destination IP address and hide the true IP source address of the connection allowing for anonymous port scanning, dos attacks, spam, etc.

tags | web, tcp
systems | cisco
SHA-256 | 90dda9032936ddaa76e20df2b74ee75c7232797f81c592acdd20f58b6db84f78


Change Mirror Download

Cisco Security Advisory: Transparent Cache Engine and Content Engine TCP Relay

Revision 1.0: FINAL

For Public Release 2002 May 15 18:00 GMT

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Please provide your feedback on this document.

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Affected Products
Software Versions and Fixes
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice
Revision History
Cisco Security Procedures

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Cisco Cache Engines and Content Engines provide a transparent cache for world
wide web pages retrieved via HTTP. These products also can be configured to
transparently intercept requests to proxy servers supporting various protocols
such as HTTPS. The default configuration of the proxy feature can be abused to
open a TCP connection to any reachable destination IP address and hide the true
IP source address of the connection. This behavior has been implicated in a
variety of undesirable and possibly illegal activities such as transmitting
unsolicited commercial e-mail, unauthorized network scanning, and denial of
service attacks.

This vulnerability can be resolved in the field by changing the configuration
of the affected device. Fixed versions of the software have been modified to
provide a more secure configuration by default.

This advisory is available at

Affected Products

The following Cisco Cache Engine and Content Engine products are affected if
they are running the specified versions of software:

* Content Engine 507, 560, 590, or 7320 running cache software 2.x, 3.1,
4.0.x, or 4.1.x
* Cache Engine 505, 550, or 570 running software version 2.2.0 or above
* Content Router CR-4430 running ACNS 4.x
* Content Distribution Manager CDM-4630 or CDM-4650 running ACNS 4.x

No other Cisco products are affected by this vulnerability.


The ability to handle proxied requests was added in version 2.2.0 of the Cache
Engine software. More details are provided in the Release Notes at

In addition to caching pages from remote web servers, the cache software also
has the ability to cache data for other proxy servers using a variety of
supported protocols such as FTP and HTTPS. This function is enabled by default.
Since proxied HTTPS services may be available on a variety of ports, the device
can be instructed by a client to open a TCP connection to any reachable IP
address and port.

The following warning is displayed during configuration and the boot process
when the Cache Engine running version 2.x is configured as an HTTPS proxy
server without transparent redirection:

It is recommended to set restrictions that allow or deny HTTPS traffic to
Destination Ports. Default settings may not provide the desired security level.

This warning is not displayed when the device operated in transparent mode and
is not shown in any case when running software versions 3.x and 4.x.

This issue has been resolved by changing the default behavior when HTTPS proxy
is enabled so that connections are limited based on the destination port
numbers and connections to ports less than 1024 are denied.

This vulnerability has been assigned Cisco bug ID CSCdx05705, which modifies
the default settings to ensure the administrator must specify permitted


Cisco Cache Engines and Content Engines can be used to forward unexpected
traffic, and to obscure the true originator of undesirable traffic.

Software Versions and Fixes

This vulnerability can be corrected by customers in the field by modifying the
configuration of the device. A software upgrade is not required to address this

The default behavior is corrected in version ACNS 4.1(3.3) and will be carried
forward into all future versions.

Cache Engines CE-505, 550 and 570 cannot be upgraded to ACNS version 4.1
software, and thus only the configuration workaround will apply.

Obtaining Fixed Software

Cisco is offering free software upgrades for systems that can run ACNS software
version 4.1. The software upgrade is equivalent to manually changing the
default behavior in the device's configuration and thus corrected software is
not available for older or unsupported releases. Customers may only install and
expect support for the feature sets they have purchased.

Customers with service contracts should contact their regular update channels
to obtain the free software upgrade identified via this advisory. For most
customers with service contracts, this means that upgrades should be obtained
through the Software Center on Cisco's Worldwide Web site at

Customers whose Cisco products are provided or maintained through a 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 obtaining the free software upgrade

Customers who purchased directly 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
obtain fixed software by contacting the Cisco Technical Assistance Center (TAC)
using the contact information listed below. In these cases, customers are
entitled to obtain an upgrade to a later version of the same release or as
indicated by the applicable corrected software version in the Software Versions
and Fixes section (noted above).

Cisco 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

See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional
TAC contact information, including special localized telephone numbers and
instructions and e-mail addresses for use in various languages.

Please have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade.

Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com"
for software upgrades.


This problem can be solved by a configuration command, which blocks the use of
redirected proxy requests for any port other than 443.

https destination-port allow 443
https destination-port deny all

If the HTTPS proxy is not necessary to an installation, then the command "https
destination-port allow 443" can be excluded from the above workaround.

Exploitation and Public Announcements

The Cisco PSIRT is aware of several instances in which Cisco Cache Engines or
Content Engines have been abused to transmit unsolicited commercial e-mail and
hide the true source of the message.

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.


This notice will be posted on Cisco's Worldwide Web site at
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 |2002-May-15|Initial public release |
|1.0 |18:00 GMT | |

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 website 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/.

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This notice is Copyright 2002 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.

- -------------------------------------------------------------------------------

Version: PGP 6.5.2


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