Advisory ID: cisco-sa-19980513-wccp-auth
For Public Release 1998 May 13 15:00 UTC (GMT)
Cisco's Cisco Cache Engine product provides transparent caching for
world-wide web pages retrieved via HTTP. The Cache Engine uses a Cisco
proprietary protocol called the Web Cache Control Protocol (WCCP) to
communicate with a properly-configured Cisco router and register as a cache
service provider. The router then diverts HTTP traffic to the Cache Engine.
Although this process is not enabled by default, and takes place only
if a user specifically configures the router to enable WCCP, there is no
authentication in WCCP itself. A router configured to support Cache Engines
will treat any host that sends it valid WCCP hello packets as a cache engine,
and may divert HTTP traffic to that host. This means that it is possible for
malicious users to divert web traffic passing through such a router, even
though they may not have either physical or configuration access to the router.
This attack can be avoided by using access lists to prevent WCCP
traffic from untrusted hosts from reaching the router. Cisco will be modifying
WCCP to include hash-based authentication in a future release.
This advisory is posted at
This section provides details on affected products.
All users of the Cisco Cache Engine and WCCP who have not configured
filtering access lists to prevent WCCP access by unauthorized hosts are
affected by this attack.
Users who have not specifically configured their routers to enable WCCP
are not affected by this attack. If the character string
"wccp" does not appear in your router configuration file, you are not affected.
No other Cisco products are currently known to be affected by these
This vulnerability has been assigned Cisco bug ID
CSCdk07174. If you are a
CCO user and you have logged in, you can view bug details.
Cisco has provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.
CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.
Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.
Cisco has provided an FAQ to answer additional questions regarding CVSS at
Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
Attackers can cause a router configured for WCCP to divert some or all
HTTP traffic to any host they choose, anywhere on the Internet. Once having
done this, attackers are able to:
intercept confidential information, including site access
substitute data of their own choosing for the actual content of web
disrupt web service for connections passing through the targeted
In order to do this, the attacker would either need a Cisco Cache
Engine or software capable of generating WCCP traffic. Cisco sells Cache
Engines to the general public, although a relatively small number have been
shipped thus far. The WCCP protococol specification is unpublished, but the
protocol is not immune to reverse engineering.
This vulnerability affects all versions of Cisco IOS software that
support WCCP that have been released as of the date of this notice. This
includes Cisco IOS 11.2(P) releases beginning with 11.2(10)P, 11.1CA releases
beginning with 11.1(14)CA, and 11.1 releases derived from 11.1(14)CA, including
Cisco plans to release software that supports authentication for WCCP.
This will involve a modification to the WCCP protocol. In order to take
advantage of the authentication features, customers will need to upgrade the
software in both routers and Cache Engines, and will need to make some minor
configuration changes on both devices. Release of the improved software is
tentatively scheduled for September, 1998, but this schedule is subject to
change. Cisco believes that the workaround described below will adequately
protect Cache Engine users until the new software is ready.
Cisco is considering making an interim fix involving an explicit
command to apply an access list to all incoming WCCP traffic. This would be
largely equivalent to the workaround discussed below, but might be easier for
some users to configure. No decision has been made on when or whether to offer
this interim fix. If an interim fix is created, this notice will be updated to
reflect that fact.
WCCP runs over UDP at port 2048. By blocking unauthorized UDP traffic
destined to port 2048 on the router running WCCP, attackers can be prevented
from sending WCCP traffic to the router, and therefore from diverting any
actual traffic. For proper security, it's important to block all traffic
destined for port 2048 at any address assigned to the router, as well as at all
broadcast addresses for networks on which the router may be attached, and all
multicast addresses to which the router may be listening. The blocking can be
configured either using inbound access lists on the WCCP router itself, or
using access lists or other filtering on surrounding devices.
Cisco has made free software available to address this vulnerability
for affected customers. Prior to deploying software, customers should consult
their maintenance provider or check the software for feature set compatibility
and known issues specific to their environment.
Customers may only install and expect support for the feature sets they
have purchased. By installing, downloading, accessing or otherwise using such
software upgrades, customers agree to be bound by the terms of Cisco's software
license terms found at
or as otherwise set forth at Cisco.com Downloads at
Do not contact either "email@example.com" or "firstname.lastname@example.org"
for software upgrades.
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 website at
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 guidance and assistance with the appropriate course of
action in regards to this advisory.
The effectiveness of any workaround or fix is dependent on specific
customer situations such as product mix, network topology, traffic behavior,
and organizational mission. Due to the variety of affected products and
releases, customers should consult with their service provider or support
organization to ensure any applied workaround or fix is the most appropriate
for use in the intended network before it is deployed.
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)
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.
for additional TAC contact information, including special localized telephone
numbers and instructions and e-mail addresses for use in various
Cisco has had no reports of malicious exploitation of this
Cisco knows of no public announcements of this vulnerability before the
date of this notice. However, the vulnerability has been independently
identified by several people both inside and outside of Cisco, and should be
considered to be public knowledge.
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In addition to this CCO version of the field notice, the initial
version of this notice is also being sent via e-mail to the following
Identified Cisco Cache Engine customers. Cisco does not guarantee its
ability to identify every person or organization that may be in possesssion of
a Cache Engine, nor to exclude every person or organization that does not have
a Cache Engine.
email@example.com (includes CERT/CC)
Internal Cisco mailing lists
Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on mailing lists or
newsgroups. Users concerned about this problem are encouraged to check the
above URL for any updates.
This advisory is posted on Cisco's worldwide website at
Initial released version
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