Advisory ID: cisco-sa-20000419-catos-enable-bypass
For Public Release 2000 April 19 15:00 UTC (GMT)
Cisco Catalyst software permits unauthorized access to the enable mode
in the 5.4(1) release. Once initial access is granted, access can be obtained
for the higher level "enable" mode without a password. This problem is resolved
in version 5.4(2). Customers with vulnerable releases are urged to upgrade as
soon as possible.
This vulnerability has been assigned Cisco bug ID CSCdr10025.
This advisory is posted at
This section provides details on affected products.
All users of Cisco Catalyst 4000, 5000, 5500, 6000 and 6500 with the
software version 5.4(1) only.
The affected image names are as follows:
No other releases of Cisco Catalyst software are affected by this
vulnerability. No other Cisco products are currently known to be affected by
Anyone who can obtain ordinary console access to an affected switch can
bypass password authentication to obtain "enable" mode access without knowledge
of the "enable" password. This vulnerability can be exploited through the
network using telnet or via the physical console.
This problem was introduced in software version 5.4(1), and is
corrected in version 5.4(2). Due to this defect, software version 5.4(1) is
deferred. Customers are urged to upgrade to version 5.4(2).
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
This vulnerability permits unauthorized access to the configuration
mode and unauthorized configuration changes on a Catalyst switch.
When considering software upgrades, also consult
and any subsequent advisories to determine exposure and a complete upgrade
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 Technical
Assistance Center ("TAC") or your contracted maintenance provider for
There are no known workarounds for this vulnerability. Strictly
limiting telnet access to the device will prevent the initial connection
required to exploit this vulnerability. Telnet access can be controlled with
the following command set:
set ip permit <address> <mask> telnet
set ip permit enable
This command set will deny all traffic not specified in the permit
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 Systems knows of no public discussion nor active exploits
involving this vulnerability, which was reported by several customers who
encountered it during normal use.
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A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.
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:
email@example.com (includes CERT/CC)
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.
Initial public release.