Advisory ID: cisco-sa-20041102-acs-eap-tls
For Public Release 2004 November 2 15:00 UTC (GMT)
A Cisco Secure Access Control Server (ACS) that is configured to use
Extensible Authentication Protocol-Transport Layer Security (EAP-TLS) to
authenticate users to the network will allow access to any user that uses a
cryptographically correct certificate as long as the user name is valid.
Cryptographically correct means that the certificate is in
the appropriate format and contains valid fields. The certificate can be
expired, or come from an untrusted Certificate Authority (CA) and still be
Only version 3.3.1 of the Cisco Secure ACS for Windows and Cisco
Secure ACS Solution Engine is affected by this vulnerability. Cisco has made
free software available to address this problem.
This vulnerability has no effect, that is, user authentication is not
impacted, if EAP-TLS is configured in the Cisco Secure ACS with binary
comparison of user certificates as the only comparison method
and if the user entry in Lightweight Directory Access
Protocol/Active Directory (LDAP/AD) contains only valid certificates.
No exploitations of this vulnerability have been reported.
This advisory is available at
This section provides details on affected products.
Only version 3.3.1 of the Cisco Secure ACS for Windows and Cisco
Secure ACS Solution Engine is affected by the vulnerability described in this
To determine your Cisco Secure ACS software version you can log into
the Cisco Secure ACS. The first screen that is presented after a successful
login will show the version number in the following format:
CiscoSecure ACS Release 3.3(1) Build 16..
ACS versions may also be displayed as
"16" is the build number referenced on the ACS
Administration Graphical User Interface (GUI).
Cisco Secure ACS for Unix and versions of Cisco Secure ACS for Windows
and Cisco Secure ACS Solution Engine prior to, and later than, 3.3.1 are
not affected by this vulnerability. Version 3.3.1 is the first
version in the 3.3.x series and version 3.3.2 is the first one that is not
affected by this vulnerability. No other Cisco products are currently known to
be affected by this vulnerability.
Cisco Secure Access Control Server provides centralized
authentication, authorization, and accounting (AAA) services to network devices
that function as AAA clients, such as a network access servers, PIX firewalls,
routers and switches. With Cisco Secure ACS, network administrators can quickly
administer accounts and globally change levels of service offerings for entire
groups of users.
EAP is a general protocol for authentication that supports multiple
authentication methods, such as token cards, Kerberos, one-time passwords,
certificates, public key authentication and smart cards.
TLS is a protocol that provides privacy and data integrity between
client/server applications communicating over an unsecure network such as the
EAP and TLS are both IETF RFC standards. The EAP protocol carries
initial authentication information, specifically EAPOL (the encapsulation of
EAP over LANs as established by IEEE 802.1X). TLS uses certificates both for
user authentication and for dynamic ephemeral session key generation. The
EAP-TLS authentication protocol uses the certificates of Cisco Secure ACS and
of the end-user client, enforcing mutual authentication of the client and of
Cisco Secure ACS. More detailed information on EAP, TLS, and EAP-TLS can be
found in the following IETF RFCs: RFC 2284 (PPP Extensible Authentication
Protocol), RFC 2246 (The TLS Protocol), and RFC 2716 (PPP EAP TLS
The vulnerability described in this document affects user
authentication in the following way: when the EAP-TLS protocol is enabled in
version 3.3.1 of Cisco Secure ACS for Windows or Cisco Secure ACS Solution
Engine, and network devices and services are configured to authenticate users
via the ACS, access will be granted to any user that uses a certificate that is
cryptographically correct as long as the user name is valid and regardless of
whether the certificate is from a trusted Certificate Authority or whether the
certificate has expired. Cryptographically correct means
that the certificate is in the appropriate format and contains valid fields.
If EAP-TLS is configured (through the ACS global authentication page)
to perform binary comparison of user certificates as the only user certificate
comparison method, user authentication is not affected by this vulnerability,
as long as the user entry in LDAP/AD contains only valid certificates. The
reason user authentication is not affected under this scenario is that when
using the binary comparison method, the certificate that is sent by the user's
machine during the EAP-TLS conversation is also compared to the user
certificate that is stored in the user entry in the LDAP/AD.
The vulnerability described here is documented in the Cisco Bug ID
registered customers only)
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
Successful exploitation of this vulnerability could allow unauthorized
access to the entire network, provided that the Cisco Secure ACS is being used
to control network access.
The vulnerability described in this advisory is fixed in version 3.3.2
of the Cisco Secure ACS for Windows software and of the Cisco Secure ACS
Solution Engine. If you are currently running the identified vulnerable
software and are using EAP-TLS, you should obtain fixed software, as detailed
If you are running Cisco Secure ACS for Windows you can either upgrade
to version 3.3.2 or just replace the current
CSCRL.dll Windows Dynamic Link Library (DLL) in the
Windows System32 folder with a fixed DLL and restart Cisco Secure ACS for
Windows. Replacing the DLL fixes the problem and does not require a full
The DLL fix can be downloaded from
The file name is
accompanying Readme file (available from the same
location) contains detailed installation instructions.
If you are using the Cisco Secure ACS Solution Engine you can also
upgrade to version 3.3.2 or run an upgrade package to replace the affected DLL
(an upgrade package is needed because there is no access to the System32
directory when using the ACS Solution Engine.)
The upgrade package for the DLL fix can be downloaded from
The file name is CSCef62913-fix-ACSSE-v18.104.22.168.zip.
The accompanying Readme file (available from the
same location) contains detailed installation instructions.
Either upgrade method, a full upgrade to version 3.3.2, or just an
upgrade of the affected DLL, is provided free of charge.
If the user account resides in an LDAP/AD server and the user
certificate is stored in the user object in LDAP/AD, binary comparison of user
certificates can be configured in the ACS Global Authentication page as the
only allowed comparison method. This will work around the
vulnerability described in this document provided that only valid certificates
are stored in the user entry in LDAP/AD.
Please note that for this workaround to work, no other certificate
comparison methods can be enabled, that is, SAN and CN certificate comparison
must be disabled in the Global Authentication page.
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 "firstname.lastname@example.org" or "email@example.com"
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
The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerability described in this advisory.
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
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 advisory will be posted on Cisco's worldwide website 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.
firstname.lastname@example.org (includes CERT/CC)
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.
Initial public release.