===================================================================== CERT-Renater Note d'Information No. 2004/VULN464 _____________________________________________________________________ DATE : 03/11/2004 HARDWARE PLATFORM(S) : / OPERATING SYSTEM(S) : Systems running Cisco Secure ACS for Windows 3.3.1, Cisco Secure ACS Solution Engine. ====================================================================== Cisco Security Advisory: Vulnerability in Cisco Secure Access Control Server EAP-TLS Authentication Revision 1.0 For Public Release 2004 November 2 1500 UTC (GMT) - - - ---------------------------------------------------------------------- Contents Summary Affected Products Details Impact Software Versions and Fixes Obtaining Fixed Software Workarounds Exploitation and Public Announcements Status of This Notice: FINAL Distribution Revision History Cisco Security Procedures - - - ---------------------------------------------------------------------- Summary ======= 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 cryptographically correct. 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 http://www.cisco.com/warp/public/707/cisco-sa-20041102-acs-eap-tls.shtml. Affected Products ================= Vulnerable 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 document. 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 003.003(001.16), where "16" is the build number referenced on the ACS Administration Graphical User Interface (GUI). Products Confirmed Not Vulnerable - - - --------------------------------- 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. Details ======= 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 CiscoSecure 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 Internet. EAP and TLS are both IETF RFC standards. The EAP protocol carries initialauthentication 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 clientand 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 Authentication Protocol). 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 ACSfor 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, userauthentication 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 isstored in the user entry in the LDAP/AD. The vulnerability described here is documented in the Cisco Bug ID CSCef62913. Impact ====== 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. Software Versions and Fixes =========================== The vulnerability described in this advisory is fixed in version 3.3.2 ofthe 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 below. If you are running Cisco Secure ACS for Windows you can either upgrade toversion 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 upgrade. The DLL fix can be downloaded from http://www.cisco.com/pcgi-bin/tablebuild.pl/cs-acs-win. The file name is CSCef62913-fix-ACSWIN-v3.3.1.16.zip. The 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 packageis 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 http://www.cisco.com/pcgi-bin/tablebuild.pl/acs-soleng-3des. The file name is CSCef62913-fix-ACSSE-v3.3.1.16.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. Obtaining Fixed Software ======================== Customers with Service Contracts - - - -------------------------------- Customers with contracts should obtain fixed software (free of charge) 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 http://www.cisco.com. Customers using Third-party Support Organizations - - - ------------------------------------------------- Customers whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorizedresellers, or service providers should contact that support organization for assistance with the upgrade, which should be free of charge. Customers without Service Contracts - - - ----------------------------------- 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 (free of charge) 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 thisnotice 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 =========== If the user account resides in an LDAP/AD server and the user certificateis 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 workaround 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. Exploitation and Public Announcements ===================================== The Cisco PSIRT is not aware of any public announcements or malicious useof the vulnerability described in this advisory. Status of This Notice: FINAL ============================ THIS ADVISORY IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KINDOF GUARANTEE OR WARRANTY. YOUR USE OF THE INFORMATION ON THE ADVISORY OR MATERIALS LINKED FROM THE ADVISORY IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS NOTICE AT ANY TIME. Distribution ============ This advisory will be posted on Cisco's worldwide website at http://www.cisco.com/warp/public/707/cisco-sa-20041102-acs-eap-tls.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 newsrecipients. * cust-security-announce@cisco.com * first-teams@first.org (includes CERT/CC) * bugtraq@securityfocus.com * vulnwatch@vulnwatch.org * cisco@spot.colorado.edu * cisco-nsp@puck.nether.net * full-disclosure@lists.netsys.com * comp.dcom.sys.cisco@newsgate.cisco.com 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. Revision History ================ +---------------------------------------------+ | Revision | | Initial | | 1.0 | 2004-November-02 | 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 website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt. ====================================================================== ========================================================= Les serveurs de référence du CERT-Renater http://www.urec.fr/securite http://www.cru.fr/securite http://www.renater.fr ========================================================= + CERT-RENATER | tel : 01-53-94-20-44 + + 151 bd de l'Hopital | fax : 01-53-94-20-41 + + 75013 Paris | email: certsvp@renater.fr + =========================================================