Cisco Security Advisory-
Two vulnerabilities in the Massachusetts Institute of Technology (MIT) Kerberos 5
implementation that affect Cisco VPN 3000
Series Concentrators have been announced by the MIT Kerberos Team. Cisco VPN 3000 Series Concentrators authenticating users against a Kerberos Key Distribution Center (KDC) may be vulnerable to remote code execution and to Denial of Service (DoS) attacks. Cisco has made free software available to address these problems.
Cisco VPN 3000 Series Concentrators not authenticating users against a Kerberos Key Distribution Center (KDC) are not impacted.
No exploitations of these vulnerabilities have been reported.
This advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20040831-krb5.
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This section provides details on affected products.
Vulnerable Products
The following products have their Kerberos 5 implementation based on MIT Kerberos code and are affected by these vulnerabilities:
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Cisco VPN 3000 Series Concentrators. All 4.0.x software versions
prior to 4.0.5.B and all 4.1.x software versions prior to 4.1.5.B are
vulnerable. Versions prior to 4.0.x are not vulnerable since
they do not support Kerberos authentication.
Note that vulnerable products are impacted only if they are configured to authenticate users against a Kerberos KDC.
Products Confirmed Not Vulnerable
The following products have Kerberos 5 support, but their implementation is not based on MIT Kerberos, and therefore are not affected by the vulnerabilities discussed in this advisory:
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Cisco IOS® (Kerberos support available in
release 11.2 or later)
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Cisco CatOS
The following products do not have Kerberos 5 support and therefore are not affected by these vulnerabilities:
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Cisco PIX Firewall
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Cisco Firewall Services Module (FWSM) for the Cisco Catalyst 6500
Series and Cisco 7600 Series routers
No other Cisco products are currently known to be affected by these vulnerabilities.
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Cisco VPN 3000 Series Concentrators. All 4.0.x software versions
prior to 4.0.5.B and all 4.1.x software versions prior to 4.1.5.B are
vulnerable. Versions prior to 4.0.x are not vulnerable since
they do not support Kerberos authentication.
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Kerberos is a secret-key network authentication protocol developed at the Massachusetts Institute of Technology (MIT) that uses the Data Encryption Standard (DES) cryptographic algorithm for encryption and authentication. Kerberos was designed to authenticate requests for network resources. Kerberos, like other secret-key systems, is based on the concept of a trusted third party that performs secure verification of users and services. In the Kerberos protocol, this trusted third party is called the Key Distribution Center (KDC).
The primary use of Kerberos is to verify that users and the network services they use are really who and what they claim to be. To accomplish this, a trusted Kerberos server issues tickets to users. These tickets, which have a limited lifespan, are stored in a user's credential cache and can be used in place of the standard username-and-password authentication mechanism.
The Kerberos credential scheme embodies a concept called "single logon." This process requires authenticating a user once, and then allows secure authentication (without encrypting another password) wherever that user's credential is accepted.
Vulnerable Cisco devices using versions of Kerberos based on the MIT implementation to authenticate users are affected by two vulnerabilities. The first vulnerability consists of a double-free error that can happen under certain error conditions, and that can potentially allow a remote attacker to execute arbitrary code.
The second vulnerability consists of an infinite loop in the Abstract Syntax Notation (ASN) 1 decoder that can be entered upon receipt of an ASN.1 SEQUENCE type with invalid Basic Encoding Rules (BER) encoding. This vulnerability can be exploited by an attacker impersonating a legitimate Kerberos KDC or application server to cause a client program to hang inside an infinite loop, and thus creating a Denial of Service condition. This vulnerability can also be exploited to cause a KDC or application server to hang inside an infinite loop.
More information about these MIT Kerberos vulnerabilities is available at http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2004-002-dblfree.txt
and
http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2004-003-asn1.txt
.
The information in these links is provided by MIT. The two vulnerabilities described above are documented for the Cisco VPN 3000 Series Concentrators in Bug IDs CSCef24692 ( registered customers only) (registered customers only) and CSCef24900 ( registered customers only) (registered customers only).
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There is no workaround available to mitigate the effects of this vulnerability Affected users should upgrade to a fixed version of the affected software.
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The vulnerabilities described in this advisory are fixed in software versions 4.0.5.B and later and 4.1.5.B and later of the Cisco VPN 3000 Series Concentrators. If you are currently running the identified vulnerable software, you should obtain fixed software, as detailed below.
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The Cisco PSIRT is not aware of any malicious exploitation of the vulnerabilities described in this advisory.
These vulnerabilities were reported by the MIT Kerberos Team in concert with the CERT Coordination Center.
These vulnerabilities may impact other products that are not provided by Cisco. CERT/CC is coordinating the public disclosure of the impact these vulnerabilities may have on other, non-Cisco products. This Cisco Security Advisory is being published in coordination with CERT/CC.
The MIT Kerberos Team advisories for these vulnerabilities can be found at http://web.mit.edu/kerberos/www/advisories/
(MITKRB5-SA-2004-002 and MITKRB5-SA-2004-003). The CERT/CC advisories for these vulnerabilities can be found at http://www.cert.org/advisories/
.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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