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AUSCERT External Security Bulletin Redistribution
ESB-2009.0065 -- [Cisco]
Cisco IOS and ASA: MD5 Hashes May Allow for Certificate Spoofing
19 January 2009
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco IOS
Cisco ASA
Publisher: Cisco Systems
Operating System: Cisco
Impact: Provide Misleading Information
Reduced Security
Access: Remote/Unauthenticated
CVE Names: CVE-2004-2761
Original Bulletin:
http://tools.cisco.com/security/center/viewAlert.x?alertId=17341
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Cisco Security Response: MD5 Hashes May Allow for Certificate
Spoofing
Document ID: 109463
Revision 1.0
For Public Release 2009 January 15 1600 UTC (GMT)
Cisco Response
==============
This is the Cisco response to research done by Alexander Sotirov,
Marc Stevens, Jacob Appelbaum, Arjen Lenstra, David Molnar, Dag Arne
Osvik, and Benne de Weger pertaining to MD5 collisions in
certificates issued by vulnerable certificate authorities.
Cisco has released an IntelliShield activity bulletin detailing the
specifics of this issue. This bulletin is available at the following
link:
http://tools.cisco.com/security/center/viewAlert.x?alertId=17341
The Cisco Adaptive Security Appliance (ASA) and IOS may both serve as
certificate authorities and by default use the MD5 hashing algorithm
in the digital signatures of certificates issued to end users and
devices.
The hashing algorithm used in digital certificates on the Cisco ASA
cannot be changed; however, the ASA is unlikely to be affected by the
attacks described in this research due to the way certificates are
generated on the device. Cisco recognizes the weaknesses in MD5 and
plans to alter the signature algorithm used in digital certificates
and modify the methods utilized in creation of CA and endpoint
certificates. This will be addressed by Cisco Bug ID CSCsw88068.
The Cisco IOS CA may be vulnerable to the attack described in this
research when configured to utilize MD5 hashes in endpoint
certificates. This is the default behavior; however, the device can
be reconfigured to utilize a more secure hashing algorithm. Cisco
plans to change this default behavior and modify the methods utilized
in creation of CA and endpoint certificates. This will be addressed
by Cisco Bug ID CSCsw90626.
As a workaround, an administrator can configure IOS devices running
12.4(15)T and later to use a more secure algorithm with the hash
command, as shown in the following example:
Router(config)#crypto pki server <NAME>
Router(cs-server)#shutdown
Certificate server 'shut' event has been queued for processing.
Router(cs-server)#hash sha1
Router(cs-server)#no shutdown
Certificate server 'no shut' event has been queued for processing.
Status of this Notice: FINAL
============================
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.
Revision History
================
+---------------------------------------+
| Revision | | Initial |
| 1.0 | 2009-January-15 | 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
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