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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
AusCERT Security Bulletin Summary
Product: Cisco IOS
Publisher: Cisco Systems
Operating System: Cisco
Impact: Provide Misleading Information
CVE Names: CVE-2004-2761
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Cisco Security Response: MD5 Hashes May Allow for Certificate
Document ID: 109463
For Public Release 2009 January 15 1600 UTC (GMT)
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
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
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>
Certificate server 'shut' event has been queued for processing.
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
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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
| Revision | | Initial |
| 1.0 | 2009-January-15 | public |
| | | release |
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