If generating a legacy certificate using the "-t" option, a vulnerability could be exploited by attackers to gain knowledge of sensitive information. If legacy certificates have been issued using OpenSSH version 5.6/5.7, consider rotating any CA key used. OpenSSH recommend upgrading to version 5.8 available here or apply this patch.
 

[1] http://www.openssh.com/txt/legacy-cert.adv

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Guy Bruneau IPSS Inc. gbruneau at isc dot sans dot edu