The key_certify function in usr.bin/ssh/key.c in OpenSSH 5.6 and 5.7, when generating legacy certificates using the -t command-line option in ssh-keygen, does not initialize the nonce field, which might allow remote attackers to obtain sensitive stack memory contents or make it easier to conduct hash collision attacks.
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c02794777
http://kb.juniper.net/InfoCenter/index?page=content&id=JSA10673
http://secunia.com/advisories/43181
http://secunia.com/advisories/44269
https://exchange.xforce.ibmcloud.com/vulnerabilities/65163
http://www.openwall.com/lists/oss-security/2011/02/04/2