The kex_input_kexinit function in kex.c in OpenSSH 6.x and 7.x through 7.3 allows remote attackers to cause a denial of service (memory consumption) by sending many duplicate KEXINIT requests. NOTE: a third party reports that "OpenSSH upstream does not consider this as a security issue."

References

• http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/kex.c.diff?r1=1.126&r2=1.127&f=h
• http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/kex.c?rev=1.127&content-type=text/x-cvsweb-markup
• http://www.openwall.com/lists/oss-security/2016/10/19/3
• http://www.openwall.com/lists/oss-security/2016/10/20/1
• http://www.securityfocus.com/bid/93776
• http://www.securitytracker.com/id/1037057
• https://bugzilla.redhat.com/show_bug.cgi?id=1384860
• https://cert-portal.siemens.com/productcert/pdf/ssa-412672.pdf
• https://ftp.openbsd.org/pub/OpenBSD/patches/6.0/common/013_ssh_kexinit.patch.sig
• https://github.com/openssh/openssh-portable/commit/ec165c392ca54317dbe3064a8c200de6531e89ad

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