Code: kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
{
	struct ssh *ssh = ctxt;
	struct kex *kex = ssh->kex;
	const u_char *ptr;
	u_int i;
	size_t dlen;
	int r;

	debug("SSH2_MSG_KEXINIT received");
 	if (kex == NULL)
 		return SSH_ERR_INVALID_ARGUMENT;
 
 	ptr = sshpkt_ptr(ssh, &dlen);
 	if ((r = sshbuf_put(kex->peer, ptr, dlen)) != 0)
 		return r;

	/* discard packet */
	for (i = 0; i < KEX_COOKIE_LEN; i++)
		if ((r = sshpkt_get_u8(ssh, NULL)) != 0)
			return r;
	for (i = 0; i < PROPOSAL_MAX; i++)
		if ((r = sshpkt_get_string(ssh, NULL, NULL)) != 0)
			return r;
	/*
	 * XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
	 * KEX method has the server move first, but a server might be using
	 * a custom method or one that we otherwise don't support. We should
	 * be prepared to remember first_kex_follows here so we can eat a
	 * packet later.
	 * XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
	 * for cases where the server *doesn't* go first. I guess we should
	 * ignore it when it is set for these cases, which is what we do now.
	 */
	if ((r = sshpkt_get_u8(ssh, NULL)) != 0 ||	/* first_kex_follows */
	    (r = sshpkt_get_u32(ssh, NULL)) != 0 ||	/* reserved */
	    (r = sshpkt_get_end(ssh)) != 0)
			return r;

	if (!(kex->flags & KEX_INIT_SENT))
		if ((r = kex_send_kexinit(ssh)) != 0)
			return r;
	if ((r = kex_choose_conf(ssh)) != 0)
		return r;

	if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL)
		return (kex->kex[kex->kex_type])(ssh);

	return SSH_ERR_INTERNAL_ERROR;
}

Vulnerability Type: DoS 
CWE ID: CWE-399
Summary: ** DISPUTED ** 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.*
Commit Message: upstream commit

Unregister the KEXINIT handler after message has been
received. Otherwise an unauthenticated peer can repeat the KEXINIT and cause
allocation of up to 128MB -- until the connection is closed. Reported by
shilei-c at 360.cn

Upstream-ID: 43649ae12a27ef94290db16d1a98294588b75c05