FreeBSD Security Advisory - A crafted malicious authenticated mode 6 packet from a permitted network address can trigger a NULL pointer dereference. Note for this attack to work, the sending system must be on an address from which the target ntpd(8) accepts mode 6 packets, and must use a private key that is specifically listed as being used for mode 6 authorization. The ntpd daemon can crash due to the NULL pointer dereference, causing a denial of service.
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