ntp -- Crafted null dereference attack from a trusted source with an authenticated mode 6 packet

Network Time Foundation reports:

A crafted malicious authenticated mode 6 (ntpq) packet from a permitted network address can trigger a NULL pointer dereference, crashing ntpd.

Note that for this attack to work, the sending system must be on an address that the target's ntpd accepts mode 6 packets from, and must use a private key that is specifically listed as being used for mode 6 authorization.

Impact: The ntpd daemon can crash due to the NULL pointer dereference, causing a denial of service.

Mitigation:

• Use restrict noquery to limit addresses that can send mode 6 queries.
• Limit access to the private controlkey in ntp.keys.
• Upgrade to 4.2.8p13, or later.

[source]