Date: Thu, 20 Mar 2014 11:19:17 -0600 From: Brett Glass <brett@lariat.org> To: "Ronald F. Guilmette" <rfg@tristatelogic.com>, freebsd-security@freebsd.org Subject: Re: NTP security hole CVE-2013-5211? Message-ID: <201403201719.LAA29331@mail.lariat.net>
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At 09:56 PM 3/17/2014, Ronald F. Guilmette wrote: >(It was explained to me at the time that NTP operates a bit like DNS... >with which I am more familiar... i.e. that all outbound requests originate >on high numbered ports, well and truly away from all low numbered ports, >including, in particular, 123. I am just re-verifying that my understanding >in this regard is correct, and that my current blanket firewall rule is >fine as it stands.) Different implementations do different things in this regard. Alas, newer versions of ntpd seem to use UDP port 123 as the originating port when synchronizing with outside servers while older versions did it right and used high, ephemeral ports. This means that stateful firewalling is required for security, and even with it spoofing is still possible if the attacker can guess which servers you query. (The ones in the default FreeBSD ntp.conf file are likely to work most of the time.) We should definitely patch the ntpd that's shipped with FreeBSD to issue queries on randomly chosen ephemeral ports, as well as changing the default ntp.conf file to prevent relaying. As we've seen with DNS, UDP-based services are so ripe for attacks (due to the lack of a 3-way handshake) that they need to be protected in every way possible. --Brett Glass
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