Update ntp4 package to 4.2.8p2.

NTP 4.2.8p2 (Harlan Stenn <stenn@ntp.org>, 2015/04/xx)

Focus: Security and Bug fixes, enhancements.

Severity: MEDIUM

In addition to bug fixes and enhancements, this release fixes the
following medium-severity vulnerabilities involving private key
authentication:

* [Sec 2779] ntpd accepts unauthenticated packets with symmetric key crypto.

    References: Sec 2779 / CVE-2015-1798 / VU#374268
    Affects: All NTP4 releases starting with ntp-4.2.5p99 up to but not
including ntp-4.2.8p2 where the installation uses symmetric keys
to authenticate remote associations.
    CVSS: (AV:A/AC:M/Au:N/C:P/I:P/A:P) Base Score: 5.4
    Date Resolved: Stable (4.2.8p2) 07 Apr 2015
    Summary: When ntpd is configured to use a symmetric key to authenticate
a remote NTP server/peer, it checks if the NTP message
authentication code (MAC) in received packets is valid, but not if
there actually is any MAC included. Packets without a MAC are
accepted as if they had a valid MAC. This allows a MITM attacker to
send false packets that are accepted by the client/peer without
having to know the symmetric key. The attacker needs to know the
transmit timestamp of the client to match it in the forged reply
and the false reply needs to reach the client before the genuine
reply from the server. The attacker doesn't necessarily need to be
relaying the packets between the client and the server.

Authentication using autokey doesn't have this problem as there is
a check that requires the key ID to be larger than NTP_MAXKEY,
which fails for packets without a MAC.
    Mitigation:
        Upgrade to 4.2.8p2, or later, from the NTP Project Download Page
or the NTP Public Services Project Download Page
        Configure ntpd with enough time sources and monitor it properly.
    Credit: This issue was discovered by Miroslav Lichvar, of Red Hat.

* [Sec 2781] Authentication doesn't protect symmetric associations against
  DoS attacks.

    References: Sec 2781 / CVE-2015-1799 / VU#374268
    Affects: All NTP releases starting with at least xntp3.3wy up to but
not including ntp-4.2.8p2 where the installation uses symmetric
key authentication.
    CVSS: (AV:A/AC:M/Au:N/C:P/I:P/A:P) Base Score: 5.4
    Note: the CVSS base Score for this issue could be 4.3 or lower, and
it could be higher than 5.4.
    Date Resolved: Stable (4.2.8p2) 07 Apr 2015
    Summary: An attacker knowing that NTP hosts A and B are peering with
each other (symmetric association) can send a packet to host A
with source address of B which will set the NTP state variables
on A to the values sent by the attacker. Host A will then send
on its next poll to B a packet with originate timestamp that
doesn't match the transmit timestamp of B and the packet will
be dropped. If the attacker does this periodically for both
hosts, they won't be able to synchronize to each other. This is
a known denial-of-service attack, described at
https://www.eecis.udel.edu/~mills/onwire.html .

According to the document the NTP authentication is supposed to
protect symmetric associations against this attack, but that
doesn't seem to be the case. The state variables are updated even
when authentication fails and the peers are sending packets with
originate timestamps that don't match the transmit timestamps on
the receiving side.

This seems to be a very old problem, dating back to at least
xntp3.3wy. It's also in the NTPv3 (RFC 1305) and NTPv4 (RFC 5905)
specifications, so other NTP implementations with support for
symmetric associations and authentication may be vulnerable too.
An update to the NTP RFC to correct this error is in-process.
    Mitigation:
        Upgrade to 4.2.8p2, or later, from the NTP Project Download Page
or the NTP Public Services Project Download Page
        Note that for users of autokey, this specific style of MITM attack
is simply a long-known potential problem.
        Configure ntpd with appropriate time sources and monitor ntpd.
Alert your staff if problems are detected.
    Credit: This issue was discovered by Miroslav Lichvar, of Red Hat.

* New script: update-leap
The update-leap script will verify and if necessary, update the
leap-second definition file.
It requires the following commands in order to work:

wget logger tr sed shasum

Some may choose to run this from cron.  It needs more portability testing.

(taca)