ntp (SL7)

Synopsis: Moderate: ntp security, bug fix, and enhancement update
Advisory ID: SLSA-2015:2231-4
Issue Date: 2015-11-19
CVE Numbers: CVE-2014-9298

It was found that because NTP’s access control was based on a source IP
address, an attacker could bypass source IP restrictions and send
malicious control and configuration packets by spoofing ::1 addresses.
(CVE-2014-9298, CVE-2014-9751)

A denial of service flaw was found in the way NTP hosts that were peering
with each other authenticated themselves before updating their internal
state variables. An attacker could send packets to one peer host, which
could cascade to other peers, and stop the synchronization process among
the reached peers. (CVE-2015-1799)

A flaw was found in the way the ntp-keygen utility generated MD5 symmetric
keys on big-endian systems. An attacker could possibly use this flaw to
guess generated MD5 keys, which could then be used to spoof an NTP client
or server. (CVE-2015-3405)

A stack-based buffer overflow was found in the way the NTP autokey
protocol was implemented. When an NTP client decrypted a secret received
from an NTP server, it could cause that client to crash. (CVE-2014-9297,

It was found that ntpd did not check whether a Message Authentication Code
(MAC) was present in a received packet when ntpd was configured to use
symmetric cryptographic keys. A man-in-the-middle attacker could use this
flaw to send crafted packets that would be accepted by a client or a peer
without the attacker knowing the symmetric key. (CVE-2015-1798)

Bug fixes:

* The ntpd service truncated symmetric keys specified in the key file to
20 bytes. As a consequence, it was impossible to configure NTP
authentication to work with peers that use longer keys. With this update,
the maximum key length has been changed to 32 bytes.

* The ntpd service could previously join multicast groups only when
starting, which caused problems if ntpd was started during system boot
before network was configured. With this update, ntpd attempts to join
multicast groups every time network configuration is changed.

* Previously, the ntp-keygen utility used the exponent of 3 when
generating RSA keys. Consequently, generating RSA keys failed when FIPS
mode was enabled. With this update, ntp-keygen has been modified to use
the exponent of 65537, and generating keys in FIPS mode now works as

* The ntpd service dropped incoming NTP packets if their source port was
lower than 123 (the NTP port). With this update, ntpd no longer checks the
source port number, and clients behind NAT are now able to correctly
synchronize with the server.


* This update adds support for configurable Differentiated Services Code
Points (DSCP) in NTP packets, simplifying configuration in large networks
where different NTP implementations or versions are using different DSCP

* This update adds the ability to configure separate clock stepping
thresholds for each direction (backward and forward). Use the “stepback”
and “stepfwd” options to configure each threshold.

* Support for nanosecond resolution has been added to the Structural
Health Monitoring (SHM) reference clock. Prior to this update, when a
Precision Time Protocol (PTP) hardware clock was used as a time source to
synchronize the system clock, the accuracy of the synchronization was
limited due to the microsecond resolution of the SHM protocol. The
nanosecond extension in the SHM protocol now allows sub-microsecond
synchronization of the system clock.


– Scientific Linux Development Team