The Network Time Protocol is used to synchronize a computer"s time with another referenced time source. These packages include the ntpd service which continuously adjusts system time and utilities used to query and configure the ntpd service. 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. 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. 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. 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. It was found that ntpd did not check whether a Message Authentication Code 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. The CVE-2015-1798 and CVE-2015-1799 issues were discovered by Miroslav Lichvar of Red Hat. 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 expected. * The ntpd service dropped incoming NTP packets if their source port was lower than 123 . With this update, ntpd no longer checks the source port number, and clients behind NAT are now able to correctly synchronize with the server. Enhancements: * This update adds support for configurable Differentiated Services Code Points in NTP packets, simplifying configuration in large networks where different NTP implementations or versions are using different DSCP values. * This update adds the ability to configure separate clock stepping thresholds for each direction . Use the stepback and stepfwd options to configure each threshold. * Support for nanosecond resolution has been added to the Structural Health Monitoring reference clock. Prior to this update, when a Precision Time Protocol 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. All ntp users are advised to upgrade to these updated packages, which contain backported patches to correct these issues and add these enhancements. 4. Solution: Before applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258 5. Bugs fixed :