r1 - 2015-10-23 - 09:20:17 - HarlanStennYou are here: NTP >  Main Web > SecurityNotice > NtpBug2913
NTP users are strongly urged to take immediate action to ensure that their NTP daemons are not susceptible to being used in distributed denial-of-service (DDoS) attacks. Please also take this opportunity to defeat denial-of-service attacks by implementing Ingress and Egress filtering through BCP38.

ntp-4.2.8p10 was released on 21 March 2017. It addresses 6 medium- and 5 low-severity security issues, 4 informational security topics, 15 bugfixes, and contains other improvements over 4.2.8p9.

Please see the NTP Security Notice for vulnerability and mitigation details.

Are you using Autokey in production? If so, please contact Harlan - he's got some questions for you.

NTP Bug 2913

TALOS-CAN-0052: mode 7 loop counter underrun

  • Date Resolved: Stable (4.2.8p4) 21 Oct 2015
  • References: Sec 2913 / CVE-2015-7848
  • Affects: All ntp-4 releases up to, but not including 4.2.8p4, and 4.3.0 up to, but not including 4.3.77
  • CVSS: (AV:N/AC:H/Au:M/C:N/I:N/A:C) Base Score: 4.6
  • Summary: If ntpd is configured to enable mode 7 packets, and if the use of mode 7 packets is not properly protected thru the use of the available mode 7 authentication and restriction mechanisms, and if the (possibly spoofed) source IP address is allowed to send mode 7 queries, then an attacker can send a crafted packet to ntpd that will cause it to crash.
  • Mitigation:
    • Implement BCP-38.
    • Upgrade to 4.2.8p4, or later, from the NTP Project Download Page or the NTP Public Services Project Download Page.
    • If you are unable to upgrade:
      • In ntp-4.2.8, mode 7 is disabled by default. Don't enable it.
      • If you must enable mode 7:
        • configure the use of a requestkey to control who can issue mode 7 requests.
        • configure restrict noquery to further limit mode 7 requests to trusted sources.
    • Monitor your ntpd instances.
  • Credit: This weakness was discovered by Aleksandar Nikolic of Cisco Talos.
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