r1 - 2016-04-27 - 02:33:34 - HarlanStennYou are here: NTP >  Main Web > SecurityNotice > NtpBug3012
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-4.2.8p11 was released on 27 February 2018. It addresses 2 low-/medium-, 1 informational-/medium-, and 2 low-severity security issues in ntpd, 1 medium-severity security issue in ntpq, and provides over 65 non-security bugfixes and other improvements over 4.2.8p10.

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 3012

Sybil vulnerability: ephemeral association attack

  • Date Resolved: Stable (4.2.8p7) 26 Apr 2016; Dev (4.3.92) 26 Apr 2016
  • References: Sec 3012 / CVE-2016-1549 / VU#718152
  • Affects: All ntp-4 releases up to, but not including 4.2.8p7, and 4.3.0 up to, but not including 4.3.92
  • CVSS2: LOW 3.5 - (AV:N/AC:M/Au:S/C:N/I:P/A:N)
  • CVSS3: MED 5.3 - (CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N)
  • Summary: ntpd can be vulnerable to Sybil attacks. If a system is set up to use a trustedkey and if one is not using the feature introduced in ntp-4.2.8p6 allowing an optional 4th field in the ntp.keys file to specify which IPs can serve time, a malicious authenticated peer -- i.e. one where the attacker knows the private symmetric key -- can create arbitrarily-many ephemeral associations in order to win the clock selection of ntpd and modify a victim's clock.
  • Mitigation:
    • Implement BCP-38.
    • Use the 4th argument in the ntp.keys file to limit the IPs that can be time servers.
    • Properly monitor your ntpd instances
  • Credit: This weakness was discovered by Matthew Van Gundy of Cisco ASIG.
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