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-4.2.8p10 was released on 21 March 2017. It addresses 6 medum- 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 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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