r1 - 2016-04-27 - 02:39:23 - HarlanStennYou are here: NTP >  Main Web > SecurityNotice > NtpBug3007
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.

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NTP Bug 3007

CRYPTO-NAK DoS

  • Date Resolved: Stable (4.2.8p7) 26 Apr 2016; Dev (4.3.92) 26 Apr 2016
  • References: Sec 3007 / CVE-2016-1547 / 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: MED 4.3 (AV:N/AC:M/Au:N/C:N/I:N/A:P)
  • CVSS3: LOW 3.7 (CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L)
  • Summary: For ntp-4 versions up to but not including ntp-4.2.8p7, an off-path attacker can cause a preemptable client association to be demobilized by sending a crypto NAK packet to a victim client with a spoofed source address of an existing associated peer. This is true even if authentication is enabled.

    Furthermore, if the attacker keeps sending crypto NAK packets, for example one every second, the victim never has a chance to reestablish the association and synchronize time with that legitimate server.

    For ntp-4.2.8 thru ntp-4.2.8p6 there is less risk because more stringent checks are performed on incoming packets, but there are still ways to exploit this vulnerability in versions before ntp-4.2.8p7.
  • Mitigation:
  • Credit: This weakness was discovered by Stephen Gray and Matthew Van Gundy of Cisco ASIG.
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