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.

This topic: Main > SecurityNotice > NtpBug2913
Topic revision: r1 - 2015-10-23 - 09:20:17 - HarlanStenn
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