NTP BUG 2947: ntpq protocol vulnerable to replay attacks

Last update: February 15, 2022 20:59 UTC (43fbd379b)


Resolved 4.2.8p6 19 Jan 2016
References Bug 2947 CVE-2015-8140
Affects All ntp-4 releases up to, but not including 4.2.8p6. Resolved in 4.2.8p6.
CVSS2 Score MED 5.4 AV:A/AC:M/Au:N/C:P/I:P/A:P
CVSS3 Score MED 5.3 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N


The ntpq protocol is vulnerable to replay attacks. The sequence number being included under the signature fails to prevent replay attacks for two reasons. Commands that don’t require authentication can be used to move the sequence number forward, and NTP doesn’t actually care what sequence number is used so a packet can be replayed at any time. If, for example, an attacker can intercept authenticated reconfiguration commands that would. for example, tell ntpd to connect with a server that turns out to be malicious and a subsequent reconfiguration directive removed that malicious server, the attacker could replay the configuration command to re-establish an association to malicious server. Yes, this is an unlikely scenario, but it could still happen.



This weakness was discovered by Matt Street of Cisco ASIG.