NTP BUG 2947: ntpq protocol vulnerable to replay attacks
Last update: June 28, 2022 20:06 UTC (57417e17c)
Summary
Description
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.
Mitigation
- Configure
ntpd to get time from multiple sources.
- Use restrict statments in your
ntp.conf file to limit who is allowed to issue ntpq queries and remote configuration commands.
- Monitor your
ntpd instances.
Credit
This weakness was discovered by Matt Street of Cisco ASIG.
Timeline