NTP contains a vulnerability in the handling of mode 7 requests, which can result in a denial-of-service condition.
NTP mode 7 (MODE_PRIVATE) is used by the ntpdc query and control utility. In contrast, ntpq uses NTP mode 6 (MODE_CONTROL), while routine NTP time transfers use modes 1 through 5. Upon receipt of an incorrect mode 7 request or a mode 7 error response from an address that is not listed in a "restrict ... noquery" or "restrict ... ignore" segment, ntpd will reply with a mode 7 error response and log a message.
If an attacker spoofs the source address of ntpd host A in a mode 7 response packet sent to ntpd host B, both A and B will continuously send each other error responses, for as long as those packets get through.
A remote, unauthenticated attacker may be able to cause a denial-of-service condition on a vulnerable NTP server.
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Thanks to Harlan Stenn for reporting this vulnerability.
This document was written by Will Dormann, based on information provided by Harlan Stenn.
|Date First Published:||2009-12-08|
|Date Last Updated:||2011-07-22 12:47 UTC|