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CERT Coordination Center

NTP service vulnerable to internal overflow if date / time offset is greater than 34 years

Vulnerability Note VU#584606

Original Release Date: 2004-03-05 | Last Revised: 2004-03-05


NTP (Network TIme Protocol) contains an integer overflow vulnerability that may lead to clients receiving an incorrect date/time offset.


NTP (Network Time Protocol) is a method by which client machines can synchronize the local date and time with a reference server. The server will miscalculate the offset reply, if it receives a request from an NTP client containing a date that is more or less than 34 years of the server's date.

This offset is a 64-bit value, with 32 bits representing whole seconds, and 32 bits representing fractions of a second . The 34-year limit is imposed by the use of a 32-bit signed integer.

The NTP server performs a series of calculations, accounting for transmission delay and computing time, resulting in a value which represents the difference between the NTP server time and the requesting machine's time.

The packet sent back to the client is a date/time offset, which is then used to update the client's date/time.


Clients making requests of an NTP server and supplying a date/time that is more than 34 years in the future (or past) from the NTP server date/time will receive an incorrect date/time offset from the server, resulting in an incorrect date/time on the client.

There is no known impact to the NTP server.


NTPd Version 4 resolves this issue.

Vendor Information

584606 Affected

Updated:  March 05, 2004



Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

CVSS Metrics

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Thanks to David L. Mills of for reporting this vulnerability.

This document was written by Robert D Hanson.

Other Information

CVE IDs: None
Severity Metric: 0.06
Date Public: 2004-01-22
Date First Published: 2004-03-05
Date Last Updated: 2004-03-05 19:06 UTC
Document Revision: 7

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