Summary
The remote host implements TCP timestamps and therefore allows to compute the uptime.
Impact
A side effect of this feature is that the uptime of the remote host can sometimes be computed.
Solution
To disable TCP timestamps on linux add the line 'net.ipv4.tcp_timestamps = 0' to /etc/sysctl.conf. Execute 'sysctl -p' to apply the settings at runtime.
To disable TCP timestamps on Windows execute 'netsh int tcp set global timestamps=disabled'
Starting with Windows Server 2008 and Vista, the timestamp can not be completely disabled.
The default behavior of the TCP/IP stack on this Systems is, to not use the Timestamp options when initiating TCP connections, but use them if the TCP peer that is initiating communication includes them in their synchronize (SYN) segment.
See also: http://www.microsoft.com/en-us/download/details.aspx?id=9152
Insight
The remote host implements TCP timestamps, as defined by RFC1323.
Affected
TCP/IPv4 implementations that implement RFC1323.
Detection
Special IP packets are forged and sent with a little delay in between to the target IP. The responses are searched for a timestamps. If found, the timestamps are reported.
References
Updated on 2015-03-25
