I just found out about this problem too. The page is rendered correctly with Firefox 47 on Linux. It fails with Chromium and Konqueror on Linux. It fails with Firefox, Chrome and Opera on Windows.
The buffer overflow occurs when status.cgi tries to display the status message returned by NTP: NTP OK: Décalage -0,01155954599 secs The message obviously contains an accent. How does Firefox on Linux succeed when all the others fail? It is due to the Accepted-Language header. Firefox send: "en-US,en;q=0.8,fr- BE;q=0.5,fr;q=0.3" when Chromium, for instance, send "en- US,en;q=0.8,fr;q=0.6". If I replace "fr" by "fr-BE" in the Chromium header, it succeeds. If I replace it with "fr-FR" (the locale is not defined on the nagios server), the buffer overflow occurs and the status page is truncated. The problem is not with an accent I inserted in a configuration file. I can't apply the suggestion from Christian Erpelding (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=792787#10) as I have no control over the string returned by the NTP plugin. It occurs with nagios3 3.5.1.dfsg-2+b1.