mod_reqtimeout could be a reason, since it has been activated according to apt-listchanges:
apache2 (2.2.15-1) unstable; urgency=low
* This release adds and enables mod_reqtimeout, which limits the time
Apache waits for a client to send a complete request. This helps to
mitigate against certain denial of service attacks. In case of problems
with slow clients, the timeout values can be adjusted in
/etc/apache2/mods-available/reqtimeout.conf , or the module can be
disabled with "a2dismod reqtimeout".
mod_reqtimeout could be a reason, since it has been activated according to apt-listchanges:
apache2 (2.2.15-1) unstable; urgency=low
* This release adds and enables mod_reqtimeout, which limits the time apache2/ mods-available/ reqtimeout. conf , or the module can be
Apache waits for a client to send a complete request. This helps to
mitigate against certain denial of service attacks. In case of problems
with slow clients, the timeout values can be adjusted in
/etc/
disabled with "a2dismod reqtimeout".
-- Chuck Short <email address hidden> Tue, 13 Apr 2010 09:09:34 -0400
I have now disabled it and will audit the server logs whether the error has gone.