<s>
In	O
HTTP	B-Protocol
networking	B-Architecture
,	O
typically	O
on	O
the	O
World	O
Wide	O
Web	O
,	O
referer	B-Protocol
spoofing	I-Protocol
(	O
based	O
on	O
a	O
canonised	O
misspelling	O
of	O
"	O
referrer	B-Protocol
"	O
)	O
sends	O
incorrect	O
referer	B-Protocol
information	O
in	O
an	O
HTTP	B-Protocol
request	O
in	O
order	O
to	O
prevent	O
a	O
website	O
from	O
obtaining	O
accurate	O
data	O
on	O
the	O
identity	O
of	O
the	O
web	O
page	O
previously	O
visited	O
by	O
the	O
user	O
.	O
</s>
<s>
Referer	B-Protocol
spoofing	I-Protocol
is	O
typically	O
done	O
for	O
data	O
privacy	O
reasons	O
,	O
in	O
testing	O
,	O
or	O
in	O
order	O
to	O
request	O
information	O
(	O
without	O
genuine	O
authority	O
)	O
which	O
some	O
web	B-Application
servers	I-Application
may	O
only	O
supply	O
in	O
response	O
to	O
requests	O
with	O
specific	O
HTTP	B-Protocol
referers	I-Protocol
.	O
</s>
<s>
To	O
improve	O
their	O
privacy	O
,	O
individual	O
browser	B-Application
users	O
may	O
replace	O
accurate	O
referer	B-Protocol
data	O
with	O
inaccurate	O
data	O
,	O
though	O
many	O
simply	O
suppress	O
their	O
browser	B-Application
's	O
sending	O
of	O
any	O
referer	B-Protocol
data	O
.	O
</s>
<s>
Sending	O
no	O
referrer	B-Protocol
information	O
is	O
not	O
technically	O
spoofing	O
,	O
though	O
sometimes	O
also	O
described	O
as	O
such	O
.	O
</s>
<s>
In	O
software	O
,	O
systems	O
and	O
networks	O
testing	O
,	O
and	O
sometimes	O
penetration	O
testing	O
,	O
referer	B-Protocol
spoofing	I-Protocol
is	O
often	O
just	O
part	O
of	O
a	O
larger	O
procedure	O
of	O
transmitting	O
both	O
accurate	O
and	O
inaccurate	O
as	O
well	O
as	O
expected	O
and	O
unexpected	O
input	O
to	O
the	O
HTTPD	O
system	O
being	O
tested	O
and	O
observing	O
the	O
results	O
.	O
</s>
<s>
While	O
many	O
websites	O
are	O
configured	O
to	O
gather	O
referer	B-Protocol
information	O
and	O
serve	O
different	O
content	O
depending	O
on	O
the	O
referer	B-Protocol
information	O
obtained	O
,	O
exclusively	O
relying	O
on	O
HTTP	B-Protocol
referer	I-Protocol
information	O
for	O
authentication	O
and	O
authorization	O
purposes	O
is	O
not	O
a	O
genuine	O
computer	O
security	O
measure	O
.	O
</s>
<s>
HTTP	B-Protocol
referer	I-Protocol
information	O
is	O
freely	O
alterable	O
and	O
interceptable	O
,	O
and	O
is	O
not	O
a	O
password	O
,	O
though	O
some	O
poorly	O
configured	O
systems	O
treat	O
it	O
as	O
such	O
.	O
</s>
<s>
Some	O
websites	O
,	O
especially	O
many	O
image	O
hosting	O
sites	O
,	O
use	O
referer	B-Protocol
information	O
to	O
secure	O
their	O
materials	O
:	O
only	O
browsers	B-Application
arriving	O
from	O
their	O
web	O
pages	O
are	O
served	O
images	O
.	O
</s>
<s>
Additionally	O
a	O
site	O
may	O
want	O
users	O
to	O
click	O
through	O
pages	O
with	O
advertisements	O
before	O
directly	O
being	O
able	O
to	O
access	O
a	O
downloadable	O
file	O
–	O
using	O
the	O
referring	B-Protocol
page	I-Protocol
or	O
referring	O
site	O
information	O
can	O
help	O
a	O
site	O
redirect	O
unauthorized	O
users	O
to	O
the	O
landing	O
page	O
the	O
site	O
would	O
like	O
to	O
use	O
.	O
</s>
<s>
If	O
attackers	O
acquire	O
knowledge	O
of	O
these	O
approved	O
referrers	B-Protocol
,	O
which	O
is	O
often	O
trivial	O
because	O
many	O
sites	O
follow	O
a	O
common	O
template	O
,	O
they	O
can	O
use	O
that	O
information	O
combined	O
with	O
this	O
to	O
exploit	O
and	O
gain	O
access	O
to	O
the	O
materials	O
.	O
</s>
<s>
Spoofing	O
often	O
allows	O
access	O
to	O
a	O
site	O
's	O
content	O
where	O
the	O
site	O
's	O
web	B-Application
server	I-Application
is	O
configured	O
to	O
block	O
browsers	B-Application
that	O
do	O
not	O
send	O
referer	B-Protocol
headers	I-Protocol
.	O
</s>
<s>
It	O
can	O
also	O
be	O
used	O
to	O
defeat	O
referer	B-Protocol
checking	O
controls	O
that	O
are	O
used	O
to	O
mitigate	O
Cross-Site	B-Protocol
Request	I-Protocol
Forgery	I-Protocol
attacks	O
.	O
</s>
<s>
Several	O
software	O
tools	O
exist	O
to	O
facilitate	O
referer	B-Protocol
spoofing	I-Protocol
in	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
Some	O
are	O
extensions	O
to	O
popular	O
browsers	B-Application
such	O
as	O
Mozilla	B-Application
Firefox	I-Application
or	O
Internet	B-Application
Explorer	I-Application
,	O
which	O
may	O
provide	O
facilities	O
to	O
customise	O
and	O
manage	O
referrer	B-Protocol
URLs	O
for	O
each	O
website	O
the	O
user	O
visits	O
.	O
</s>
<s>
Other	O
tools	O
include	O
proxy	B-Application
servers	I-Application
,	O
to	O
which	O
an	O
individual	O
configures	O
their	O
browser	B-Application
to	O
send	O
all	O
HTTP	B-Protocol
requests	I-Protocol
.	O
</s>
<s>
The	O
proxy	O
then	O
forwards	O
different	O
headers	O
to	O
the	O
intended	O
website	O
,	O
usually	O
removing	O
or	O
modifying	O
the	O
referer	B-Protocol
header	I-Protocol
.	O
</s>
<s>
Such	O
proxies	O
may	O
also	O
present	O
privacy	O
issues	O
for	O
users	O
,	O
as	O
they	O
may	O
log	B-Application
the	O
user	O
's	O
activity	O
.	O
</s>
