<s>
When	O
a	O
web	B-Application
browser	I-Application
attempts	O
to	O
open	O
a	O
URL	O
that	O
has	O
been	O
redirected	O
,	O
a	O
page	O
with	O
a	O
different	O
URL	O
is	O
opened	O
.	O
</s>
<s>
A	O
website	O
may	O
potentially	O
be	O
accessible	O
over	O
both	O
a	O
secure	O
HTTPS	B-Protocol
URI	O
scheme	O
and	O
plain	O
HTTP	B-Protocol
(	O
an	O
insecure	O
URI	O
beginning	O
with	O
""	O
)	O
.	O
</s>
<s>
If	O
a	O
user	O
types	O
in	O
a	O
URI	O
or	O
clicks	O
on	O
a	O
link	O
that	O
refers	O
to	O
the	O
insecure	O
variant	O
,	O
the	O
browser	B-Application
will	O
automatically	O
redirect	O
to	O
the	O
secure	O
version	O
in	O
case	O
the	O
website	O
is	O
contained	O
in	O
the	O
HSTS	B-Protocol
preload	O
list	O
shipped	O
with	O
the	O
application	O
or	O
if	O
the	O
user	O
had	O
already	O
visited	O
the	O
origin	O
in	O
the	O
past	O
.	O
</s>
<s>
Otherwise	O
the	O
website	O
will	O
be	O
contacted	O
over	O
HTTP	B-Protocol
.	I-Protocol
</s>
<s>
A	O
website	O
operator	O
may	O
decide	O
to	O
serve	O
such	O
requests	O
by	O
redirecting	O
the	O
browser	B-Application
to	O
the	O
HTTPS	B-Protocol
variant	O
instead	O
and	O
hopefully	O
also	O
priming	O
HSTS	B-Protocol
for	O
future	O
accesses	O
.	O
</s>
<s>
These	O
links	O
might	O
be	O
from	O
other	O
sites	O
that	O
have	O
not	O
realized	O
that	O
there	O
is	O
a	O
change	O
or	O
from	O
bookmarks/favorites	O
that	O
users	O
have	O
saved	O
in	O
their	O
browsers	B-Application
.	O
</s>
<s>
The	O
same	O
applies	O
to	O
search	B-Application
engines	I-Application
.	O
</s>
<s>
By	O
using	O
a	O
"	O
moved	B-Protocol
permanently	I-Protocol
"	O
redirect	O
to	O
the	O
new	O
URL	O
,	O
visitors	O
will	O
still	O
end	O
up	O
at	O
the	O
correct	O
page	O
.	O
</s>
<s>
Also	O
,	O
in	O
the	O
next	O
search	B-Application
engine	I-Application
pass	O
,	O
the	O
search	B-Application
engine	I-Application
should	O
detect	O
and	O
use	O
the	O
newer	O
URL	O
.	O
</s>
<s>
The	O
access	O
logs	B-Application
of	O
most	O
web	O
servers	O
keep	O
detailed	O
information	O
about	O
where	O
visitors	O
came	O
from	O
and	O
how	O
they	O
browsed	O
the	O
hosted	O
site	O
.	O
</s>
<s>
This	O
is	O
because	O
the	O
visitor	O
's	O
browser	B-Application
has	O
no	O
need	O
to	O
communicate	O
with	O
the	O
original	O
server	O
when	O
the	O
visitor	O
clicks	O
on	O
an	O
outgoing	O
link	O
.	O
</s>
<s>
As	O
this	O
added	O
request	O
will	O
leave	O
a	O
trace	O
in	O
the	O
server	B-Application
log	I-Application
,	O
revealing	O
exactly	O
which	O
link	O
was	O
followed	O
,	O
it	O
can	O
also	O
be	O
a	O
privacy	O
issue	O
.	O
</s>
<s>
This	O
practice	O
results	O
in	O
a	O
URL	O
that	O
is	O
aesthetically	O
unpleasant	O
and	O
difficult	O
to	O
remember	O
,	O
and	O
which	O
may	O
not	O
fit	O
within	O
the	O
size	O
limitations	O
of	O
microblogging	B-Application
sites	O
.	O
</s>
<s>
Post/Redirect/Get	O
(	O
PRG	O
)	O
is	O
a	O
web	O
development	O
design	O
pattern	O
that	O
prevents	O
some	O
duplicate	O
form	B-General_Concept
submissions	O
if	O
the	O
user	O
clicks	O
the	O
refresh	O
button	O
after	O
submitting	O
the	O
form	B-General_Concept
,	O
creating	O
a	O
more	O
intuitive	O
interface	O
for	O
user	B-Protocol
agents	I-Protocol
(	O
users	O
)	O
.	O
</s>
<s>
There	O
are	O
two	O
approaches	O
to	O
serve	O
mobile	O
users	O
:	O
Make	O
the	O
website	O
responsive	B-General_Concept
or	O
redirect	O
to	O
a	O
mobile	O
website	O
version	O
.	O
</s>
<s>
Redirects	O
have	O
been	O
used	O
to	O
manipulate	O
search	B-Application
engines	I-Application
with	O
unethical	O
intentions	O
,	O
e.g.	O
,	O
URL	B-Protocol
hijacking	I-Protocol
.	O
</s>
<s>
URL	B-Protocol
hijacking	I-Protocol
is	O
an	O
off-domain	O
redirect	O
technique	O
that	O
exploited	O
the	O
nature	O
of	O
the	O
search	B-Application
engine	I-Application
's	O
handling	O
for	O
temporary	O
redirects	O
.	O
</s>
<s>
If	O
a	O
temporary	O
redirect	O
is	O
encountered	O
,	O
search	B-Application
engines	I-Application
have	O
to	O
decide	O
whether	O
they	O
assign	O
the	O
ranking	O
value	O
to	O
the	O
URL	O
that	O
initializes	O
the	O
redirect	O
or	O
to	O
the	O
redirect	O
target	O
URL	O
.	O
</s>
<s>
The	O
URL	O
that	O
initiates	O
the	O
redirect	O
may	O
be	O
kept	O
to	O
show	O
up	O
in	O
search	B-Application
results	I-Application
,	O
as	O
the	O
redirect	O
indicates	O
a	O
temporary	O
nature	O
.	O
</s>
<s>
Under	O
certain	O
circumstances	O
it	O
was	O
possible	O
to	O
exploit	O
this	O
behavior	O
by	O
applying	O
temporary	O
redirects	O
to	O
well-ranking	O
URLs	O
,	O
leading	O
to	O
a	O
replacement	O
of	O
the	O
original	O
URL	O
in	O
search	B-Application
results	I-Application
by	O
the	O
URL	O
that	O
initialized	O
the	O
redirect	O
,	O
therefore	O
"	O
stealing	O
"	O
the	O
ranking	O
.	O
</s>
<s>
This	O
method	O
was	O
usually	O
combined	O
with	O
sneaky	O
redirects	O
to	O
re-target	O
the	O
user	O
stream	O
from	O
the	O
search	B-Application
results	I-Application
to	O
a	O
target	O
page	O
.	O
</s>
<s>
Search	B-Application
engines	I-Application
have	O
developed	O
efficient	O
technologies	O
to	O
detect	O
these	O
kinds	O
of	O
manipulative	O
approaches	O
.	O
</s>
<s>
Major	O
search	B-Application
engines	I-Application
usually	O
apply	O
harsh	O
ranking	O
penalties	O
on	O
sites	O
that	O
get	O
caught	O
applying	O
techniques	O
like	O
these	O
.	O
</s>
<s>
Because	O
modern	O
browsers	B-Application
always	O
show	O
the	O
real	O
URL	O
in	O
the	O
address	O
bar	O
,	O
the	O
threat	O
is	O
lessened	O
.	O
</s>
<s>
When	O
a	O
link	O
is	O
clicked	O
,	O
the	O
browser	B-Application
sends	O
along	O
in	O
the	O
HTTP	B-Protocol
request	O
a	O
field	O
called	O
referer	B-Protocol
which	O
indicates	O
the	O
source	O
of	O
the	O
link	O
.	O
</s>
<s>
This	O
field	O
is	O
populated	O
with	O
the	O
URL	O
of	O
the	O
current	O
web	O
page	O
,	O
and	O
will	O
end	O
up	O
in	O
the	O
logs	B-Application
of	O
the	O
server	O
serving	O
the	O
external	O
link	O
.	O
</s>
<s>
Since	O
sensitive	O
pages	O
may	O
have	O
sensitive	O
URLs	O
(	O
for	O
example	O
,	O
https://company.com/plans-for-the-next-release-of-our-product	O
)	O
,	O
it	O
is	O
not	O
desirable	O
for	O
the	O
referrer	B-Protocol
URL	O
to	O
leave	O
the	O
organization	O
.	O
</s>
<s>
A	O
redirection	O
page	O
that	O
performs	O
referrer	B-Protocol
hiding	O
could	O
be	O
embedded	O
in	O
all	O
external	O
URLs	O
,	O
transforming	O
for	O
example	O
https://externalsite.com/page	O
into	O
https://redirect.company.com/https://externalsite.com/page	O
.	O
</s>
<s>
This	O
technique	O
also	O
eliminates	O
other	O
potentially	O
sensitive	O
information	O
from	O
the	O
referrer	B-Protocol
URL	O
,	O
such	O
as	O
the	O
session	B-Protocol
ID	I-Protocol
,	O
and	O
can	O
reduce	O
the	O
chance	O
of	O
phishing	O
by	O
indicating	O
to	O
the	O
end	O
user	O
that	O
they	O
passed	O
a	O
clear	O
gateway	O
to	O
another	O
site	O
.	O
</s>
<s>
Several	O
different	O
kinds	O
of	O
response	O
to	O
the	O
browser	B-Application
will	O
result	O
in	O
a	O
redirection	O
.	O
</s>
<s>
These	O
vary	O
in	O
whether	O
they	O
affect	O
HTTP	B-Protocol
headers	I-Protocol
or	O
HTML	O
content	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
web	O
author	O
with	O
no	O
control	O
over	O
the	O
headers	O
might	O
use	O
a	O
Refresh	B-Protocol
meta	I-Protocol
tag	I-Protocol
whereas	O
a	O
web	O
server	O
administrator	O
redirecting	O
all	O
pages	O
on	O
a	O
site	O
is	O
more	O
likely	O
to	O
use	O
server	O
configuration	O
.	O
</s>
<s>
This	O
method	O
is	O
often	O
used	O
as	O
a	O
fall-back	O
—	O
if	O
the	O
browser	B-Application
does	O
not	O
support	O
the	O
automatic	O
redirect	O
,	O
the	O
visitor	O
can	O
still	O
reach	O
the	O
target	O
document	O
by	O
following	O
the	O
link	O
.	O
</s>
<s>
In	O
the	O
HTTP	B-Protocol
protocol	I-Protocol
used	O
by	O
the	O
World	O
Wide	O
Web	O
,	O
a	O
redirect	O
is	O
a	O
response	O
with	O
a	O
status	B-Protocol
code	I-Protocol
beginning	O
with	O
3	O
that	O
causes	O
a	O
browser	B-Application
to	O
display	O
a	O
different	O
page	O
.	O
</s>
<s>
HTTP/1.1	B-Protocol
defines	O
several	O
status	O
codes	O
for	O
redirection	O
(	O
RFC	O
7231	O
)	O
:	O
</s>
<s>
300	B-Protocol
multiple	I-Protocol
choices	I-Protocol
(	O
e.g.	O
</s>
<s>
Status	O
codes	O
304	B-Protocol
not	I-Protocol
modified	I-Protocol
and	O
305	B-Protocol
use	I-Protocol
proxy	I-Protocol
are	O
not	O
redirects	O
.	O
</s>
<s>
All	O
of	O
these	O
status	O
codes	O
require	O
the	O
URL	O
of	O
the	O
redirect	O
target	O
to	O
be	O
given	O
in	O
the	O
Location	O
:	O
header	O
of	O
the	O
HTTP	B-Protocol
response	O
.	O
</s>
<s>
The	O
300	B-Protocol
multiple	I-Protocol
choices	I-Protocol
will	O
usually	O
list	O
all	O
choices	O
in	O
the	O
body	O
of	O
the	O
message	O
and	O
show	O
the	O
default	O
choice	O
in	O
the	O
Location	O
:	O
header	O
.	O
</s>
<s>
A	O
HTTP	B-Protocol
response	O
with	O
the	O
301	O
"	O
moved	B-Protocol
permanently	I-Protocol
"	O
redirect	O
looks	O
like	O
this	O
:	O
</s>
<s>
Web	O
authors	O
producing	O
HTML	O
content	O
ca	O
n't	O
usually	O
create	O
redirects	O
using	O
HTTP	B-Protocol
headers	I-Protocol
as	O
these	O
are	O
generated	O
automatically	O
by	O
the	O
web	O
server	O
program	O
when	O
serving	O
an	O
HTML	O
file	O
.	O
</s>
<s>
The	O
same	O
is	O
usually	O
true	O
even	O
for	O
programmers	O
writing	O
CGI	B-Language
scripts	I-Language
,	O
though	O
some	O
servers	O
allow	O
scripts	O
to	O
add	O
custom	O
headers	O
(	O
e.g.	O
</s>
<s>
Many	O
web	O
servers	O
will	O
generate	O
a	O
3xx	O
status	B-Protocol
code	I-Protocol
if	O
a	O
script	O
outputs	O
a	O
"	O
Location	O
:	O
"	O
header	O
line	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
PHP	B-Application
,	O
one	O
can	O
use	O
the	O
"	O
header	O
"	O
function	O
:	O
</s>
<s>
In	O
the	O
ASP	B-General_Concept
scripting	I-General_Concept
language	O
,	O
this	O
can	O
also	O
be	O
accomplished	O
using	O
response.buffer	O
=	O
true	O
and	O
response.redirect	O
"	O
https://www.example.com/	O
"	O
HTTP/1.1	B-Protocol
allows	O
for	O
either	O
a	O
relative	O
URI	O
reference	O
or	O
an	O
absolute	O
URI	O
reference	O
.	O
</s>
<s>
The	O
Apache	B-Application
HTTP	I-Application
Server	I-Application
mod_alias	O
extension	O
can	O
be	O
used	O
to	O
redirect	O
certain	O
requests	O
.	O
</s>
<s>
For	O
more	O
flexible	O
URL	B-Protocol
rewriting	I-Protocol
and	O
redirection	O
,	O
Apache	B-Application
mod_rewrite	O
can	O
be	O
used	O
.	O
</s>
<s>
Such	O
configuration	O
can	O
be	O
applied	O
to	O
one	O
or	O
all	O
sites	O
on	O
the	O
server	O
through	O
the	O
server	O
configuration	O
files	O
or	O
to	O
a	O
single	O
content	O
directory	O
through	O
a	O
.htaccess	B-Protocol
file	O
.	O
</s>
<s>
Nginx	B-Operating_System
has	O
an	O
integrated	O
http	B-Protocol
rewrite	O
module	O
,	O
which	O
can	O
be	O
used	O
to	O
perform	O
advanced	O
URL	O
processing	O
and	O
even	O
web-page	O
generation	O
(	O
with	O
the	O
return	O
directive	O
)	O
.	O
</s>
<s>
A	O
showing	O
example	O
of	O
such	O
advanced	O
use	O
of	O
the	O
rewrite	O
module	O
is	O
,	O
which	O
implements	O
a	O
deterministic	O
URL	O
shortening	O
service	O
entirely	O
with	O
the	O
help	O
of	O
nginx	B-Operating_System
configuration	O
language	O
alone	O
.	O
</s>
<s>
For	O
example	O
,	O
if	O
a	O
request	O
for	O
/DragonFlyBSD/HAMMER.5	O
were	O
to	O
come	O
along	O
,	O
it	O
would	O
first	O
be	O
redirected	O
internally	O
to	O
/d/HAMMER.5	O
with	O
the	O
first	O
rewrite	O
directive	O
below	O
(	O
only	O
affecting	O
the	O
internal	O
state	O
,	O
without	O
any	O
HTTP	B-Protocol
replies	O
issued	O
to	O
the	O
client	O
just	O
yet	O
)	O
,	O
and	O
then	O
with	O
the	O
second	O
rewrite	O
directive	O
,	O
an	O
HTTP	B-Protocol
response	O
with	O
a	O
302	B-Protocol
Found	I-Protocol
status	I-Protocol
code	I-Protocol
would	O
be	O
issued	O
to	O
the	O
client	O
to	O
actually	O
redirect	O
to	O
the	O
external	O
cgi	B-Language
script	I-Language
of	O
web-man	O
:	O
</s>
<s>
Netscape	B-Protocol
introduced	O
the	O
meta	B-Protocol
refresh	I-Protocol
feature	O
which	O
refreshes	O
a	O
page	O
after	O
a	O
certain	O
amount	O
of	O
time	O
.	O
</s>
<s>
This	O
is	O
supported	O
by	O
most	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
The	O
anchor	O
in	O
the	O
"	O
body	O
"	O
section	O
is	O
for	O
users	O
whose	O
browsers	B-Application
do	O
not	O
support	O
this	O
feature	O
.	O
</s>
<s>
The	O
same	O
effect	O
can	O
be	O
achieved	O
with	O
an	O
HTTP	B-Protocol
refresh	I-Protocol
header	O
:	O
</s>
<s>
This	O
response	O
is	O
easier	O
to	O
generate	O
by	O
CGI	O
programs	O
because	O
one	O
does	O
not	O
need	O
to	O
change	O
the	O
default	O
status	B-Protocol
code	I-Protocol
.	O
</s>
<s>
Note	O
:	O
Usually	O
,	O
the	O
HTTP	B-Protocol
server	O
adds	O
the	O
status	O
line	O
and	O
the	O
Content-Length	O
header	O
automatically	O
.	O
</s>
<s>
The	O
W3C	O
discourage	O
the	O
use	O
of	O
meta	B-Protocol
refresh	I-Protocol
,	O
since	O
it	O
does	O
not	O
communicate	O
any	O
information	O
about	O
either	O
the	O
original	O
or	O
new	O
resource	O
,	O
to	O
the	O
browser	B-Application
(	O
or	O
search	B-Application
engine	I-Application
)	O
.	O
</s>
<s>
The	O
W3C	O
's	O
Web	O
Content	O
Accessibility	O
Guidelines	O
(	O
7.4	O
)	O
discourage	O
the	O
creation	O
of	O
auto-refreshing	O
pages	O
,	O
since	O
most	O
web	B-Application
browsers	I-Application
do	O
not	O
allow	O
the	O
user	O
to	O
disable	O
or	O
control	O
the	O
refresh	O
rate	O
.	O
</s>
<s>
JavaScript	B-Language
can	O
cause	O
a	O
redirect	O
by	O
setting	O
the	O
window.location	O
attribute	O
,	O
e.g.	O
</s>
<s>
Normally	O
JavaScript	B-Language
pushes	O
the	O
redirector	O
site	O
's	O
URL	O
to	O
the	O
browser	B-Application
's	O
history	O
.	O
</s>
<s>
However	O
,	O
HTTP	B-Protocol
headers	I-Protocol
or	O
the	O
refresh	B-Protocol
meta	I-Protocol
tag	I-Protocol
may	O
be	O
preferred	O
for	O
security	O
reasons	O
and	O
because	O
JavaScript	B-Language
will	O
not	O
be	O
executed	O
by	O
some	O
browsers	B-Application
and	O
many	O
web	B-Application
crawlers	I-Application
.	O
</s>
<s>
A	O
slightly	O
different	O
effect	O
can	O
be	O
achieved	O
by	O
creating	O
an	O
inline	O
frame	B-General_Concept
:	O
</s>
<s>
One	O
main	O
difference	O
to	O
the	O
above	O
redirect	O
methods	O
is	O
that	O
for	O
a	O
frame	B-General_Concept
redirect	O
,	O
the	O
browser	B-Application
displays	O
the	O
URL	O
of	O
the	O
frame	B-General_Concept
document	O
and	O
not	O
the	O
URL	O
of	O
the	O
target	O
page	O
in	O
the	O
URL	O
bar	O
.	O
</s>
<s>
Before	O
HTML5	O
,	O
the	O
same	O
effect	O
could	O
be	O
done	O
with	O
an	O
HTML	B-General_Concept
frame	I-General_Concept
that	O
contains	O
the	O
target	O
page	O
:	O
</s>
<s>
This	O
is	O
unavoidable	O
if	O
the	O
different	O
links	O
in	O
the	O
chain	O
are	O
served	O
by	O
different	O
servers	O
though	O
it	O
should	O
be	O
minimised	O
by	O
rewriting	O
the	O
URL	O
as	O
much	O
as	O
possible	O
on	O
the	O
server	O
before	O
returning	O
it	O
to	O
the	O
browser	B-Application
as	O
a	O
redirect	O
.	O
</s>
<s>
Browsers	B-Application
should	O
stop	O
redirecting	O
after	O
a	O
certain	O
number	O
of	O
hops	O
and	O
display	O
an	O
error	O
message	O
.	O
</s>
<s>
The	O
HTTP/1.1	B-Protocol
Standard	O
states	O
:	O
</s>
<s>
A	O
redirecting	O
link	O
can	O
also	O
be	O
used	O
as	O
a	O
permanent	O
address	O
for	O
content	O
that	O
frequently	O
changes	O
hosts	O
,	O
similarly	O
to	O
the	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
.	O
</s>
<s>
Recently	O
,	O
URL	O
redirection	O
services	O
have	O
taken	O
to	O
using	O
AJAX	B-Device
as	O
an	O
efficient	O
,	O
user	O
friendly	O
method	O
for	O
creating	O
shortened	O
URLs	O
.	O
</s>
<s>
A	O
major	O
drawback	O
of	O
some	O
URL	O
redirection	O
services	O
is	O
the	O
use	O
of	O
delay	O
pages	O
,	O
or	O
frame	B-General_Concept
based	O
advertising	O
,	O
to	O
generate	O
revenue	O
.	O
</s>
<s>
The	O
first	O
redirect	O
services	O
took	O
advantage	O
of	O
top-level	O
domains	O
(	O
TLD	O
)	O
such	O
as	O
"	O
.to	B-Protocol
"	O
(	O
Tonga	O
)	O
,	O
"	O
.at	B-General_Concept
"	O
(	O
Austria	O
)	O
and	O
"	O
.is	B-Application
"	O
(	O
Iceland	O
)	O
.	O
</s>
<s>
With	O
the	O
launch	O
of	O
TinyURL	B-Protocol
in	O
2002	O
a	O
new	O
kind	O
of	O
redirecting	O
service	O
was	O
born	O
,	O
namely	O
URL	O
shortening	O
.	O
</s>
<s>
Since	O
2006	O
,	O
with	O
the	O
140	O
character	O
limit	O
on	O
the	O
extremely	O
popular	O
Twitter	B-Application
service	O
,	O
these	O
short	O
URL	O
services	O
have	O
been	O
heavily	O
used	O
.	O
</s>
<s>
Redirection	O
services	O
can	O
hide	O
the	O
referrer	B-Protocol
by	O
placing	O
an	O
intermediate	O
page	O
between	O
the	O
page	O
the	O
link	O
is	O
on	O
and	O
its	O
destination	O
.	O
</s>
<s>
Although	O
these	O
are	O
conceptually	O
similar	O
to	O
other	O
URL	O
redirection	O
services	O
,	O
they	O
serve	O
a	O
different	O
purpose	O
,	O
and	O
they	O
rarely	O
attempt	O
to	O
shorten	O
or	O
obfuscate	O
the	O
destination	O
URL	O
(	O
as	O
their	O
only	O
intended	O
side-effect	O
is	O
to	O
hide	O
referrer	B-Protocol
information	O
and	O
provide	O
a	O
clear	O
gateway	O
between	O
other	O
websites	O
.	O
)	O
</s>
<s>
This	O
type	O
of	O
redirection	O
is	O
often	O
used	O
to	O
prevent	O
potentially-malicious	O
links	O
from	O
gaining	O
information	O
using	O
the	O
referrer	B-Protocol
,	O
for	O
example	O
a	O
session	B-Protocol
ID	I-Protocol
in	O
the	O
query	O
string	O
.	O
</s>
<s>
Here	O
is	O
a	O
simplistic	O
example	O
of	O
such	O
a	O
service	O
,	O
written	O
in	O
PHP	B-Application
.	O
</s>
<s>
by	O
referrer	B-Protocol
,	O
although	O
that	O
could	O
be	O
spoofed	O
)	O
.	O
</s>
<s>
URL	O
redirection	O
can	O
be	O
abused	O
by	O
attackers	O
for	O
phishing	O
attacks	O
,	O
such	O
as	O
open	B-Protocol
redirect	I-Protocol
and	O
covert	O
redirect	O
.	O
</s>
<s>
"	O
An	O
open	B-Protocol
redirect	I-Protocol
is	O
an	O
application	O
that	O
takes	O
a	O
parameter	O
and	O
redirects	O
a	O
user	O
to	O
the	O
parameter	O
value	O
without	O
any	O
validation.	O
"	O
</s>
