<s>
JSONP	B-General_Concept
,	O
or	O
JSON-P	B-General_Concept
(	O
JSON	B-General_Concept
with	I-General_Concept
Padding	I-General_Concept
)	O
,	O
is	O
a	O
historical	O
JavaScript	O
technique	O
for	O
requesting	O
data	O
by	O
loading	O
a	O
element	O
,	O
which	O
is	O
an	O
element	O
intended	O
to	O
load	O
ordinary	O
JavaScript	O
.	O
</s>
<s>
JSONP	B-General_Concept
enables	O
sharing	O
of	O
data	O
bypassing	O
same-origin	B-Protocol
policy	I-Protocol
,	O
which	O
disallows	O
running	O
JavaScript	O
code	O
to	O
read	O
media	O
DOM	O
elements	O
or	O
XMLHttpRequest	O
data	O
fetched	O
from	O
outside	O
the	O
page	O
's	O
originating	O
site	O
.	O
</s>
<s>
JSONP	B-General_Concept
is	O
vulnerable	O
to	O
the	O
data	O
source	O
replacing	O
the	O
innocuous	O
function	O
call	O
with	O
malicious	O
code	O
,	O
which	O
is	O
why	O
it	O
has	O
been	O
superseded	O
by	O
cross-origin	B-General_Concept
resource	I-General_Concept
sharing	I-General_Concept
(	O
available	O
since	O
2009	O
)	O
in	O
modern	O
applications	O
.	O
</s>
<s>
Services	O
replying	O
with	O
pure	O
JSON	B-General_Concept
data	O
,	O
however	O
,	O
were	O
not	O
able	O
to	O
share	O
data	O
from	O
foreign	O
origins	O
before	O
the	O
adoption	O
of	O
CORS	B-General_Concept
(	O
Cross-origin	B-General_Concept
resource	I-General_Concept
sharing	I-General_Concept
)	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
request	O
to	O
a	O
foreign	O
service	O
http://server.example.com/Users/1234	O
may	O
return	O
a	O
record	O
for	O
a	O
person	O
named	O
Clem	O
in	O
the	O
JSON	B-General_Concept
format	O
.	O
</s>
<s>
JSON	B-General_Concept
syntax	O
is	O
consistent	O
with	O
JavaScript	O
's	O
object	O
syntax	O
.	O
</s>
<s>
Without	O
support	O
for	O
CORS	B-General_Concept
,	O
an	O
attempt	O
to	O
use	O
the	O
data	O
across	O
domains	O
results	O
in	O
a	O
JavaScript	O
error	O
.	O
</s>
<s>
The	O
browser	O
will	O
download	O
the	O
<script>	O
file	O
,	O
evaluate	O
its	O
contents	O
,	O
misinterpret	O
the	O
raw	O
JSON	B-General_Concept
data	O
as	O
a	O
block	O
,	O
and	O
throw	O
a	O
syntax	O
error	O
.	O
</s>
<s>
In	O
the	O
JSONP	B-General_Concept
usage	O
pattern	O
,	O
the	O
URL	O
request	O
pointed	O
to	O
by	O
the	O
src	O
attribute	O
in	O
the	O
<script>	O
element	O
returns	O
JSON	B-General_Concept
data	O
,	O
with	O
JavaScript	O
code	O
(	O
usually	O
a	O
function	O
call	O
)	O
wrapped	O
around	O
it	O
.	O
</s>
<s>
In	O
this	O
way	O
,	O
a	O
function	O
that	O
is	O
already	O
defined	O
in	O
the	O
JavaScript	O
environment	O
can	O
manipulate	O
the	O
JSON	B-General_Concept
data	O
.	O
</s>
<s>
A	O
typical	O
JSONP	B-General_Concept
request	O
and	O
response	O
are	O
shown	O
below	O
.	O
</s>
<s>
The	O
function	O
call	O
to	O
parseResponse( )	O
is	O
the	O
"	O
P	O
"	O
of	O
JSONP	B-General_Concept
—	O
the	O
"	O
padding	O
"	O
or	O
"	O
prefix	O
"	O
around	O
the	O
pure	O
JSON	B-General_Concept
.	O
</s>
<s>
For	O
JSONP	B-General_Concept
to	O
work	O
,	O
a	O
server	O
must	O
reply	O
with	O
a	O
response	O
that	O
includes	O
the	O
JSONP	B-General_Concept
function	O
.	O
</s>
<s>
JSONP	B-General_Concept
does	O
not	O
work	O
with	O
JSON-formatted	O
results	O
.	O
</s>
<s>
The	O
JSONP	B-General_Concept
function	O
invocation	O
that	O
gets	O
sent	O
back	O
,	O
and	O
the	O
payload	O
that	O
the	O
function	O
receives	O
,	O
must	O
be	O
agreed	O
upon	O
by	O
the	O
client	O
and	O
server	O
.	O
</s>
<s>
By	O
convention	O
,	O
the	O
server	O
providing	O
the	O
JSON	B-General_Concept
data	O
offers	O
the	O
requesting	O
website	O
to	O
name	O
the	O
JSONP	B-General_Concept
function	O
,	O
typically	O
using	O
the	O
name	O
jsonp	B-General_Concept
or	O
callback	O
as	O
the	O
named	O
query-string	O
parameter	O
,	O
in	O
its	O
request	O
to	O
the	O
server	O
:	O
<script src="http://server.example.com/Users/1234?callback=parseResponse"></script>	O
.	O
</s>
<s>
JSONP	B-General_Concept
makes	O
sense	O
only	O
when	O
used	O
with	O
a	O
script	O
element	O
.	O
</s>
<s>
For	O
each	O
new	O
JSONP	B-General_Concept
request	O
,	O
the	O
browser	O
must	O
add	O
a	O
new	O
<script>	O
element	O
,	O
or	O
reuse	O
an	O
existing	O
one	O
.	O
</s>
<s>
The	O
<script>	O
element	O
is	O
injected	O
into	O
the	O
HTML	O
DOM	O
,	O
with	O
the	O
URL	O
of	O
the	O
desired	O
JSONP	B-General_Concept
endpoint	O
set	O
as	O
the	O
"	O
src	O
"	O
attribute	O
.	O
</s>
<s>
jQuery	B-Language
and	O
other	O
frameworks	O
have	O
JSONP	B-General_Concept
helper	O
functions	O
;	O
there	O
are	O
also	O
standalone	O
options	O
.	O
</s>
<s>
An	O
example	O
of	O
using	O
jQuery	B-Language
to	O
dynamically	O
inject	O
script	O
element	O
for	O
a	O
JSONP	B-General_Concept
call	O
looks	O
like	O
this	O
:	O
</s>
<s>
In	O
that	O
way	O
,	O
the	O
use	O
of	O
JSONP	B-General_Concept
can	O
allow	O
browser	O
pages	O
to	O
work	O
around	O
the	O
same-origin	B-Protocol
policy	I-Protocol
via	O
script	O
element	O
injection	O
.	O
</s>
<s>
This	O
means	O
that	O
a	O
web	O
page	O
cannot	O
,	O
for	O
example	O
,	O
load	O
a	O
library	O
hosted	O
on	O
another	O
site	O
via	O
JSONP	B-General_Concept
and	O
then	O
make	O
XMLHttpRequest	O
requests	O
to	O
that	O
site	O
(	O
unless	O
cross-origin	B-General_Concept
resource	I-General_Concept
sharing	I-General_Concept
(	O
CORS	B-General_Concept
)	O
is	O
supported	O
)	O
,	O
although	O
one	O
could	O
use	O
such	O
a	O
library	O
to	O
make	O
XMLHttpRequests	O
to	O
one	O
's	O
own	O
site	O
.	O
</s>
<s>
If	O
an	O
attacker	O
can	O
inject	O
any	O
JavaScript	O
into	O
the	O
original	O
web	O
page	O
,	O
then	O
that	O
code	O
can	O
retrieve	O
additional	O
JavaScript	O
from	O
any	O
domain	O
,	O
bypassing	O
the	O
same-origin	B-Protocol
policy	I-Protocol
.	O
</s>
<s>
An	O
effort	O
was	O
undertaken	O
around	O
2011	O
to	O
define	O
a	O
safer	O
strict	O
subset	O
definition	O
for	O
JSONP	B-General_Concept
that	O
browsers	O
would	O
be	O
able	O
to	O
enforce	O
on	O
script	O
requests	O
with	O
a	O
specific	O
MIME	B-Protocol
type	O
such	O
as	O
"	O
application/json	O
-p	O
"	O
.	O
</s>
<s>
If	O
the	O
response	O
did	O
not	O
parse	O
as	O
strict	O
JSONP	B-General_Concept
,	O
the	O
browser	O
could	O
throw	O
an	O
error	O
or	O
just	O
ignore	O
the	O
entire	O
response	O
.	O
</s>
<s>
However	O
,	O
this	O
approach	O
was	O
abandoned	O
in	O
favor	O
of	O
CORS	B-General_Concept
,	O
and	O
the	O
correct	O
MIME	B-Protocol
type	O
for	O
JSONP	B-General_Concept
remains	O
application/javascript	O
.	O
</s>
<s>
JSONP	B-General_Concept
carried	O
the	O
same	O
problems	O
as	O
resolving	O
JSON	B-General_Concept
with	O
:	O
both	O
interpret	O
the	O
JSON	B-General_Concept
text	O
as	O
JavaScript	O
,	O
which	O
meant	O
differences	O
in	O
handling	O
U+2028	O
(	O
Line	O
Separator	O
)	O
and	O
U+2029	O
(	O
Paragraph	O
Separator	O
)	O
from	O
JSON	B-General_Concept
proper	O
.	O
</s>
<s>
This	O
made	O
some	O
JSON	B-General_Concept
strings	O
non-legal	O
in	O
JSONP	B-General_Concept
;	O
servers	O
serving	O
JSONP	B-General_Concept
had	O
to	O
escape	O
these	O
characters	O
prior	O
to	O
transmission	O
.	O
</s>
<s>
Unsanitized	O
callback	O
names	O
may	O
be	O
used	O
to	O
pass	O
malicious	O
data	O
to	O
clients	O
,	O
bypassing	O
the	O
restrictions	O
associated	O
with	O
application/json	O
content	O
type	O
,	O
as	O
demonstrated	O
in	O
reflected	O
file	O
download	O
(	O
RFD	O
)	O
attack	O
from	O
2014	O
.	O
</s>
<s>
Insecure	O
JSONP	B-General_Concept
endpoints	O
can	O
be	O
also	O
injected	O
with	O
malicious	O
data	O
.	O
</s>
<s>
Naive	O
deployments	O
of	O
JSONP	B-General_Concept
are	O
subject	O
to	O
cross-site	B-Protocol
request	I-Protocol
forgery	I-Protocol
(	O
CSRF	B-Protocol
or	O
XSRF	B-Protocol
)	O
attacks	O
.	O
</s>
<s>
Because	O
the	O
HTML	O
<script>	O
element	O
does	O
not	O
respect	O
the	O
same-origin	B-Protocol
policy	I-Protocol
in	O
web	O
browser	O
implementations	O
,	O
a	O
malicious	O
page	O
can	O
request	O
and	O
obtain	O
JSON	B-General_Concept
data	O
belonging	O
to	O
another	O
site	O
.	O
</s>
<s>
This	O
will	O
allow	O
the	O
JSON-encoded	O
data	O
to	O
be	O
evaluated	O
in	O
the	O
context	O
of	O
the	O
malicious	O
page	O
,	O
possibly	O
divulging	O
passwords	O
or	O
other	O
sensitive	O
data	O
if	O
the	O
user	O
is	O
currently	O
logged	O
into	O
the	O
other	O
site	O
.	O
</s>
<s>
Rosetta	O
Flash	O
is	O
an	O
exploitation	O
technique	O
that	O
allows	O
an	O
attacker	O
to	O
exploit	O
servers	O
with	O
a	O
vulnerable	O
JSONP	B-General_Concept
endpoint	O
by	O
causing	O
Adobe	B-Operating_System
Flash	I-Operating_System
Player	I-Operating_System
to	O
believe	O
that	O
an	O
attacker-specified	O
Flash	O
applet	O
originated	O
on	O
the	O
vulnerable	O
server	O
.	O
</s>
<s>
Flash	B-Operating_System
Player	I-Operating_System
implements	O
same-origin	B-Protocol
policy	I-Protocol
allowing	O
one	O
to	O
make	O
requests	O
(	O
with	O
cookies	O
)	O
and	O
receive	O
responses	O
from	O
the	O
hosting	O
site	O
.	O
</s>
<s>
The	O
exploit	O
uses	O
an	O
ActionScript	O
payload	O
compiled	O
to	O
an	O
SWF	O
file	O
composed	O
entirely	O
of	O
alphanumeric	O
characters	O
by	O
crafting	O
a	O
zlib	B-Language
stream	O
with	O
a	O
particular	O
header	O
and	O
DEFLATE	B-Algorithm
blocks	O
with	O
ad-hoc	O
Huffman	B-General_Concept
coding	I-General_Concept
.	O
</s>
<s>
The	O
resulting	O
alphanumeric-only	O
SWF	O
file	O
is	O
then	O
used	O
as	O
the	O
callback	O
parameter	O
of	O
a	O
JSONP	B-General_Concept
call	O
.	O
</s>
<s>
Adobe	B-Operating_System
Flash	I-Operating_System
Player	I-Operating_System
release	O
version	O
14.0.0.145	O
,	O
released	O
on	O
July	O
8	O
,	O
2014	O
,	O
introduced	O
stronger	O
validation	O
of	O
Flash	O
files	O
,	O
and	O
in	O
version	O
14.0.0.176	O
,	O
released	O
on	O
August	O
12	O
,	O
2014	O
,	O
finalized	O
the	O
fix	O
,	O
preventing	O
this	O
exploit	O
from	O
working	O
.	O
</s>
<s>
In	O
July	O
2005	O
,	O
George	O
Jempty	O
suggested	O
an	O
optional	O
variable	O
assignment	O
be	O
prepended	O
to	O
JSON	B-General_Concept
.	O
</s>
<s>
The	O
original	O
proposal	O
for	O
JSONP	B-General_Concept
,	O
where	O
the	O
padding	O
is	O
a	O
callback	O
function	O
,	O
appears	O
to	O
have	O
been	O
made	O
by	O
Bob	O
Ippolito	O
in	O
December	O
2005	O
and	O
is	O
now	O
used	O
by	O
many	O
Web	O
2.0	O
applications	O
such	O
as	O
Dojo	B-General_Concept
Toolkit	I-General_Concept
and	O
Google	B-Language
Web	I-Language
Toolkit	I-Language
.	O
</s>
