<s>
A	O
web	B-Protocol
application	I-Protocol
firewall	I-Protocol
(	O
WAF	O
)	O
is	O
a	O
specific	O
form	O
of	O
application	B-Protocol
firewall	I-Protocol
that	O
filters	O
,	O
monitors	O
,	O
and	O
blocks	O
HTTP	B-Protocol
traffic	O
to	O
and	O
from	O
a	O
web	B-Application
service	I-Application
.	O
</s>
<s>
By	O
inspecting	O
HTTP	B-Protocol
traffic	O
,	O
it	O
can	O
prevent	O
attacks	O
exploiting	O
a	O
web	B-Application
application	I-Application
's	O
known	O
vulnerabilities	O
,	O
such	O
as	O
SQL	B-Language
injection	I-Language
,	O
cross-site	O
scripting	O
(	O
XSS	O
)	O
,	O
file	B-Protocol
inclusion	I-Protocol
,	O
and	O
improper	O
system	O
configuration	O
.	O
</s>
<s>
Dedicated	O
web	B-Protocol
application	I-Protocol
firewalls	I-Protocol
entered	O
the	O
market	O
in	O
the	O
late	O
1990s	O
during	O
a	O
time	O
when	O
web	B-Application
server	I-Application
attacks	B-Application
were	O
becoming	O
more	O
prevalent	O
.	O
</s>
<s>
An	O
early	O
version	O
of	O
WAF	O
was	O
developed	O
by	O
Perfecto	O
Technologies	O
with	O
its	O
AppShield	B-Protocol
product	O
,	O
which	O
focused	O
on	O
the	O
e-commerce	O
market	O
and	O
protected	O
against	O
illegal	O
web	O
page	O
character	O
entries	O
.	O
</s>
<s>
Other	O
early	O
WAF	O
products	O
,	O
from	O
Kavado	O
and	O
Gilian	O
technologies	O
,	O
were	O
available	O
in	O
the	O
market	O
at	O
the	O
same	O
time	O
,	O
trying	O
to	O
solve	O
the	O
increasing	O
amount	O
of	O
attacks	O
on	O
web	B-Application
applications	I-Application
in	O
the	O
late	O
90s	O
.	O
</s>
<s>
In	O
2002	O
,	O
the	O
open	O
source	O
project	O
ModSecurity	B-Language
was	O
formed	O
in	O
order	O
to	O
make	O
WAF	O
technology	O
more	O
accessible	O
.	O
</s>
<s>
They	O
finalized	O
a	O
core	O
rule	O
set	O
for	O
protecting	O
web	B-Application
applications	I-Application
,	O
based	O
on	O
OASIS	O
Web	B-Application
Application	I-Application
Security	O
Technical	O
Committee	O
’s	O
(	O
WAS	O
TC	O
)	O
vulnerability	O
work	O
.	O
</s>
<s>
In	O
2003	O
,	O
they	O
expanded	O
and	O
standardized	O
rules	O
through	O
the	O
Open	O
Web	B-Application
Application	I-Application
Security	O
Project	O
’s	O
(	O
OWASP	O
)	O
Top	O
10	O
List	O
,	O
an	O
annual	O
ranking	O
for	O
web	O
security	O
vulnerabilities	O
.	O
</s>
<s>
This	O
list	O
would	O
become	O
the	O
industry	O
standard	O
for	O
web	B-Application
application	I-Application
security	O
compliance	O
.	O
</s>
<s>
A	O
web	B-Protocol
application	I-Protocol
firewall	I-Protocol
is	O
a	O
special	O
type	O
of	O
application	B-Protocol
firewall	I-Protocol
that	O
applies	O
specifically	O
to	O
web	B-Application
applications	I-Application
.	O
</s>
<s>
It	O
is	O
deployed	O
in	O
front	O
of	O
web	B-Application
applications	I-Application
and	O
analyzes	O
bi-directional	O
web-based	B-Application
(	O
HTTP	B-Protocol
)	O
traffic	O
-	O
detecting	O
and	O
blocking	O
anything	O
malicious	O
.	O
</s>
<s>
The	O
OWASP	O
provides	O
a	O
broad	O
technical	O
definition	O
for	O
a	O
WAF	O
as	O
“	O
a	O
security	O
solution	O
on	O
the	O
web	B-Application
application	I-Application
level	O
which	O
-	O
from	O
a	O
technical	O
point	O
of	O
view	O
-	O
does	O
not	O
depend	O
on	O
the	O
application	O
itself.	O
”	O
According	O
to	O
the	O
PCI	O
DSS	O
Information	O
Supplement	O
for	O
requirement	O
6.6	O
,	O
a	O
WAF	O
is	O
defined	O
as	O
“	O
a	O
security	O
policy	O
enforcement	O
point	O
positioned	O
between	O
a	O
web	B-Application
application	I-Application
and	O
the	O
client	O
endpoint	O
.	O
</s>
<s>
It	O
may	O
be	O
a	O
stand-alone	O
device	O
or	O
integrated	O
into	O
other	O
network	O
components.	O
”	O
In	O
other	O
words	O
,	O
a	O
WAF	O
can	O
be	O
a	O
virtual	O
or	O
physical	O
appliance	O
that	O
prevents	O
vulnerabilities	O
in	O
web	B-Application
applications	I-Application
from	O
being	O
exploited	O
by	O
outside	O
threats	O
.	O
</s>
<s>
A	O
web	B-Application
application	I-Application
vulnerability	O
scanner	O
,	O
also	O
known	O
as	O
a	O
web	B-Application
application	I-Application
security	O
scanner	O
,	O
is	O
defined	O
in	O
the	O
SAMATE	O
NIST	O
500-269	O
as	O
“	O
an	O
automated	O
program	O
that	O
examines	O
web	B-Application
applications	I-Application
for	O
potential	O
security	O
vulnerabilities	O
.	O
</s>
<s>
In	O
these	O
situations	O
,	O
the	O
application	O
of	O
a	O
custom	O
policy	O
for	O
a	O
unique	O
web	B-Application
application	I-Application
vulnerability	O
to	O
provide	O
a	O
temporary	O
but	O
immediate	O
fix	O
(	O
known	O
as	O
a	O
virtual	O
patch	O
)	O
may	O
be	O
necessary	O
.	O
</s>
<s>
WAFs	O
use	O
a	O
combination	O
of	O
rule-based	O
logic	O
,	O
parsing	B-Language
,	O
and	O
signatures	O
to	O
detect	O
and	O
prevent	O
attacks	O
such	O
as	O
cross-site	O
scripting	O
and	O
SQL	B-Language
injection	I-Language
.	O
</s>
<s>
The	O
OWASP	O
produces	O
a	O
list	O
of	O
the	O
top	O
ten	O
web	B-Application
application	I-Application
security	O
flaws	O
.	O
</s>
<s>
As	O
mentioned	O
earlier	O
,	O
the	O
well-known	O
open	O
source	O
WAF	O
engine	O
called	O
ModSecurity	B-Language
is	O
one	O
of	O
these	O
options	O
.	O
</s>
<s>
A	O
WAF	O
engine	O
alone	O
is	O
insufficient	O
to	O
provide	O
adequate	O
protection	O
,	O
therefore	O
OWASP	O
along	O
with	O
Trustwave	O
's	O
Spiderlabs	O
help	O
organize	O
and	O
maintain	O
a	O
Core-Rule	O
Set	O
via	O
GitHub	B-Application
to	O
use	O
with	O
the	O
ModSecurity	B-Language
WAF	O
engine	O
.	O
</s>
<s>
According	O
to	O
NSS	O
Labs	O
,	O
deployment	O
options	O
are	O
transparent	O
bridge	O
,	O
transparent	O
reverse	B-General_Concept
proxy	I-General_Concept
,	O
and	O
reverse	B-General_Concept
proxy	I-General_Concept
.	O
</s>
<s>
'	O
Transparent	O
 '	O
refers	O
to	O
the	O
fact	O
that	O
the	O
HTTP	B-Protocol
traffic	O
is	O
sent	O
straight	O
to	O
the	O
web	B-Application
application	I-Application
,	O
therefore	O
the	O
WAF	O
is	O
transparent	O
between	O
the	O
client	O
and	O
server	O
.	O
</s>
<s>
This	O
is	O
in	O
contrast	O
to	O
reverse	B-General_Concept
proxy	I-General_Concept
,	O
where	O
the	O
WAF	O
acts	O
as	O
a	O
proxy	O
and	O
the	O
client	O
’s	O
traffic	O
is	O
sent	O
directly	O
to	O
the	O
WAF	O
.	O
</s>
<s>
The	O
WAF	O
then	O
separately	O
sends	O
filtered	O
traffic	O
to	O
web	B-Application
applications	I-Application
.	O
</s>
