<s>
Session	B-Protocol
poisoning	I-Protocol
(	O
also	O
referred	O
to	O
as	O
"	O
session	B-Protocol
data	I-Protocol
pollution	I-Protocol
"	O
and	O
"	O
session	B-Protocol
modification	I-Protocol
"	O
)	O
is	O
a	O
method	O
to	O
exploit	O
insufficient	O
input	O
validation	O
within	O
a	O
server	O
application	O
.	O
</s>
<s>
Typically	O
a	O
server	O
application	O
that	O
is	O
vulnerable	O
to	O
this	O
type	O
of	O
exploit	O
will	O
copy	O
user	O
input	O
into	O
session	B-Protocol
variables	O
.	O
</s>
<s>
The	O
underlying	O
vulnerability	O
is	O
a	O
state	O
management	O
problem	O
:	O
shared	O
state	O
,	O
race	B-Operating_System
condition	I-Operating_System
,	O
ambiguity	O
in	O
use	O
or	O
plain	O
unprotected	O
modifications	O
of	O
state	O
values	O
.	O
</s>
<s>
Session	B-Protocol
poisoning	I-Protocol
has	O
been	O
demonstrated	O
in	O
server	O
environments	O
where	O
different	O
,	O
non-malicious	O
applications	O
(	O
scripts	O
)	O
share	O
the	O
same	O
session	B-Protocol
states	O
but	O
where	O
usage	O
differ	O
,	O
causing	O
ambiguity	O
and	O
race	B-Operating_System
conditions	I-Operating_System
.	O
</s>
<s>
Session	B-Protocol
poisoning	I-Protocol
has	O
been	O
demonstrated	O
in	O
scenarios	O
where	O
attacker	O
is	O
able	O
to	O
introduce	O
malicious	O
scripts	O
into	O
the	O
server	O
environment	O
,	O
which	O
is	O
possible	O
if	O
attacker	O
and	O
victim	O
share	O
a	O
web	O
host	O
.	O
</s>
<s>
Session	B-Protocol
poisoning	I-Protocol
was	O
first	O
discussed	O
as	O
a	O
(	O
potentially	O
new	O
)	O
vulnerability	O
class	O
in	O
the	O
Full	B-General_Concept
disclosure	I-General_Concept
mailing	O
list	O
.	O
</s>
<s>
Alla	O
Bezroutchko	O
inquired	O
if	O
"	O
Session	B-Protocol
data	I-Protocol
pollution	I-Protocol
vulnerabilities	O
in	O
web	O
applications	O
"	O
was	O
a	O
new	O
problem	O
in	O
January	O
2006	O
.	O
</s>
<s>
Session	B-Protocol
pollution	O
has	O
also	O
been	O
covered	O
in	O
some	O
articles	O
,	O
such	O
as	O
PHP	B-Application
Session	B-Protocol
Security	O
,	O
Przemek	O
Sobstel	O
,	O
2007	O
.	O
</s>
<s>
In	O
the	O
login	O
scripts	O
,	O
the	O
session	B-Protocol
variable	O
stores	O
"	O
This	O
user	O
is	O
logged	O
on	O
"	O
.	O
</s>
<s>
In	O
the	O
password	O
reset	O
scripts	O
,	O
the	O
session	B-Protocol
variable	O
stores	O
"	O
this	O
user	O
wants	O
his	O
password	O
reset	O
"	O
.	O
</s>
<s>
A	O
race	B-Operating_System
condition	I-Operating_System
was	O
demonstrated	O
,	O
in	O
which	O
the	O
reset	O
scripts	O
could	O
be	O
exploited	O
to	O
change	O
the	O
logged	O
on	O
user	O
arbitrarily	O
.	O
</s>
<s>
Alla	O
Bezroutchko	O
discusses	O
examples	O
observed	O
in	O
development	O
forums	O
,	O
which	O
allows	O
writing	O
to	O
arbitrary	O
session	B-Protocol
variables	O
.	O
</s>
<s>
php.ini	O
:	O
register_globals	O
=	O
on	O
is	O
known	O
to	O
enable	O
security	O
vulnerabilities	O
in	O
several	O
applications	O
.	O
</s>
<s>
PHP	B-Application
server	O
administrators	O
are	O
recommended	O
to	O
disable	O
this	O
feature	O
.	O
</s>
<s>
Note	O
:	O
Real-world	O
examples	O
of	O
session	B-Protocol
poisoning	I-Protocol
in	O
enabled	O
by	O
register_globals	O
=	O
on	O
was	O
publicly	O
demonstrated	O
in	O
back	O
in	O
July	O
2001	O
article	O
Serious	O
security	O
hole	O
in	O
Mambo	O
Site	O
Server	O
version	O
3.0.X	O
.	O
</s>
<s>
php.ini	O
is	O
misconfigured	O
(	O
register_globals	O
=	O
on	O
)	O
,	O
which	O
allows	O
$var	O
default	O
value	O
to	O
be	O
controlled	O
by	O
GPC	O
(	O
GET	O
,	O
POST	O
,	O
or	O
COOKIE	O
)	O
input	O
.	O
</s>
<s>
'	O
unknown	O
 '	O
of	O
uw-team.org	O
discusses	O
a	O
scenario	O
where	O
attacker	O
and	O
victim	O
shares	O
the	O
same	O
PHP	B-Application
server	O
.	O
</s>
<s>
Attacker	O
then	O
uploads	O
a	O
PHP	B-Application
script	I-Application
to	O
his	O
account	O
,	O
and	O
has	O
it	O
display	O
context	O
of	O
$_SESSION	O
(	O
set	O
by	O
victim	O
script	O
)	O
.	O
</s>
<s>
This	O
attack	O
only	O
requires	O
that	O
victim	O
and	O
attacker	O
share	O
the	O
same	O
PHP	B-Application
server	O
.	O
</s>
<s>
The	O
attack	O
is	O
not	O
dependent	O
on	O
victim	O
and	O
attacker	O
having	O
the	O
same	O
virtual	O
hostname	O
,	O
as	O
it	O
is	O
trivial	O
for	O
attacker	O
to	O
move	O
the	O
session	B-Protocol
identifier	O
cookie	O
from	O
one	O
cookie	O
domain	O
to	O
another	O
.	O
</s>
