<s>
Squatting	B-Operating_System
attack	I-Operating_System
,	O
in	O
computer	B-General_Concept
science	I-General_Concept
,	O
is	O
a	O
kind	O
of	O
DoS	O
attack	O
where	O
a	O
program	B-Application
interferes	O
with	O
another	O
program	B-Application
through	O
the	O
use	O
of	O
shared	O
synchronization	O
objects	O
in	O
an	O
unwanted	O
or	O
unexpected	O
way	O
.	O
</s>
<s>
That	O
attack	O
is	O
known	O
in	O
the	O
Microsoft	B-Application
Windows	I-Application
operating	I-Application
system	I-Application
,	O
which	O
offers	O
named	O
objects	O
as	O
an	O
interprocess	O
synchronization	O
mechanism	O
.	O
</s>
<s>
The	O
squatting	B-Operating_System
attack	I-Operating_System
is	O
possible	O
because	O
,	O
if	O
the	O
legitimate	O
program	B-Application
does	O
not	O
enforce	O
tight	O
security	O
rules	O
for	O
the	O
resources	O
,	O
processes	O
from	O
arbitrary	O
security	O
contexts	O
may	O
gain	O
access	O
to	O
them	O
and	O
ultimately	O
take	O
control	O
of	O
the	O
system	O
.	O
</s>
<s>
Consider	O
,	O
for	O
example	O
,	O
antivirus	B-Application
software	I-Application
installed	O
on	O
a	O
Microsoft	B-Application
Windows	I-Application
machine	O
.	O
</s>
<s>
The	O
solution	O
has	O
two	O
pieces	O
:	O
a	O
service	O
,	O
which	O
monitors	O
and	O
scans	O
every	O
file	O
when	O
it	O
is	O
opened	O
,	O
and	O
a	O
manual	O
scanner	O
,	O
which	O
scans	O
the	O
file	B-Application
system	I-Application
when	O
a	O
user	O
requests	O
it	O
.	O
</s>
<s>
The	O
manual	O
scanner	O
,	O
then	O
,	O
to	O
operate	O
,	O
opens	O
the	O
named	O
event	O
,	O
sets	O
it	O
before	O
scanning	O
(	O
disabling	O
the	O
service	O
)	O
,	O
scans	O
the	O
file	B-Application
system	I-Application
and	O
resets	O
the	O
event	O
back	O
when	O
finished	O
.	O
</s>
<s>
This	O
design	O
is	O
prone	O
to	O
a	O
squatting	B-Operating_System
attack	I-Operating_System
because	O
a	O
malicious	O
program	B-Application
can	O
set	O
the	O
named	O
event	O
and	O
disable	O
the	O
service	O
completely	O
.	O
</s>
