<s>
Dirty	B-Application
COW	I-Application
(	O
Dirty	B-Application
copy-on-write	I-Application
)	O
is	O
a	O
computer	O
security	O
vulnerability	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
that	O
affected	O
all	O
Linux-based	O
operating	O
systems	O
,	O
including	O
Android	B-Application
devices	O
,	O
that	O
used	O
older	O
versions	O
of	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
created	O
before	O
2018	O
.	O
</s>
<s>
It	O
is	O
a	O
local	O
privilege	O
escalation	O
bug	O
that	O
exploits	O
a	O
race	B-Operating_System
condition	I-Operating_System
in	O
the	O
implementation	O
of	O
the	O
copy-on-write	B-Language
mechanism	O
in	O
the	O
kernel	B-Operating_System
's	O
memory-management	O
subsystem	O
.	O
</s>
<s>
Computers	O
and	O
devices	O
that	O
still	O
use	O
the	O
older	O
kernels	B-Operating_System
remain	O
vulnerable	O
.	O
</s>
<s>
Because	O
of	O
the	O
race	B-Operating_System
condition	I-Operating_System
,	O
with	O
the	O
right	O
timing	O
,	O
a	O
local	O
attacker	O
can	O
exploit	O
the	O
copy-on-write	B-Language
mechanism	O
to	O
turn	O
a	O
read-only	O
mapping	O
of	O
a	O
file	O
into	O
a	O
writable	O
mapping	O
.	O
</s>
<s>
Although	O
it	O
is	O
a	O
local	O
privilege	O
escalation	O
,	O
remote	O
attackers	O
can	O
use	O
it	O
in	O
conjunction	O
with	O
other	O
exploits	O
that	O
allow	O
remote	O
execution	O
of	O
non-privileged	O
code	O
to	O
achieve	O
remote	O
root	B-Application
access	I-Application
on	O
a	O
computer	O
.	O
</s>
<s>
Dirty	B-Application
Cow	I-Application
was	O
one	O
of	O
the	O
first	O
security	O
issues	O
transparently	O
fixed	O
in	O
Ubuntu	B-Operating_System
by	O
the	O
Canonical	O
Live	B-Architecture
Patch	I-Architecture
service	O
.	O
</s>
<s>
It	O
has	O
been	O
demonstrated	O
that	O
the	O
vulnerability	O
can	O
be	O
utilized	O
to	O
root	B-Application
any	O
Android	B-Application
device	O
up	O
to	O
(	O
and	O
excluding	O
)	O
Android	B-Application
version	I-Application
7	I-Application
(	O
Nougat	O
)	O
.	O
</s>
<s>
The	O
vulnerability	O
has	O
existed	O
in	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
since	O
version	O
2.6.22	O
released	O
in	O
September	O
2007	O
,	O
and	O
there	O
is	O
information	O
about	O
it	O
being	O
actively	O
exploited	O
at	O
least	O
since	O
October	O
2016	O
.	O
</s>
<s>
The	O
vulnerability	O
has	O
been	O
patched	O
in	O
Linux	B-Operating_System
kernel	I-Operating_System
versions	O
4.8.3	O
,	O
4.7.9	O
,	O
4.4.26	O
and	O
newer	O
.	O
</s>
<s>
The	O
Dirty	B-Application
COW	I-Application
vulnerability	O
has	O
many	O
perceived	O
use	O
cases	O
including	O
proven	O
examples	O
,	O
such	O
as	O
obtaining	O
root	B-Application
permissions	O
in	O
Android	B-Application
devices	O
,	O
as	O
well	O
as	O
several	O
speculated	O
implementations	O
.	O
</s>
<s>
There	O
are	O
many	O
binaries	O
used	O
in	O
Linux	B-Operating_System
which	O
are	O
read-only	O
,	O
and	O
can	O
only	O
be	O
modified	O
or	O
written	O
to	O
by	O
a	O
user	O
of	O
higher	O
permissions	O
,	O
such	O
as	O
the	O
root	B-Application
.	O
</s>
<s>
When	O
privileges	O
are	O
escalated	O
,	O
whether	O
by	O
genuine	O
or	O
malicious	O
means	O
–	O
such	O
as	O
by	O
using	O
the	O
Dirty	B-Application
COW	I-Application
exploit	O
–	O
the	O
user	O
can	O
modify	O
usually	O
unmodifiable	O
binaries	O
and	O
files	O
.	O
</s>
<s>
If	O
a	O
malicious	O
individual	O
could	O
use	O
the	O
Dirty	B-Application
COW	I-Application
vulnerability	O
to	O
escalate	O
their	O
permissions	O
,	O
they	O
could	O
change	O
a	O
file	O
,	O
such	O
as	O
/bin/bash	B-Operating_System
,	O
so	O
that	O
it	O
performs	O
additional	O
,	O
unexpected	O
functions	O
,	O
such	O
as	O
a	O
keylogger	O
.	O
</s>
<s>
If	O
the	O
exploit	O
targets	O
a	O
program	O
which	O
is	O
run	O
with	O
root	B-Application
privileges	I-Application
,	O
the	O
exploit	O
will	O
have	O
those	O
same	O
privileges	O
.	O
</s>
<s>
At	O
the	O
dawn	O
of	O
its	O
discovery	O
,	O
anyone	O
using	O
a	O
machine	O
running	O
Linux	B-Operating_System
was	O
susceptible	O
to	O
the	O
exploit	O
.	O
</s>
<s>
Some	O
distributors	O
provide	O
patches	O
,	O
such	O
as	O
Canonical	O
,	O
who	O
provided	O
a	O
live	B-Architecture
patch	I-Architecture
.	O
</s>
<s>
In	O
the	O
absence	O
of	O
a	O
patch	O
,	O
there	O
are	O
a	O
few	O
mitigation	O
technologies	O
including	O
SystemTap	B-Application
,	O
and	O
very	O
little	O
security	O
from	O
SELinux	B-Application
or	O
AppArmor	O
.	O
</s>
<s>
When	O
given	O
the	O
opportunity	O
,	O
the	O
safest	O
route	O
is	O
to	O
upgrade	O
the	O
Linux	B-Operating_System
kernel	I-Operating_System
to	O
the	O
following	O
versions	O
:	O
</s>
