<s>
DNS	B-Protocol
hijacking	I-Protocol
,	O
DNS	B-Protocol
poisoning	O
,	O
or	O
DNS	B-Protocol
redirection	I-Protocol
is	O
the	O
practice	O
of	O
subverting	O
the	O
resolution	O
of	O
Domain	B-Protocol
Name	I-Protocol
System	I-Protocol
(	O
DNS	B-Protocol
)	O
queries	O
.	O
</s>
<s>
This	O
can	O
be	O
achieved	O
by	O
malware	O
that	O
overrides	O
a	O
computer	O
's	O
TCP/IP	B-Protocol
configuration	O
to	O
point	O
at	O
a	O
rogue	B-Protocol
DNS	I-Protocol
server	I-Protocol
under	O
the	O
control	O
of	O
an	O
attacker	O
,	O
or	O
through	O
modifying	O
the	O
behaviour	O
of	O
a	O
trusted	O
DNS	B-Protocol
server	I-Protocol
so	O
that	O
it	O
does	O
not	O
comply	O
with	O
internet	O
standards	O
.	O
</s>
<s>
These	O
modifications	O
may	O
be	O
made	O
for	O
malicious	O
purposes	O
such	O
as	O
phishing	O
,	O
for	O
self-serving	O
purposes	O
by	O
Internet	O
service	O
providers	O
(	O
ISPs	O
)	O
,	O
by	O
the	B-Application
Great	I-Application
Firewall	I-Application
of	I-Application
China	I-Application
and	O
public/router	O
-based	O
online	O
DNS	B-Protocol
server	I-Protocol
providers	I-Protocol
to	O
direct	O
users	O
 '	O
web	O
traffic	O
to	O
the	O
ISP	O
's	O
own	O
web	B-Application
servers	I-Application
where	O
advertisements	O
can	O
be	O
served	O
,	O
statistics	O
collected	O
,	O
or	O
other	O
purposes	O
of	O
the	O
ISP	O
;	O
and	O
by	O
DNS	B-Protocol
service	O
providers	O
to	O
block	O
access	O
to	O
selected	O
domains	O
as	O
a	O
form	O
of	O
censorship	O
.	O
</s>
<s>
One	O
of	O
the	O
functions	O
of	O
a	O
DNS	B-Protocol
server	I-Protocol
is	O
to	O
translate	O
a	O
domain	O
name	O
into	O
an	O
IP	B-Protocol
address	I-Protocol
that	O
applications	B-Application
need	O
to	O
connect	O
to	O
an	O
Internet	O
resource	O
such	O
as	O
a	O
website	O
.	O
</s>
<s>
DNS	B-Protocol
servers	I-Protocol
are	O
implicitly	O
trusted	O
by	O
internet-facing	O
computers	O
and	O
users	O
to	O
correctly	O
resolve	O
names	O
to	O
the	O
actual	O
addresses	O
that	O
are	O
registered	O
by	O
the	O
owners	O
of	O
an	O
internet	O
domain	O
.	O
</s>
<s>
A	O
rogue	B-Protocol
DNS	I-Protocol
server	I-Protocol
translates	O
domain	O
names	O
of	O
desirable	O
websites	O
(	O
search	O
engines	O
,	O
banks	O
,	O
brokers	O
,	O
etc	O
.	O
)	O
</s>
<s>
into	O
IP	B-Protocol
addresses	I-Protocol
of	O
sites	O
with	O
unintended	O
content	O
,	O
even	O
malicious	O
websites	O
.	O
</s>
<s>
Most	O
users	O
depend	O
on	O
DNS	B-Protocol
servers	I-Protocol
automatically	O
assigned	O
by	O
their	O
ISPs	O
.	O
</s>
<s>
A	O
router	O
's	O
assigned	O
DNS	B-Protocol
servers	I-Protocol
can	O
also	O
be	O
altered	O
through	O
the	O
remote	O
exploitation	O
of	O
a	O
vulnerability	O
within	O
the	O
router	O
's	O
firmware	O
.	O
</s>
<s>
A	O
number	O
of	O
consumer	O
ISPs	O
such	O
as	O
AT&T	O
,	O
Cablevision	O
's	O
Optimum	O
Online	O
,	O
CenturyLink	B-Application
,	O
Cox	O
Communications	O
,	O
RCN	O
,	O
Rogers	O
,	O
Charter	O
Communications	O
(	O
Spectrum	O
)	O
,	O
Plusnet	O
,	O
Verizon	B-Application
,	O
Sprint	O
,	O
T-Mobile	O
US	O
,	O
Virgin	O
Media	O
,	O
Frontier	O
Communications	O
,	O
Bell	O
Sympatico	O
,	O
Deutsche	O
Telekom	O
AG	O
,	O
Optus	O
,	O
Mediacom	O
,	O
ONO	O
,	O
TalkTalk	O
,	O
Bigpond	O
(	O
Telstra	O
)	O
,	O
TTNET	O
,	O
Türksat	O
,	O
and	O
all	O
Indonesian	O
customer	O
ISPs	O
use	O
or	O
used	O
DNS	B-Protocol
hijacking	I-Protocol
for	O
their	O
own	O
purposes	O
,	O
such	O
as	O
displaying	O
advertisements	O
or	O
collecting	O
statistics	O
.	O
</s>
<s>
Dutch	O
ISPs	O
XS4ALL	O
and	O
Ziggo	O
use	O
DNS	B-Protocol
hijacking	I-Protocol
by	O
court	O
order	O
:	O
they	O
were	O
ordered	O
to	O
block	O
access	O
to	O
The	B-Application
Pirate	I-Application
Bay	I-Application
and	O
display	O
a	O
warning	O
page	O
while	O
all	O
customer	O
ISP	O
in	O
Indonesia	O
do	O
DNS	B-Protocol
hijacking	I-Protocol
to	O
comply	O
with	O
the	O
National	O
DNS	B-Protocol
law	O
which	O
requires	O
every	O
customer	O
Indonesian	O
ISP	O
to	O
hijack	O
port	O
53	O
and	O
redirect	O
it	O
to	O
their	O
own	O
server	O
to	O
block	O
website	O
that	O
are	O
listed	O
in	O
by	O
Kominfo	O
under	O
Internet	O
Sehat	O
campaign	O
.	O
</s>
<s>
These	O
practices	O
violate	O
the	O
RFC	O
standard	O
for	O
DNS	B-Protocol
(	O
NXDOMAIN	O
)	O
responses	O
,	O
and	O
can	O
potentially	O
open	O
users	O
to	O
cross-site	O
scripting	O
attacks	O
.	O
</s>
<s>
The	O
concern	O
with	O
DNS	B-Protocol
hijacking	I-Protocol
involves	O
this	O
hijacking	O
of	O
the	O
NXDOMAIN	O
response	O
.	O
</s>
<s>
Internet	O
and	O
intranet	B-General_Concept
applications	B-Application
rely	O
on	O
the	O
NXDOMAIN	O
response	O
to	O
describe	O
the	O
condition	O
where	O
the	O
DNS	B-Protocol
has	O
no	O
entry	O
for	O
the	O
specified	O
host	O
.	O
</s>
<s>
However	O
,	O
if	O
the	O
domain	O
name	O
is	O
queried	O
on	O
one	O
of	O
these	O
non-compliant	O
ISPs	O
,	O
one	O
would	O
always	O
receive	O
a	O
fake	O
IP	B-Protocol
address	I-Protocol
belonging	O
to	O
the	O
ISP	O
.	O
</s>
<s>
In	O
a	O
web	B-Application
browser	I-Application
,	O
this	O
behavior	O
can	O
be	O
annoying	O
or	O
offensive	O
as	O
connections	O
to	O
this	O
IP	B-Protocol
address	I-Protocol
display	O
the	O
ISP	O
redirect	O
page	O
of	O
the	O
provider	O
,	O
sometimes	O
with	O
advertising	O
,	O
instead	O
of	O
a	O
proper	O
error	O
message	O
.	O
</s>
<s>
However	O
,	O
other	O
applications	B-Application
that	O
rely	O
on	O
the	O
NXDOMAIN	O
error	O
will	O
instead	O
attempt	O
to	O
initiate	O
connections	O
to	O
this	O
spoofed	O
IP	B-Protocol
address	I-Protocol
,	O
potentially	O
exposing	O
sensitive	O
information	O
.	O
</s>
<s>
Examples	O
of	O
functionality	O
that	O
breaks	O
when	O
an	O
ISP	O
hijacks	O
DNS	B-Protocol
:	O
</s>
<s>
Roaming	O
laptops	O
that	O
are	O
members	O
of	O
a	O
Windows	B-General_Concept
Server	I-General_Concept
domain	I-General_Concept
will	O
falsely	O
be	O
led	O
to	O
believe	O
that	O
they	O
are	O
back	O
on	O
a	O
corporate	O
network	O
because	O
resources	O
such	O
as	O
domain	B-Protocol
controllers	I-Protocol
,	O
email	B-Protocol
servers	I-Protocol
and	O
other	O
infrastructure	O
will	O
appear	O
to	O
be	O
available	O
.	O
</s>
<s>
Applications	B-Application
will	O
therefore	O
attempt	O
to	O
initiate	O
connections	O
to	O
these	O
corporate	O
servers	O
,	O
but	O
fail	O
,	O
resulting	O
in	O
degraded	O
performance	O
,	O
unnecessary	O
traffic	O
on	O
the	O
Internet	O
connection	O
and	O
timeouts	O
.	O
</s>
<s>
Many	O
small	O
office	O
and	O
home	O
networks	O
do	O
not	O
have	O
their	O
own	O
DNS	B-Protocol
server	I-Protocol
,	O
relying	O
instead	O
on	O
broadcast	B-Operating_System
name	O
resolution	O
.	O
</s>
<s>
Many	O
versions	O
of	O
Microsoft	O
Windows	O
default	O
to	O
prioritizing	O
DNS	B-Protocol
name	I-Protocol
resolution	O
above	O
NetBIOS	O
name	O
resolution	O
broadcasts	B-Operating_System
;	O
therefore	O
,	O
when	O
an	O
ISP	O
DNS	B-Protocol
server	I-Protocol
returns	O
a	O
(	O
technically	O
valid	O
)	O
IP	B-Protocol
address	I-Protocol
for	O
the	O
name	O
of	O
the	O
desired	O
computer	O
on	O
the	O
LAN	O
,	O
the	O
connecting	O
computer	O
uses	O
this	O
incorrect	O
IP	B-Protocol
address	I-Protocol
and	O
inevitably	O
fails	O
to	O
connect	O
to	O
the	O
desired	O
computer	O
on	O
the	O
LAN	O
.	O
</s>
<s>
Workarounds	O
include	O
using	O
the	O
correct	O
IP	B-Protocol
address	I-Protocol
instead	O
of	O
the	O
computer	O
name	O
,	O
or	O
changing	O
the	O
DhcpNodeType	O
registry	O
value	O
to	O
change	O
name	O
resolution	O
service	O
ordering	O
.	O
</s>
<s>
Browsers	B-Application
such	O
as	O
Firefox	B-Application
no	O
longer	O
have	O
their	O
'	O
Browse	O
By	O
Name	O
 '	O
functionality	O
(	O
where	O
keywords	O
typed	O
in	O
the	O
address	O
bar	O
take	O
users	O
to	O
the	O
closest	O
matching	O
site	O
)	O
.	O
</s>
<s>
The	O
local	O
DNS	B-Protocol
client	O
built	O
into	O
modern	O
operating	O
systems	O
will	O
cache	O
results	O
of	O
DNS	B-Protocol
searches	O
for	O
performance	O
reasons	O
.	O
</s>
<s>
If	O
a	O
client	O
switches	O
between	O
a	O
home	O
network	O
and	O
a	O
VPN	B-Application
,	O
false	O
entries	O
may	O
remain	O
cached	O
,	O
thereby	O
creating	O
a	O
service	O
outage	O
on	O
the	O
VPN	B-Application
connection	O
.	O
</s>
<s>
DNSBL	O
anti-spam	O
solutions	O
rely	O
on	O
DNS	B-Protocol
;	O
false	O
DNS	B-Protocol
results	O
therefore	O
interfere	O
with	O
their	O
operation	O
.	O
</s>
<s>
Confidential	O
user	O
data	O
might	O
be	O
leaked	O
by	O
applications	B-Application
that	O
are	O
tricked	O
by	O
the	O
ISP	O
into	O
believing	O
that	O
the	O
servers	O
they	O
wish	O
to	O
connect	O
to	O
are	O
available	O
.	O
</s>
<s>
User	O
choice	O
over	O
which	O
search	O
engine	O
to	O
consult	O
in	O
the	O
event	O
of	O
a	O
URL	O
being	O
mistyped	O
in	O
a	O
browser	B-Application
is	O
removed	O
as	O
the	O
ISP	O
determines	O
what	O
search	O
results	O
are	O
displayed	O
to	O
the	O
user	O
.	O
</s>
<s>
Computers	O
configured	O
to	O
use	O
a	O
split	B-Application
tunnel	I-Application
with	O
a	O
VPN	B-Application
connection	O
will	O
stop	O
working	O
because	O
intranet	B-General_Concept
names	O
that	O
should	O
not	O
be	O
resolved	O
outside	O
the	O
tunnel	O
over	O
the	O
public	O
Internet	O
will	O
start	O
resolving	O
to	O
fictitious	O
addresses	O
,	O
instead	O
of	O
resolving	O
correctly	O
over	O
the	O
VPN	B-Application
tunnel	O
on	O
a	O
private	O
DNS	B-Protocol
server	I-Protocol
when	O
an	O
NXDOMAIN	O
response	O
is	O
received	O
from	O
the	O
Internet	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
mail	O
client	O
attempting	O
to	O
resolve	O
the	O
DNS	B-Protocol
A	O
record	O
for	O
an	O
internal	O
mail	B-Protocol
server	I-Protocol
may	O
receive	O
a	O
false	O
DNS	B-Protocol
response	O
that	O
directed	O
it	O
to	O
a	O
paid-results	O
web	B-Application
server	I-Application
,	O
with	O
messages	O
queued	O
for	O
delivery	O
for	O
days	O
while	O
retransmission	O
was	O
attempted	O
in	O
vain	O
.	O
</s>
<s>
It	O
breaks	O
Web	B-Protocol
Proxy	I-Protocol
Autodiscovery	I-Protocol
Protocol	I-Protocol
(	O
WPAD	B-Protocol
)	O
by	O
leading	O
web	B-Application
browsers	I-Application
to	O
believe	O
incorrectly	O
that	O
the	O
ISP	O
has	O
a	O
proxy	B-Application
server	I-Application
configured	O
.	O
</s>
<s>
Correctly	O
implemented	O
,	O
such	O
a	O
setting	O
reverts	O
DNS	B-Protocol
to	O
standard	O
behavior	O
.	O
</s>
<s>
Other	O
ISPs	O
,	O
however	O
,	O
instead	O
use	O
a	O
web	B-Application
browser	I-Application
cookie	I-Application
to	O
store	O
the	O
preference	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
underlying	O
behavior	O
is	O
not	O
resolved	O
:	O
DNS	B-Protocol
queries	I-Protocol
continue	O
to	O
be	O
redirected	O
,	O
while	O
the	O
ISP	O
redirect	O
page	O
is	O
replaced	O
with	O
a	O
counterfeit	O
DNS	B-Protocol
error	I-Protocol
page	O
.	O
</s>
<s>
Applications	B-Application
other	O
than	O
web	B-Application
browsers	I-Application
cannot	O
be	O
opted	O
out	O
of	O
the	O
scheme	O
using	O
cookies	B-Application
as	O
the	O
opt-out	O
targets	O
only	O
the	O
HTTP	B-Protocol
protocol	I-Protocol
,	O
when	O
the	O
scheme	O
is	O
actually	O
implemented	O
in	O
the	O
protocol-neutral	O
DNS	B-Protocol
.	O
</s>
<s>
In	O
the	O
UK	O
,	O
the	O
Information	O
Commissioner	O
's	O
Office	O
has	O
acknowledged	O
that	O
the	O
practice	O
of	O
involuntary	O
DNS	B-Protocol
hijacking	I-Protocol
contravenes	O
PECR	O
,	O
and	O
EC	O
Directive	O
95/46	O
on	O
Data	O
Protection	O
which	O
require	O
explicit	O
consent	O
for	O
processing	O
of	O
communication	O
traffic	O
.	O
</s>
<s>
In	O
Germany	O
,	O
in	O
2019	O
it	O
was	O
revealed	O
that	O
the	O
Deutsche	O
Telekom	O
AG	O
not	O
only	O
manipulated	O
their	O
DNS	B-Protocol
servers	I-Protocol
,	O
but	O
also	O
transmitted	O
network	O
traffic	O
(	O
such	O
as	O
non-secure	O
cookies	B-Application
when	O
users	O
did	O
not	O
use	O
HTTPS	B-Protocol
)	O
to	O
a	O
third	O
party	O
company	O
because	O
the	O
web	O
portal	O
T-Online	O
,	O
at	O
which	O
users	O
were	O
redirected	O
due	O
to	O
the	O
DNS	B-Protocol
manipulation	O
,	O
was	O
not	O
(	O
any	O
more	O
)	O
owned	O
by	O
the	O
Deutsche	O
Telekom	O
.	O
</s>
<s>
After	O
a	O
user	O
filed	O
a	O
criminal	O
complaint	O
,	O
the	O
Deutsche	O
Telekom	O
stopped	O
further	O
DNS	B-Protocol
manipulations	O
.	O
</s>
<s>
ICANN	B-Application
,	O
the	O
international	O
body	O
responsible	O
for	O
administering	O
top-level	O
domain	O
names	O
,	O
has	O
published	O
a	O
memorandum	O
highlighting	O
its	O
concerns	O
,	O
and	O
affirming	O
:	O
</s>
<s>
End	O
users	O
,	O
dissatisfied	O
with	O
poor	O
"	O
opt-out	O
"	O
options	O
like	O
cookies	B-Application
,	O
have	O
responded	O
to	O
the	O
controversy	O
by	O
finding	O
ways	O
to	O
avoid	O
spoofed	O
NXDOMAIN	O
responses	O
.	O
</s>
<s>
DNS	B-Protocol
software	O
such	O
as	O
BIND	B-Protocol
and	O
Dnsmasq	B-Protocol
offer	O
options	O
to	O
filter	O
results	O
,	O
and	O
can	O
be	O
run	O
from	O
a	O
gateway	O
or	O
router	O
to	O
protect	O
an	O
entire	O
network	O
.	O
</s>
<s>
Google	O
,	O
among	O
others	O
,	O
run	O
open	B-Protocol
DNS	I-Protocol
servers	O
that	O
currently	O
do	O
not	O
return	O
spoofed	O
results	O
.	O
</s>
<s>
So	O
a	O
user	O
could	O
use	O
Google	B-Protocol
Public	I-Protocol
DNS	I-Protocol
instead	O
of	O
their	O
ISP	O
's	O
DNS	B-Protocol
servers	I-Protocol
if	O
they	O
are	O
willing	O
to	O
accept	O
that	O
they	O
use	O
the	O
service	O
under	O
Google	O
's	O
privacy	O
policy	O
and	O
potentially	O
be	O
exposed	O
to	O
another	O
method	O
by	O
which	O
Google	O
can	O
track	O
the	O
user	O
.	O
</s>
<s>
One	O
limitation	O
of	O
this	O
approach	O
is	O
that	O
some	O
providers	O
block	O
or	O
rewrite	O
outside	O
DNS	B-Protocol
requests	O
.	O
</s>
<s>
OpenDNS	B-Protocol
,	O
owned	O
by	O
Cisco	O
,	O
is	O
a	O
similar	O
popular	O
service	O
which	O
does	O
not	O
alter	O
NXDOMAIN	O
responses	O
.	O
</s>
<s>
Google	O
in	O
April	O
2016	O
launched	O
DNS-over-HTTPS	O
service	O
.	O
</s>
<s>
This	O
scheme	O
can	O
overcome	O
the	O
limitations	O
of	O
the	O
legacy	O
DNS	B-Protocol
protocol	I-Protocol
.	O
</s>
<s>
It	O
performs	O
remote	O
DNSSEC	O
check	O
and	O
transfers	O
the	O
results	O
in	O
a	O
secure	O
HTTPS	B-Protocol
tunnel	O
.	O
</s>
<s>
There	O
are	O
also	O
application-level	O
work-arounds	O
,	O
such	O
as	O
the	O
NoRedirect	O
Firefox	B-Operating_System
extension	I-Operating_System
,	O
that	O
mitigate	O
some	O
of	O
the	O
behavior	O
.	O
</s>
<s>
An	O
approach	O
like	O
that	O
only	O
fixes	O
one	O
application	O
(	O
in	O
this	O
example	O
,	O
Firefox	B-Application
)	O
and	O
will	O
not	O
address	O
any	O
other	O
issues	O
caused	O
.	O
</s>
<s>
Website	O
owners	O
may	O
be	O
able	O
to	O
fool	O
some	O
hijackers	O
by	O
using	O
certain	O
DNS	B-Protocol
settings	O
.	O
</s>
<s>
The	O
limitation	O
of	O
that	O
approach	O
is	O
that	O
it	O
only	O
prevents	O
hijacking	O
on	O
those	O
particular	O
domains	O
,	O
but	O
it	O
may	O
address	O
some	O
VPN	B-Application
security	O
issues	O
caused	O
by	O
DNS	B-Protocol
hijacking	I-Protocol
.	O
</s>
