<s>
DenyHosts	B-Application
is	O
a	O
log-based	O
intrusion-prevention	O
security	O
tool	O
for	O
SSH	B-Protocol
servers	O
written	O
in	O
Python	B-Language
.	O
</s>
<s>
It	O
is	O
intended	O
to	O
prevent	O
brute-force	O
attacks	O
on	O
SSH	B-Protocol
servers	O
by	O
monitoring	O
invalid	O
login	O
attempts	O
in	O
the	O
authentication	O
log	B-Application
and	O
blocking	O
the	O
originating	O
IP	B-Protocol
addresses	I-Protocol
.	O
</s>
<s>
DenyHosts	B-Application
is	O
developed	O
by	O
Phil	O
Schwartz	O
,	O
who	O
is	O
also	O
the	O
developer	O
of	O
Kodos	O
Python	B-Language
Regular	O
Expression	O
Debugger	O
.	O
</s>
<s>
DenyHosts	B-Application
checks	O
the	O
end	O
of	O
the	O
authentication	O
log	B-Application
for	O
recent	O
failed	O
login	O
attempts	O
.	O
</s>
<s>
It	O
records	O
information	O
about	O
their	O
originating	O
IP	B-Protocol
addresses	I-Protocol
and	O
compares	O
the	O
number	O
of	O
invalid	O
attempts	O
to	O
a	O
user-specified	O
threshold	O
.	O
</s>
<s>
If	O
there	O
have	O
been	O
too	O
many	O
invalid	O
attempts	O
it	O
assumes	O
a	O
dictionary	O
attack	O
is	O
occurring	O
and	O
prevents	O
the	O
IP	B-Protocol
address	I-Protocol
from	O
making	O
any	O
further	O
attempts	O
by	O
adding	O
it	O
to	O
/etc/hosts.deny	O
on	O
the	O
server	O
.	O
</s>
<s>
DenyHosts	B-Application
2.0	O
and	O
above	O
support	O
centralized	O
synchronization	O
,	O
so	O
that	O
repeat	O
offenders	O
are	O
blocked	O
from	O
many	O
computers	O
.	O
</s>
<s>
DenyHosts	B-Application
is	O
restricted	O
to	O
connections	O
using	O
IPv4	B-Protocol
.	O
</s>
<s>
It	O
does	O
not	O
work	O
with	O
IPv6	B-Protocol
.	O
</s>
<s>
DenyHosts	B-Application
may	O
be	O
run	O
manually	O
,	O
as	O
a	O
daemon	B-Operating_System
,	O
or	O
as	O
a	O
cron	B-General_Concept
job	I-General_Concept
.	O
</s>
<s>
In	O
July	O
2007	O
,	O
The	O
Register	O
reported	O
that	O
from	O
May	O
until	O
July	O
that	O
year	O
,	O
"	O
compromised	O
computers	O
"	O
at	O
Oracle	O
UK	O
were	O
listed	O
among	O
the	O
ten	O
worst	O
offenders	O
for	O
launching	O
brute	O
force	O
SSH	B-Protocol
attacks	O
on	O
the	O
Internet	O
,	O
according	O
to	O
public	O
DenyHosts	B-Application
listings	O
.	O
</s>
<s>
Daniel	O
B	O
.	O
Cid	O
wrote	O
a	O
paper	O
showing	O
that	O
DenyHosts	B-Application
,	O
as	O
well	O
the	O
similar	O
programs	O
Fail2ban	B-Protocol
and	O
BlockHosts	O
,	O
were	O
vulnerable	O
to	O
remote	O
log	B-Application
injection	O
,	O
an	O
attack	O
technique	O
similar	O
to	O
SQL	B-Language
injection	I-Language
,	O
in	O
which	O
a	O
specially	O
crafted	O
user	O
name	O
is	O
used	O
to	O
trigger	O
a	O
block	O
against	O
a	O
site	O
chosen	O
by	O
the	O
attacker	O
.	O
</s>
<s>
Since	O
there	O
had	O
been	O
no	O
further	O
development	O
by	O
the	O
original	O
author	O
Phil	O
Schwartz	O
after	O
the	O
release	O
of	O
version	O
2.6	O
(	O
December	O
2006	O
)	O
and	O
claimed	O
version	O
2.7	O
(	O
November	O
2008	O
)	O
for	O
which	O
no	O
actual	O
downloadable	O
package	O
is	O
available	O
,	O
development	O
was	O
first	O
continued	O
in	O
February	O
2012	O
by	O
Matt	O
Ruffalo	O
in	O
a	O
GitHub	B-Application
repository	O
.	O
</s>
<s>
An	O
independent	O
and	O
separate	O
fork	B-Application
was	O
started	O
at	O
the	O
almost-identically	O
named	O
DenyHost	O
SourceForge	O
project	O
site	O
with	O
the	O
release	O
of	O
a	O
different	O
version	O
2.7	O
in	O
May	O
2014	O
.	O
</s>
<s>
After	O
version	O
2.9	O
,	O
the	O
new	O
SourceForge	O
project	O
has	O
merged	O
with	O
the	O
earlier	O
GitHub	B-Application
repository	O
,	O
and	O
newer	O
versions	O
are	O
available	O
via	O
both	O
means	O
.	O
</s>
<s>
The	O
software	O
that	O
runs	O
the	O
centralized	O
synchronization	O
server	O
which	O
DenyHosts	B-Application
versions	O
2.0	O
and	O
above	O
can	O
use	O
,	O
has	O
never	O
been	O
released	O
.	O
</s>
