<s>
authbind	B-Protocol
is	O
an	O
open-source	B-Application
system	B-Application
utility	I-Application
written	O
by	O
Ian	O
Jackson	O
and	O
is	O
distributed	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
.	O
</s>
<s>
The	O
authbind	B-Protocol
software	B-Application
allows	O
a	O
program	B-Application
that	O
would	O
normally	O
require	O
superuser	B-Application
privileges	O
to	O
access	O
privileged	O
network	B-General_Concept
services	I-General_Concept
to	O
run	O
as	O
a	O
non-privileged	O
user	O
.	O
</s>
<s>
authbind	B-Protocol
allows	O
the	O
system	B-Application
administrator	I-Application
to	O
permit	O
specific	O
users	O
and	O
groups	O
access	O
to	O
bind	O
to	O
TCP	B-Protocol
and	I-Protocol
UDP	I-Protocol
ports	I-Protocol
below	O
1024	O
.	O
</s>
<s>
Ports	B-Protocol
0	O
-	O
1023	O
are	O
normally	O
privileged	O
and	O
reserved	O
for	O
programs	O
that	O
are	O
run	O
as	O
the	O
root	B-Application
user	I-Application
.	O
</s>
<s>
Allowing	O
regular	O
users	O
limited	O
access	O
to	O
privileged	O
ports	B-Protocol
helps	O
prevent	O
possible	O
privilege	O
escalation	O
and	O
system	O
compromise	O
if	O
the	B-Application
software	I-Application
happens	O
to	O
contain	O
software	B-Error_Name
bugs	I-Error_Name
or	O
is	O
found	O
to	O
be	O
vulnerable	O
to	O
unknown	O
exploits	O
.	O
</s>
<s>
authbind	B-Protocol
achieves	O
this	O
by	O
defining	O
the	O
LD_PRELOAD	B-Application
environment	O
variable	O
which	O
loads	O
a	O
libauthbind	O
library	O
.	O
</s>
<s>
This	O
library	O
overrides	O
the	O
bind( )	O
call	O
with	O
a	O
version	O
that	O
executes	O
a	O
setuid	O
helper	O
program	B-Application
(	O
/usr/lib/authbind/helper	O
)	O
with	O
the	O
socket	O
as	O
file	O
descriptor	O
0	O
.	O
</s>
<s>
authbind	B-Protocol
is	O
currently	O
distributed	O
with	O
the	O
Debian	O
and	O
Ubuntu	B-Operating_System
Linux	I-Operating_System
distributions	I-Operating_System
.	O
</s>
<s>
The	O
Linux	O
kernel	O
's	O
implementation	O
of	O
POSIX	O
capabilities	O
includes	O
the	O
CAP_NET_BIND_SERVICE	O
which	O
allows	O
either	O
explicitly	O
enabled	O
binaries	O
(	O
with	O
"	O
setcap	O
CAP_NET_BIND_SERVICE+ep	O
/path/to/binary	O
"	O
)	O
or	O
binaries	O
configured	O
to	O
accept	O
the	O
capability	O
from	O
the	O
invoking	O
user	O
's	O
capability	O
set	O
(	O
"	O
setcap	O
CAP_NET_BIND_SERVICE+ei	O
/path/to/binary	O
"	O
)	O
if	O
available	O
,	O
making	O
userland	O
software	B-Application
unnecessary	O
for	O
binding	O
to	O
lower	O
numeral	O
ports	B-Protocol
.	O
</s>
<s>
Linux	O
capabilities	O
,	O
however	O
were	O
not	O
introduced	O
until	O
the	O
latter	O
half	O
of	O
1999	O
,	O
more	O
than	O
a	O
year	O
after	O
authbind	B-Protocol
's	O
release	O
,	O
and	O
(	O
similar	O
to	O
setuid/setgid	O
)	O
cannot	O
be	O
set	O
on	O
scripts	O
.	O
</s>
<s>
Both	O
these	O
explain	O
why	O
the	B-Application
software	I-Application
was	O
initially	O
developed	O
.	O
</s>
