Cyber Talents New Year CTF — Note Checker SQLi Challenge

cyber guy

Hey Hunters !!, This cyber talents ctf was very crazy and excited specially this challenge -Note Checker- it was semi-hard but also very excited so lets turn into this write up. When i opened the server for first time it looks like very simple so normally the website told me that there are three users :- user, admin and hacker and every user prints different message so in my opinion this isn’t important as understanding the back end logic.

So you will ask how can i understand the application logic ? the answer simply understand how application work so first i check if the application have other users by trying some fuzzing but it isn’t have any other users then i check if the application can print out more than one user message and also it doesn’t print out more than one user message then i test if the application print out SQL error when i end the query by adding — { ‘ } quote -for example and it prints error and from the error i found that the DBMS was SQLite so that i read about SQLite and it’s syntax.

After that i do some parameter fuzzing to the URL and i didn’t found any other parameters in this URL so that i started to test the queries first i tried the boolean based SQLi so i tested ‘ OR 1=1; — but unfortunately the back-end system trim any spaces so i tried tow things first i try to make a concatenation using + like JavaScript but also it doesn’t work all times which mean you cant use it in a full query you can just use it once so that i remembered that i used a technique to bypass firewall in a penetration testing and this method is to use the multiple line comment instead of spaces It’s Also A Tamper In SQLMap Named space2comment so i tried this and BINGO! it works so i tried ‘/**/1=1; — and it retrieved the 0 indexed user which admin and his comment so that i knew that i cant dump the tables or the columns using the boolean based SQLi.

So i think of tow methods first is :- UNION Based SQLi Or Using {;} To End The Current Query so first i tried to end the current query by adding {;} but unfortunately the back end doesn’t allow you to do that then before i start testing UNION BASED i checked tow things First :- the maximum number of characters that you can enter in one query second the number of columns.

So first i checked the front end and i found the maximum characters is 20 after that i tried to types long queries and i found it just read the first 20 characters.So i took a rest and think of it then my friend told me that why not to test HTTP Parameter Pollution and i fired up the challenge again and start to do that and it really works.

So i tried to know how much columns the query take and here i knew that because of tow reasons, first there are three users so the query will work like that :- SELECT user,admin,hacker FROM users WHERE user=’ And Here I Type The User In The Front End’ so this is the first thing, second i tried the ORDER BY method so i typed http://3.122.109.236:3334/?q=‘/**/ORDER/**/BY/**/&q=6; — and this works and gives me that the maximum column number is 3 so that i started to craft the query.

Because i already searched about SQLite i knew that the schema database here names sqlite_master and there is a table on it named sql and it stores the text which describes the SQL queries like CREATE TABLE so i started craft the payload like that :- http://3.122.109.236:3334/?q=‘/**/UNION/**/SELECT&q=’a’,sql,’b’/**/&q=from/**/(sqlite_master)&q=limit/**/1,1 — so first here i started the query with union to perform another query then i selected the three columns that the query need and there are tow columns are arbitrary inputs -> ‘a’,’b’ and one that the table which i wanna dump it then i put the DB name in tow square brackets tow allow us to type special characters without causing query fault then i put the limit here to limit what the out put that will prints out to me and finally i put the — to comment any other queries.

Then The Database prints out what i expect which is the description of the query and it was the description of CREATE TABLE query and i found what i need to get the flag on it, i found the column :- flag and the table:- secret after that i crafted the query again and it was :- http://3.122.109.236:3334/?q=‘/**/UNION/**/SELECT&q=’a’,flag,’b’/**/&q=from/**/(secret)&q=— then the flag prints out and it was :- FLAG{parameter_pllution_bypasses_all_security}.

So this was a very exciting ctf i played ever because it need a lot of thinking to solve it but not just thinking but also creativity to perform good effort on it.

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Penetration Tester | Bug Hunter | Cyber Security Instructor | CTF Dev & Player

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Momen Ali (Cyber Guy)

Momen Ali (Cyber Guy)

Penetration Tester | Bug Hunter | Cyber Security Instructor | CTF Dev & Player

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