MySQL Injection - Use SELECT query to UPDATE/DELETE - mysql

I've got one easy question: say there is a site with a query like:
SELECT id, name, message FROM messages WHERE id = $_GET['q'].
Is there any way to get something updated/deleted in the database (MySQL)? Until now I've never seen an injection that was able to delete/update using a SELECT query, so, is it even possible?

Before directly answering the question, it's worth noting that even if all an attacker can do is read data that he shouldn't be able to, that's usually still really bad. Consider that by using JOINs and SELECTing from system tables (like mysql.innodb_table_stats), an attacker who starts with a SELECT injection and no other knowledge of your database can map your schema and then exfiltrate the entirety of the data that you have in MySQL. For the vast majority of databases and applications, that already represents a catastrophic security hole.
But to answer the question directly: there are a few ways that I know of by which injection into a MySQL SELECT can be used to modify data. Fortunately, they all require reasonably unusual circumstances to be possible. All example injections below are given relative to the example injectable query from the question:
SELECT id, name, message FROM messages WHERE id = $_GET['q']
1. "Stacked" or "batched" queries.
The classic injection technique of just putting an entire other statement after the one being injected into. As suggested in another answer here, you could set $_GET['q'] to 1; DELETE FROM users; -- so that the query forms two statements which get executed consecutively, the second of which deletes everything in the users table.
In mitigation
Most MySQL connectors - notably including PHP's (deprecated) mysql_* and (non-deprecated) mysqli_* functions - don't support stacked or batched queries at all, so this kind of attack just plain doesn't work. However, some do - notably including PHP's PDO connector (although the support can be disabled to increase security).
2. Exploiting user-defined functions
Functions can be called from a SELECT, and can alter data. If a data-altering function has been created in the database, you could make the SELECT call it, for instance by passing 0 OR SOME_FUNCTION_NAME() as the value of $_GET['q'].
In mitigation
Most databases don't contain any user-defined functions - let alone data-altering ones - and so offer no opportunity at all to perform this sort of exploit.
3. Writing to files
As described in Muhaimin Dzulfakar's (somewhat presumptuously named) paper Advanced MySQL Exploitation, you can use INTO OUTFILE or INTO DUMPFILE clauses on a MySQL select to dump the result into a file. Since, by using a UNION, any arbitrary result can be SELECTed, this allows writing new files with arbitrary content at any location that the user running mysqld can access. Conceivably this can be exploited not merely to modify data in the MySQL database, but to get shell access to the server on which it is running - for instance, by writing a PHP script to the webroot and then making a request to it, if the MySQL server is co-hosted with a PHP server.
In mitigation
Lots of factors reduce the practical exploitability of this otherwise impressive-sounding attack:
MySQL will never let you use INTO OUTFILE or INTO DUMPFILE to overwrite an existing file, nor write to a folder that doesn't exist. This prevents attacks like creating a .ssh folder with a private key in the mysql user's home directory and then SSHing in, or overwriting the mysqld binary itself with a malicious version and waiting for a server restart.
Any halfway decent installation package will set up a special user (typically named mysql) to run mysqld, and give that user only very limited permissions. As such, it shouldn't be able to write to most locations on the file system - and certainly shouldn't ordinarily be able to do things like write to a web application's webroot.
Modern installations of MySQL come with --secure-file-priv set by default, preventing MySQL from writing to anywhere other than a designated data import/export directory and thereby rendering this attack almost completely impotent... unless the owner of the server has deliberately disabled it. Fortunately, nobody would ever just completely disable a security feature like that since that would obviously be - oh wait never mind.
4. Calling the sys_exec() function from lib_mysqludf_sys to run arbitrary shell commands
There's a MySQL extension called lib_mysqludf_sys that - judging from its stars on GitHub and a quick Stack Overflow search - has at least a few hundred users. It adds a function called sys_exec that runs shell commands. As noted in #2, functions can be called from within a SELECT; the implications are hopefully obvious. To quote from the source, this function "can be a security hazard".
In mitigation
Most systems don't have this extension installed.

If you say you use mysql_query that doesn't support multiple queries, you cannot directly add DELETE/UPDATE/INSERT, but it's possible to modify data under some circumstances. For example, let's say you have the following function
DELIMITER //
CREATE DEFINER=`root`#`localhost` FUNCTION `testP`()
RETURNS int(11)
LANGUAGE SQL
NOT DETERMINISTIC
MODIFIES SQL DATA
SQL SECURITY DEFINER
COMMENT ''
BEGIN
DELETE FROM test2;
return 1;
END //
Now you can call this function in SELECT :
SELECT id, name, message FROM messages WHERE id = NULL OR testP()
(id = NULL - always NULL(FALSE), so testP() always gets executed.

It depends on the DBMS connector you are using. Most of the time your scenario should not be possible, but under certain circumstances it could work. For further details you should take a look at chapter 4 and 5 from the Blackhat-Paper Advanced MySQL Exploitation.

Yes it's possible.
$_GET['q'] would hold 1; DELETE FROM users; --
SELECT id, name, message FROM messages WHERE id = 1; DELETE FROM users; -- whatever here');

Related

Save MySql 'Show' result in db

So I'm kind of stumped.
I have a MySql project that involves a database table that is being manipulated and altered by scripts on a regular basis. This isn't so unusual, but I need to automate a script to run (after hours, when changes aren't happening) that would save the result of the following:
SHOW CREATE TABLE [table-name];
This command generates the ready-to-run script that would create the (empty) table in it's current state.
In SqlWorkbench and Navicat it displays the result of this SHOW command in a field in a result set, as if it was the result of a SELECT statement.
Ideally, I want to take into a variable in a procedure, and change the table name; adding a '-mm-dd-yyyy' to end of it, so I could show the day-to-day changes in the table schema on an active server.
However, I can't seem to be able to do that. Unlike a Select result set, I can't use it like that. I can't get it in a variable, or save it to a temporary, or physical table or anything. I even tried to return this as a value in a function, from which I got the error that a function cannot return a result set - which explains why it's displayed like one in the db clients.
I suspect that this is a security thing in MySql? If so, I can totally understand why and see the dangers exposed to a hacker, but this isn't a public-facing box at all, and I have full root/admin access to it. Hopefully somebody has already tackled this problem before.
This is on MySql 8, btw.
[Edit] After my first initial comments, I need to add; I'm not concerned about the data with this question whatsoever, but rather just these schema changes.
What I'd really -like- to do is this:
SELECT `Create Table` FROM ( SHOW CREATE TABLE carts )
But this seems to be mixing apples and oranges, as SHOW and SELECT aren't created equal, although they both seem to return the same sort of object
You cannot do it in the MySQL stored procedure language.
https://dev.mysql.com/doc/refman/8.0/en/show.html says:
Many MySQL APIs (such as PHP) enable you to treat the result returned from a SHOW statement as you would a result set from a SELECT; see Chapter 29, Connectors and APIs, or your API documentation for more information. In addition, you can work in SQL with results from queries on tables in the INFORMATION_SCHEMA database, which you cannot easily do with results from SHOW statements. See Chapter 26, INFORMATION_SCHEMA Tables.
What is absent from this paragraph is any mention of treating the results of SHOW commands like the results of SELECT queries in other contexts. There is no support for setting a variable to the result of a SHOW command, or using INTO, or running SHOW in a subquery.
So you can capture the result returned by a SHOW command in a client programming language (Java, Python, PHP, etc.), and I suggest you do this.
In theory, all the information used by SHOW CREATE TABLE is accessible in the INFORMATION_SCHEMA tables (mostly TABLES and COLUMNS), but formatting a complete CREATE TABLE statement is a non-trivial exercise, and I wouldn't attempt it. For one thing, there are new features in every release of MySQL, e.g. new data types and table options, etc. So even if you could come up with the right query to produce this output, in a couple of years it would be out of date and it would be a thankless code maintenance chore to update it.
The closest solution I can think of, in pure MySQL, is to regularly clone the table structure (no data), like so:
CREATE TABLE backup_20220618 LIKE my_table;
As far as I know, to get your hands on the full explicit CREATE TABLE statement, as a string, would require the use of an external tool like mysqldump which was designed specifically for that purpose.

Mysql Workbench - The best way to organize running frequently used SQL queries while development

I'm a java dev who uses Mysql Workbench as a database client and IntelliJ IDEA as an IDE. Every day I do SQL queries to the database from 5 up to 50 times a day.
Is there a convenient way to save and re-run frequently used queries in Mysql Workbench/IntelliJ IDEA so that I can:
avoid typing a full query which has already been used again
smoothly access a list of queries I've already used (e.g by auto-completion)
If there is no way to do it using Mysql Workbench / IDEA, could you please advise any good tools providing this functionality?
Thanks!
Create Stored Procedures, one per query (or sequence of queries). Give them short names (to avoid needing auto-completion).
For example, to find out how many rows in table foo (SELECT COUNT(*) FROM foo;).
One-time setup:
DELIMITER //
CREATE PROCEDURE foo_ct
BEGIN;
SELECT COUNT(*) FROM foo;
END //
DELIMITER ;
Usage:
CALL foo_ct();
You can pass arguments in in order to make minor variations. Passing in a table name is somewhat complex, but numbers of dates, etc, are practical and probably easy.
If you have installed SQLyog for your mysql then you can use Favorites menu option in which you can save your query and in one click it will automatically writes the saved query on Query Editor.
The previous answers are correct - depending on the version of the Query Browser they are either called Favorites or Snippets - the problem being you can't create sub-folders to group them. And keeping tabs open is an option - but sometimes the browser 'dies' - and you're back to ground 0. So the obvious solution I came up with - create a database table! I have a few 'metadata' fields for descriptions - the project a query is associated to; problem the query solves; and the actual query.
You could keep your query library in an SQL file and load that when WB opens (it's automatically opened when you restart WB and that file was open on last close). When you want to run a specific query place the caret in it's text and press Ctrl+Enter (Cmd+Enter on Mac) to run only this query. The organization of that SQL file is totally up to you. You have more freedom than any "favorites" solution can give you. You can even have more than one file with grouped statements.
Additionally, MySQL Workbench has a query history (see the Output Tab), which is saved to disk, so you can return to a query even month's after you wrote it.

Parameterized OLEDB source query

I am creating an ETL in SSIS in which I which I want my data source to be a restricted query, like select * from table_name where id='Variable'. This variable is what I defined as User created variable.
I do not understand how I can have my source query interact with the SSIS scoped Variable.
The only present options are
Table
Table from variable
SQL Command
SQL command from a variable
What I want is to have a SQL statement having a variable as parameter
Simple. Choose SQL command as the Data Access Mode. Enter your query with a question mark as a parameter placeholder. Then click the Parameters button and map your variable to Parameter0 in the Set Query Parameters dialog:
More information is available on MSDN.
An inferior alternative to #Edmund's approach is to use an Expression on another Variable to build your string. Assuming you have #[User::FirstName] already defined, you would then create another variable, #[User::SourceQuery].
In the properties for this variable, set EvaluateAsExpression to True and then set an Expression like "SELECT FirstName, LastName, FROM Person.Person WHERE FirstName = '" + #[User::FirstName] +"'" The double quotes are required because we are building an SSIS String.
There are two big reasons this approach should not be implored.
Caching
This approach is going to bloat your plan cache in SQL Server with N copies of essentially the same query. The first time it runs and the value is "Edmund" SQL Server will create an execution plan and save it (because it can be expensive to build them). You then run the package and the value is "Bill". SQL Server checks to see if it has a plan for this. It doesn't, it only has one for Edmund and so it creates another copy of the plan, this time hard coded to Bill. Lather-rinse-repeat and watch your available memory dwindle until it unloads some plans.
By using the parameter approach, when the plan is submitted to SQL Server, it should be creating a parameterized version of the plan internally and assumes that all parameters supplied will result in equal costing executions. Generally speaking, this is the desired behaviour.
If your database is optimized for ad-hoc workload (it's a setting turned off by default), that should be mitigated as every plan is going to get parameterized.
SQL Injection
The other big nasty you will run into with building your own string is that you open yourself up to SQL Injection attacks or at the least, you can get runtime errors. It's as simple as having a value of "d'Artagnan." That single quote will cause your query to fail resulting in package failure. Changing the value to "';DROP TABLE Person.Person;--" will result in great pain.
You might think it's trivial to safe quote everything but the effort of implementing it consistently everywhere you query is beyond what your employer is paying you. All the more so since there is native functionality provided to do the same thing.
When using OLEDB Connection manager (with SQL Server Native Client 11.0 provider in my case) you can catch an error like this:
Parameters cannot be extracted from the SQL command. The provider
might not help to parse parameter information from the command. In
that case, use the "SQL command from variable" access mode, in which
the entire SQL command is stored in a variable.
So you need to explicitly specify database name in OLEDB Connection manager properties. Otherwise SQL Server Native Client can use different database name then you mean (e.g. master in MSSQL Server).
For some cases you can explicitly specify database name for each database object used in query, e.g.:
select Name
from MyDatabase.MySchema.MyTable
where id = ?

SQL Server sp_help : how to limit the number of output windows

Normally successful execution of
sp_help [object_name]
in SQL Server returns a total of 7 output windows with various results out of which normally I am interested in only 2 windows namely the one with all the column information and the one with the constraints.
Is there a way I can tell SQLserver to only display these while formulating the command?
Short answer: no, you can't do this directly because the procedure is written to return that data, and TSQL has no mechanism for accessing specific result sets.
Long answer: but you can easily get the same information from other procedures or directly from the system catalog:
sp_columns, sp_helpconstraint (this is actually called by sp_help) etc.
sys.columns, sys.objects etc.
There's also the option of copying the source code from sp_help and using it as the basis of a new procedure that you create yourself, although personally I would just write it myself from scratch. If you do decide to write your own stored proc, you might find this question relevant too.

Default database for MySQL

Is there a way to allocate a default database to a specific user in MySQL so they don't need to specify the database name while making a query?
I think you need to revisit some concepts - as Lmwangi points out if you are connecting with mysql client then my.cnf can set it.
However, your use of the word query suggests that you are talking about connecting from some programming environment - in this case you will always need a connection object. To create connection object and in this case having default database to connect to will lead to no improvement (in terms of speed or simplicity). Efficiently managing your connection(s) might be interesting for you - but for this you should let us know exactly what is your environment.
If you use a database schema you don't need to specify the database name every time, but you need to select the database name.
The best thing to do would be to use a MySQL trigger on the connection. However, MySQL only accepts triggers for updates, deletes and inserts. A quick Google search yielded an interesting stored procedure alternative. Please
see MySQL Logon trigger.
When you assign the permissions to every user group, you can also specify, at the same file, several things for that group, for example the database that users group need to use.
You can do this with a specification file, depending on the language you are working with, as a simple variable. Later, you only have to look for that variable to know which database you need to work with. But, I repeat, it depends on the language. The specification file can be an XML, phpspecs file, or anything like this.