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Escaping strings for MySQL

From: PHP with MySQL Essential Training

Video: Escaping strings for MySQL

We learned about SQL injection in the last movie, in this movie we're going to learn what to do about it. As we saw, the biggest problem comes from having a single quote in the data that you want to include in your SQL. The way to solve that is to escape the single quote, that is to tell MySQL this is not the single quote that ends the string, this is just part of the string. And the way we escape it, give it that special meaning to MySQL, is that so we put a back slash before single quotes. So for example, if we had today's widget trivia, we just simply put a back slash in front of the single quote and then it'll be fine. It'll be put into our string, MySQL will look at it, and when it gets to that backslash it will say oh, the next character has special behavior. This is not the ending single quote, this is just a single quote and then it will keep going from there until it gets to the real ending single quote. Now, it's not very practical for us to always put in backslashes by hand, which is what we would be doing here.

Escaping strings for MySQL

We learned about SQL injection in the last movie, in this movie we're going to learn what to do about it. As we saw, the biggest problem comes from having a single quote in the data that you want to include in your SQL. The way to solve that is to escape the single quote, that is to tell MySQL this is not the single quote that ends the string, this is just part of the string. And the way we escape it, give it that special meaning to MySQL, is that so we put a back slash before single quotes. So for example, if we had today's widget trivia, we just simply put a back slash in front of the single quote and then it'll be fine. It'll be put into our string, MySQL will look at it, and when it gets to that backslash it will say oh, the next character has special behavior. This is not the ending single quote, this is just a single quote and then it will keep going from there until it gets to the real ending single quote. Now, it's not very practical for us to always put in backslashes by hand, which is what we would be doing here.

Instead, what we need is a function that will do that for us. We need some way that we can just tell it whatever the data is, whether it's data that came in from a form, whether it was pulled from a database, we want to run our function on it to escape all the values that might be in there. PHP offers us something like that, it's called add slashes. And addslashes will go through our string and add the backslash in front of those characters. Now there's a little bit of PHP history that we should go into here. People thought addslashes ($string) was a great idea. And that it was such a great idea that it ought to be a default in order to keep new developers who were just learning PHP from making this very common, very tragic mistake.

So they decided to build it in as a default with something called Magic Quotes. So PHP would automatically call addslashes, and all GET, POST, and COOKIE data. And that would at least make sure that we were protected from the outside SQL injection coming in automatically. It was added way back in PHP 2, it became the default as of PHP 3, but it was finally removed in PHP 5.4. Why was it removed? Well, because it caused a lot of problems. It was a real big headache for developers. And the biggest reason was that magic quotes could be turned on or off.

So some people liked to have it on or unknowingly had it on so that it was doing this for them. Other people turned it off. And then did they adding the slashes themselves. So then if you had a PHP application that was developed on one machine, it wasn't portable to another machine anymore. Because that other machine might be adding slashes itself, or it might not be adding the slashes when you were expecting them to be there. So it started causing lots and lots of problems. So finally, they removed it, and they removed it in favor of something better. Something that you aught to be using instead of add slashes, which is real escape string. The idea of real escape string first came about in PHP 4.3 with the MySQL database API.

However, when MySQLi came out, that's the version in PHP5, and that's the one that we're going to be using. So MySQLi, real escape string is going to escape the string in a way that's appropriate for MySQLi. That's what it does, it's database sensitive. So, it knows alright, for the MySQL database, here's the things that need to be escaped. So that's the one that we're going to be using, and using it is very easy. Let's see how. So, to begin with, let's open up database's insert and let's do our work in here. You see where we had our insert before.

Right now we're just taking the value that came in from menu name and just dropping it right in here for our values. So, if we try to create a new subject called Today's Widget Trivia, we'll get a problem. As soon as this gets dropped in down here, this single quote is going to cause us a problem. We could escape it by hand, but that's not useful; instead we want to use one of our functions. And so we're going to use that MySQLi real escape string. So, let's imagine these came in from POST variables. So, we're not going to mess with them, we're going to leave them exactly as they are. This is what came in from the POST. But once we get it, then we're going to escape it. So, what we'll do is menu_name equals the result of mysqli_real_escape_string. Now, the values that we provide to this, the two arguments. The first one is going to be the connection to the database, and then the second one is going to be the old value, menu_name.

Now I've got he same old name and new name, that's fine. It's no big deal. It's going to take what was the old name and put it in, and the output will just replace it. So it'll be got at that point. Now, if you were used to using the MySQL real escape string version, these arguments are flipped. It's the reverse. And that's true for a lot of the MySQLi functions, they reverse the order of the arguments. So, that's it, that's all there is to being able to do this. It's really that easy. It's just a matter of remembering to escape it, before you include it down here. So, let's save it and let's go try it. Let's go to Firefox, here's our pages.

Now reload, that's the pages I have. And now we'll do our insert. And I have my new value up there. Go back and reload the page. There it is, Today's Widget Trivia. You see, it submitted that with no problem whatsoever. And that's because we used real escape string. So, what about position and visible? Well, you don't really need to escape anything that's not a string. It's real escape string, that's what it's for. It's designed for strings. I'll make a note here, escape all strings. You don't need to escape the integers, they're not going to go inside single quotes here. In fact, it's a good idea, not to use single quotes around it for exactly that reason.

So it won't cause that problem. In addition, you can take the additional step of just making sure that this is an integer. That will just make sure that it's typecast as an integer, and then will make sure that, that's what gets used here. So you can do that additional step if you want to check, but you don't need to call real escape string on it. So what kinds of things should you be escaping then? Well, you should not trust anything, anything that comes in from a user. Whether it's from the URL string, whether it's a form value, a cookie value, even your database values which may have originated from somewhere else, from some user somewhere else.

We also need to escape because they may have innocent little single quotes in them like this, we may not be thinking about. So we always want to use anything that we're going to construct into our MySQL into a string, needs to have real escape string. The one thing you don't want to real escape is something that has already been escaped. You don't want to escape it twice. Just make sure you only escape it once right before you use it. Now, we've mostly been talking about the single quote, it's worth noting that it does actually change a few other characters as well. There's a special ASCII character that represents null, there's some line return characters.

Things like that that also get changed at the same time, it's not just the single quote. But the single quote is the most important one, and the one we care the most about. So it's that easy, there's no excuse for not protecting your database from SQL injection by using MySQLi real escape string.

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This video is part of

Image for PHP with MySQL Essential Training
PHP with MySQL Essential Training

131 video lessons · 34174 viewers

Kevin Skoglund
Author

 
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  1. 4m 8s
    1. Welcome
      1m 0s
    2. Using the exercise files
      3m 8s
  2. 15m 6s
    1. What is PHP?
      3m 52s
    2. The history of PHP
      2m 51s
    3. Why choose PHP?
      4m 10s
    4. Installation overview
      4m 13s
  3. 54m 53s
    1. Overview
      2m 33s
    2. Working with Apache Web Server
      6m 56s
    3. Changing the document root
      7m 24s
    4. Enabling PHP
      6m 16s
    5. Upgrading PHP
      3m 30s
    6. Configuring PHP
      10m 3s
    7. Installing MySQL
      5m 46s
    8. Configuring MySQL
      7m 24s
    9. Text editor
      5m 1s
  4. 31m 25s
    1. Overview
      3m 27s
    2. Installing WampServer
      5m 46s
    3. Finding the document root
      2m 24s
    4. Configuring PHP
      8m 12s
    5. Configuring MySQL
      5m 45s
    6. Text editor
      5m 51s
  5. 19m 12s
    1. Embedding PHP code on a page
      6m 43s
    2. Outputting dynamic text
      5m 55s
    3. The operational trail
      2m 27s
    4. Inserting code comments
      4m 7s
  6. 1h 18m
    1. Variables
      7m 50s
    2. Strings
      4m 38s
    3. String functions
      8m 54s
    4. Numbers part one: Integers
      6m 27s
    5. Numbers part two: Floating points
      5m 25s
    6. Arrays
      10m 0s
    7. Associative arrays
      6m 37s
    8. Array functions
      6m 33s
    9. Booleans
      3m 50s
    10. NULL and empty
      5m 15s
    11. Type juggling and casting
      8m 27s
    12. Constants
      4m 43s
  7. 27m 37s
    1. If statements
      6m 0s
    2. Else and elseif statements
      4m 16s
    3. Logical operators
      7m 30s
    4. Switch statements
      9m 51s
  8. 42m 15s
    1. While loops
      8m 41s
    2. For loops
      5m 59s
    3. Foreach loops
      8m 16s
    4. Continue
      8m 28s
    5. Break
      4m 8s
    6. Understanding array pointers
      6m 43s
  9. 37m 25s
    1. Defining functions
      8m 25s
    2. Function arguments
      5m 32s
    3. Returning values from a function
      7m 33s
    4. Multiple return values
      4m 53s
    5. Scope and global variables
      6m 2s
    6. Setting default argument values
      5m 0s
  10. 20m 18s
    1. Common problems
      3m 47s
    2. Warnings and errors
      8m 36s
    3. Debugging and troubleshooting
      7m 55s
  11. 57m 57s
    1. Links and URLs
      5m 33s
    2. Using GET values
      5m 35s
    3. Encoding GET values
      8m 41s
    4. Encoding for HTML
      9m 26s
    5. Including and requiring files
      7m 40s
    6. Modifying headers
      6m 45s
    7. Page redirection
      6m 43s
    8. Output buffering
      7m 34s
  12. 1h 3m
    1. Building forms
      7m 28s
    2. Detecting form submissions
      5m 59s
    3. Single-page form processing
      7m 57s
    4. Validating form values
      10m 40s
    5. Problems with validation logic
      9m 54s
    6. Displaying validation errors
      7m 23s
    7. Custom validation functions
      6m 28s
    8. Single-page form with validations
      7m 25s
  13. 28m 5s
    1. Working with cookies
      2m 49s
    2. Setting cookie values
      5m 55s
    3. Reading cookie values
      6m 1s
    4. Unsetting cookie values
      4m 51s
    5. Working with sessions
      8m 29s
  14. 48m 39s
    1. MySQL introduction
      6m 43s
    2. Creating a database
      7m 41s
    3. Creating a database table
      7m 42s
    4. CRUD in MySQL
      5m 48s
    5. Populating a MySQL database
      7m 32s
    6. Relational database tables
      6m 40s
    7. Populating the relational table
      6m 33s
  15. 56m 4s
    1. Database APIs in PHP
      4m 51s
    2. Connecting to MySQL with PHP
      7m 45s
    3. Retrieving data from MySQL
      8m 47s
    4. Working with retrieved data
      6m 12s
    5. Creating records with PHP
      6m 58s
    6. Updating and deleting records with PHP
      9m 6s
    7. SQL injection
      3m 5s
    8. Escaping strings for MySQL
      6m 45s
    9. Introducing prepared statements
      2m 35s
  16. 35m 58s
    1. Blueprinting the application
      7m 19s
    2. Building the CMS database
      5m 14s
    3. Establishing your work area
      4m 38s
    4. Creating and styling the first page
      4m 22s
    5. Making page assets reusable
      6m 36s
    6. Connecting the application to the database
      7m 49s
  17. 32m 49s
    1. Adding pages to the navigation subjects
      5m 58s
    2. Refactoring the navigation
      6m 7s
    3. Selecting pages from the navigation
      6m 2s
    4. Highlighting the current page
      5m 26s
    5. Moving the navigation to a function
      9m 16s
  18. 1h 45m
    1. Finding a subject in the database
      9m 48s
    2. Refactoring the page selection
      10m 52s
    3. Creating a new subject form
      6m 55s
    4. Processing form values and adding subjects
      11m 20s
    5. Passing data in the session
      9m 16s
    6. Validating form values
      9m 40s
    7. Creating an edit subject form
      8m 30s
    8. Using single-page submission
      7m 44s
    9. Deleting a subject
      9m 44s
    10. Cleaning up
      10m 37s
    11. Assignment: Pages CRUD
      4m 30s
    12. Assignment results: Pages CRUD
      6m 10s
  19. 39m 26s
    1. The public appearance
      8m 52s
    2. Using a context for conditional code
      11m 37s
    3. Adding a default subject behavior
      6m 9s
    4. The public content area
      5m 51s
    5. Protecting page visibility
      6m 57s
  20. 1h 3m
    1. User authentication overview
      4m 3s
    2. Admin CRUD
      8m 41s
    3. Encrypting passwords
      7m 26s
    4. Salting passwords
      5m 42s
    5. Adding password encryption to CMS
      11m 54s
    6. New PHP password functions
      3m 13s
    7. Creating a login system
      11m 28s
    8. Checking for authorization
      5m 48s
    9. Creating a logout page
      5m 40s
  21. 2m 4s
    1. Next steps
      2m 4s

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