Do you only run htmlspecialchars() on output or is there other functionality you also do?

Question

When outputting user input, do you only use htmlspecialchars() or are there are functions/actions/methods you also run? I'm looking for something that will also deal with XSS.

I'm wondering if I should write a function that escapes user input on output or just use htmlspecialchars(). I'm looking for the generic cases, not the specific cases that can be dealt with individually.

Answer 1

I usually use

htmlspecialchars($var, ENT_QUOTES) 

on input fields. I created a method that does this because i use that a lot and it makes the code shorter and more readable.

Answer 2

Lets have a quick review of WHY escaping is needed in different contexts:

If you are in a quote delimited string, you need to be able to escape the quotes. If you are in xml, then you need to separate "content" from "markup" If you are in SQL, you need to separate "commands" from "data" If you are on the command line, you need to separate "commands" from "data"

This is a really basic aspect of computing in general. Because the syntax that delimits data can occur IN THE DATA, there needs to be a way to differentiate the DATA from the SYNTAX, hence, escaping.

In web programming, the common escaping cases are: 1. Outputting text into HTML 2. Outputting data into HTML attributes 3. Outputting HTML into HTML 4. Inserting data into Javascript 5. Inserting data into SQL 6. Inserting data into a shell command

Each one has a different security implications if handled incorrectly. THIS IS REALLY IMPORTANT! Let's review this in the context of PHP:

1. Text into HTML: htmlspecialchars(...)

2. Data into HTML attributes htmlspecialchars(..., ENT_QUOTES)

3. HTML into HTML Use a library such as HTMLPurifier to ENSURE that only valid tags are present.

4. Data into Javascript I prefer json_encode. If you are placing it in an attribute, you still need to use #2, such as

5. Inserting data into SQL Each driver has an escape() function of some sort. It is best. If you are running in a normal latin1 character set, addslashes(...) is suitable. Don't forget the quotes AROUND the addslashes() call:

   "INSERT INTO table1 SET field1 = '" . addslashes($data) . "'"

6. Data on the command line escapeshellarg() and escapeshellcmd() -- read the manual

-- Take these to heart, and you will eliminate 95%* of common web security risks! (* a guess)