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Merge pull request #92 from grakic/gh-pages_input-filtering-2

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Minor fixes for Data Filtering section
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Phil Sturgeon
2012-07-12 06:03:11 -07:00
parent 236c9e4656 e8bd3abcce
commit 1ce0244683
1 changed files with 7 additions and 7 deletions
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_posts/07-04-01-Data-Filtering.md
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@@ -11,25 +11,25 @@ PHP functions `filter_var` and `filter_input` can sanitize text and validate tex
email addresses).
Foreign input can be anything, from `$_GET` and `$_POST` form input data, some values in `$_SERVER`,
the HTTP body via `fopen('php://input', 'r')`, etc are all considered foriegn inputs. It is not
the HTTP body via `fopen('php://input', 'r')`, etc are all considered foreign inputs. It is not
limited to form data submitted by the user, both uploaded and downloaded files, session values and
cookies count too.
cookies count too. Data from third party web services should also be considered foreign input.
While foreign data can be stored, combined and accessed later, it is still a foreign input. Every
time you process, output, concatenate or include some data in your code you should ask yourself if
the data is filtered properly and can it be trusted.
Filtering is tailored to the specific data usage. For example, when including foreign input is passed
Filtering is tailored to the specific data usage. For example, when foreign input is passed
to a HTML page output it can execute HTML and JavaScript on your site! This is known as Cross-Site
Scripting (XSS) and can be a very dangerous attack. One way to avoid this is to sanitize all HTML tags
in the input, or encode them.
in the input, removing tags or escaping them.
That is of course one instance of filtering against a specific type of attach. Another example would be
when passing options to be executed on the command line. This can be extremely dangers and is usually bad
when passing options to be executed on the command line. This can be extremely dangerous and is usually bad
idea, but you can use the built-in `escapeshellarg` function to sanitize the arguments.
One last example would be accepting foreign input to determine a file to load. This could be expoited by
changing the filename to a file path, so you need to remove and / from the path, so it cant load potentially
changing the filename to a file path, so you need to remove / or other characters from the path, so it cant load potentially
hidden or sensitive files.
For performance, you can store filtered data and have it ready for usage next time. Just remember