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I had to develop a Drupal 8 based website for a client. This client has a quite strict configuration for its firewall and filters the characters used in POST values. It happens to be a bit too restrictive on the contact form for the taste of the marketing department. The security team would consent to lift some character limitations if I could list them the measures used by Drupal and Webform to filter/sanitize user inputs.

I am pretty confident that Drupal does a good job in that regard. I expect a mixture of htmlentities(), filter_var(), custom functions calls and other related configurations but I couldn't find any details. All my searches on the subject spawns answers around the fact that Drupal does sanitize its input, but nothing concrete.

How does Drupal sanitize the user input?

  • The key thing to note, which Clive mentioned below, is that input is saved as-is, and is only filtered for output. – Jaypan Jun 26 '18 at 22:22
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Drupal uses Twig's autoescape feature, which in turn uses escape, which itself uses htmlspecialchars to prepare markup safe for output.

SafeMarkup::checkPlain() preceded the autoescaping (deprecated now), so you may see that used, and HTML::escape can be used if you need to do it manually for whatever reason.

As with all versions of Drupal, filtering is done on output only, not input, so filter_var and friends aren't involved.

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