Form simple action vs. more complicated

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You have a page called MyPage.php containing a form that is handled by the same page.
What is the difference when you simply define action like

HTML

action="MyPage.php"

and when you do it like

HTML

action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>"

and Which one is more secure?

Posted 16-Feb-15 5:44am

cs101000

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Thomas Daniels · Accepted Answer · 2015-02-16T06:08:00

Solution 1

The advantage of using PHP_SELF is that if you rename your page, your action attribute also changes.

About the security: with htmlspecialchars or htmlentities, they have the same security. But if you don't escape HTML characters with PHP_SELF, there are some exploits[^].

Personally, I suggest using $_SERVER["SCRIPT_NAME"]. If you update your filename, then the action attribute will update to, and with SCRIPT_NAME, you don't have the risk of the exploits with PHP_SELF.

Posted 16-Feb-15 6:08am

Thomas Daniels

Comments

Maciej Los 16-Feb-15 12:32pm

Nicely explained ;)

Thomas Daniels 16-Feb-15 12:51pm

Thank you!

cs101000 16-Feb-15 12:33pm

Do $_SERVER["SCRIPT_NAME"] and $_SERVER["PHP_SELF"] have the same return value? If yes why the latter is vulnerable to exploits?

Thomas Daniels 16-Feb-15 12:51pm

PHP_SELF is vulnerable in case someone sends this link to someone else:
http://yoursite/MyPage.php/"><b>test</b>
In that case, people who go to the link get to see a bold piece of text. That's pretty innocent, but it can also be used for script-tags. If you use SCRIPT_NAME, the action attribute will only consist of MyPage.php, not the other things.

cs101000 16-Feb-15 13:12pm

Thank you for the answer! So I don't need htmlspecialchars or htmlentities for $_SERVER["SCRIPT_NAME"] then, right?

Thomas Daniels 16-Feb-15 13:15pm

No, you don't need to escape HTML chars for SCRIPT_NAME.