How to stop BB Code manipulation?

Question

Hi I recently discovered an issue where people using BB Code to enter links are able to manipulate them.

They are meant to enter something like:

[LINK]http://www.domain.com[/LINK]

However they can enter something like this to make the link color red:

[LINK]http://www.domain.com 'span style="color:red;"'[/LINK]

This is the code which converts it:

$text = preg_replace("/\\[LINK\\\](.*?)\\[\/LINK\\]/is",
                       "<a href='$1' target='_blank'>$1</a>", $text);

Also, I forgot, this is the other type:

[LINK=http://www.domain.com]example text[/LINK]

$text = preg_replace("/\\[LINK\=(.*?)\\\](.*?)\\[\/LINK\\]/is",
                       "<a href='$1' target='_blank'>$2</a>", $text);

Answer 1

Don't allow quotes and such in the url, and strip tags which failed in the first pass:

$text = preg_replace("/\[LINK\]([^'\"\\s]*?)\[\/LINK\]/is",
                               "<a href='$1' target='_blank'>$1</a>", $text);

$text = preg_replace("/\[LINK\](.*?)\[\/LINK\]/is", "<i>(link removed)</i>", $text);