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authormarcus <marcus@36083f99-b078-4883-b0ff-0f9b5a30f544>2009-04-17 15:41:16 +0000
committermarcus <marcus@36083f99-b078-4883-b0ff-0f9b5a30f544>2009-04-17 15:41:16 +0000
commit07155a084db111c0586ce7ed958c87eed6116704 (patch)
treee5e64cd58d20bdb2a0ad896403d8814f11018f52 /vendors/kses/docs/attribute-value-checks
parent566de88eb3a15b58600f5195dc7b185b8aae0d41 (diff)
downloadelgg-07155a084db111c0586ce7ed958c87eed6116704.tar.gz
elgg-07155a084db111c0586ce7ed958c87eed6116704.tar.bz2
Closes #833: Kses now built as module
git-svn-id: https://code.elgg.org/elgg/trunk@3222 36083f99-b078-4883-b0ff-0f9b5a30f544
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-kses attribute value checks
-===========================
-
-As you've probably already read in the README file, an $allowed_html array
-normally looks like this:
-
-$allowed = array('b' => array(),
- 'i' => array(),
- 'a' => array('href' => 1,
- 'title' => 1),
- 'p' => array('align' => 1),
- 'br' => array());
-
-This sets what elements and attributes are allowed.
-
-From kses 0.2.0, you can also perform some checks on the attribute values. You
-do it like this:
-
-$allowed = array('b' => array(),
- 'i' => array(),
- 'a' => array('href' =>
- array('maxlen' => 100),
- 'title' => 1),
- 'p' => array('align' => 1),
- 'font' => array('size' =>
- array('maxval' => 20)),
- 'br' => array());
-
-This means that kses should perform the maxlen check with the value 100 on the
-<a href=> value, as well as the maxval check with the value 20 on the <font
-size=> value.
-
-The currently implemented checks (with more to come) are 'maxlen', 'maxval',
-'minlen', 'minval' and 'valueless'.
-
-'maxlen' checks that the length of the attribute value is not greater than the
-given value. It is helpful against Buffer Overflows in WWW clients and various
-servers on the Internet. In my example above, it would mean that
-"<a href='ftp://ftp.v1ct1m.com/AAAA..thousands_of_A's...'>" wouldn't be
-accepted.
-
-Of course, this problem is even worse if you put that long URL in a <frame>
-tag instead, so the WWW client will fetch it automatically without a user
-having to click it.
-
-'maxval' checks that the attribute value is an integer greater than or equal to
-zero, that it doesn't have an unreasonable amount of zeroes or whitespace (to
-avoid Buffer Overflows), and that it is not greater than the given value. In
-my example above, it would mean that "<font size='20'>" is accepted but
-"<font size='21'>" is not. This check helps against Denial of Service attacks
-against WWW clients.
-
-One example of this DoS problem is <iframe src="http://some.web.server/"
-width="20000" height="2000">, which makes some client machines completely
-overloaded.
-
-'minlen' and 'minval' works the same as 'maxlen' and 'maxval', except that they
-check for minimum lengths and values instead of maximum ones.
-
-'valueless' checks if an attribute has a value (like <a href="blah">) or not
-(<option selected>). If the given value is a "y" or a "Y", the attribute must
-not have a value to be accepted. If the given value is an "n" or an "N", the
-attribute must have a value. Note that <a href=""> is considered to have a
-value, so there's a difference between valueless attributes and attribute
-values with the length zero.
-
-You can combine more than one check, by putting one after the other in the
-inner array.