All browser-bound outputs of add_query_arg() or remove_query_arg() must be sanitized with attribute_escape()

[markjaquith]

The add_query_arg() and remove_query_arg() functions do not generate XSS-proof URLs by default (because their output can also be used to redirect to the resultant URL). But all browser-bound outputs of these functions must be sanitized before being echoed. attribute_escape() is the function that escapes content used in attributes (and URLs are almost always used in attributes, like <a href="<?php echo attribute_escape(add_query_arg('foo', 'value', $initial_url)); ?>">link</a> )

XSS exploits have been tied to this vulnerability:

•  http://secunia.com/advisories/24430/

Triple milestone here:

• trunk
• 2.0.x
• 2.1.x

Patch for entire /wordpress/ family

(In [5007]) Sanitize browser-bound add_query_arg() outputs. fixes #3937