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While sanitizing and escaping everything is very important when dealing with websites, I think there are times when we need to back off a little bit, and trust the functions that have been given to us by WordPress.
<a href="<?php echo esc_url( get_permalink( get_the_ID() ) ); ?>" title="<?php echo esc_attr( sprintf( __( 'Permanent Link to %s', 'domain' ), the_title_attribute( array( 'echo' => false ) ) ) ); ?>" >
I call that paranoia (and I see it in a lot of themes.) Dirty, difficult to read and understand, and even more difficult to spot an error. The permalink and the title attribute are never going to break out of the attributes syntax and escaping them a billion times doesn’t really help. Here’s a cleaner version for comparison:
<a href="<?php the_permalink(); ?>" title="<?php the_title_attribute( array( 'before' => __( 'Permanent link to ', 'domain' ) ) ); ?>" >
Quite straightforward and easy to understand. You don’t even need to worry about escaping the “before” text, because
the_title_attribute will escape it for you. One might argue that explicit escaping (right at the output) is more secure than implicit escaping, but since functions prefixed with
the_ are meant for output, I tend to trust their output. You just need to know where each one should go.
With that said, if you have a super hi-jacked WordPress installation with a malicious plugin overwriting the output of the functions mentioned above, there’s really not much you can do. Even if you triple espace with
get_permalink, a plugin might just filter in on
post_link and output whatever it needs to output by-passing all escaping.