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WP_Query::parse_query() does not handle invalid query arg values #12738

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WP_Query::parse_query() does not handle invalid query arg values #12738

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29 changes: 29 additions & 0 deletions src/wp-includes/class-wp.php
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,17 @@ class WP {
*/
public $private_query_vars = array( 'offset', 'posts_per_page', 'posts_per_archive_page', 'showposts', 'nopaging', 'post_type', 'post_status', 'category__in', 'category__not_in', 'category__and', 'tag__in', 'tag__not_in', 'tag__and', 'tag_slug__in', 'tag_slug__and', 'tag_id', 'post_mime_type', 'perm', 'comments_per_page', 'post__in', 'post__not_in', 'post_parent', 'post_parent__in', 'post_parent__not_in', 'title', 'fields' );

/**
* Public query variables that only ever hold a single value.
*
* These are query variables that will hit a fatal error if they are given an
* array instead of a single value.
*
* @since 7.1.0
* @var string[]
*/
private $single_value_query_vars = array( 'feed' );

@peterwilsoncc peterwilsoncc Jul 30, 2026

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I'd make this public to allow theme and plugin authors to do either of two things:

  • Add to the list, eg an SEO plugin may wish to add their sitemap query var to the list
  • Remove from the list, WP_Query is pretty flexible and a plugin might make use of the various filters to modified valid query vars and modify the SQL query accordingly


/**
* Extra query variables set by the user.
*
Expand Down Expand Up @@ -353,6 +364,24 @@ public function parse_request( $extra_query_vars = '' ) {
}
}

/*
* Check against the list of variables that will fatal if given an array instead
* of a single value. If we hit that condition, we end processing the request
* immediately.
*/
foreach ( $this->single_value_query_vars as $wpvar ) {
if (
isset( $this->query_vars[ $wpvar ] )
&& ! is_scalar( $this->query_vars[ $wpvar ] )
) {
wp_die(
__( 'Invalid value for a query variable.' ),
__( 'Error, this request could not be processed.' ),
400
);
Comment on lines +377 to +381
Comment on lines +377 to +381

@peterwilsoncc peterwilsoncc Jul 30, 2026

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What do you think of triggering a 404 if the URL has been messed around with?

Arguably /?feed[]=rss&feed[]=atom doesn't exist and this would trigger the website's theme appropriate 404 page rather than the generically designed wp_die() error messaging.

Suggested change
wp_die(
__( 'Invalid value for a query variable.' ),
__( 'Error, this request could not be processed.' ),
400
);
$this->query_vars['error'] = 404;
unset( $this->query_vars[ $wpvar ] );

}
}

// Convert urldecoded spaces back into '+'.
foreach ( get_taxonomies( array(), 'objects' ) as $taxonomy => $t ) {
if ( $t->query_var && isset( $this->query_vars[ $t->query_var ] ) ) {
Expand Down
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