Sanitizes a string and removed disallowed URL protocols.

Description

This function removes all non-allowed protocols from the beginning of the string. It ignores whitespace and the case of the letters, and it does understand HTML entities. It does its work recursively, so it won’t be fooled by a string like javascript:javascript:alert(57).

Parameters

$contentstringrequired

Content to filter bad protocols from.

$allowed_protocolsstring[]required

Array of allowed URL protocols.

Return

Source

function wp_kses_bad_protocol( $content, $allowed_protocols ) {
	$content = wp_kses_no_null( $content );

	// Short-circuit if the string starts with `https://` or `http://`. Most common cases.
	if (
		( str_starts_with( $content, 'https://' ) && in_array( 'https', $allowed_protocols, true ) ) ||
		( str_starts_with( $content, 'http://' ) && in_array( 'http', $allowed_protocols, true ) )
	) {
		return $content;
	}

	$iterations = 0;

	do {
		$original_content = $content;
		$content          = wp_kses_bad_protocol_once( $content, $allowed_protocols );
	} while ( $original_content !== $content && ++$iterations < 6 );

	if ( $original_content !== $content ) {
		return '';
	}

	return $content;
}

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