Source

File: wp-admin/includes/class-wp-site-health-auto-updates.php

public function test_wp_version_check_attached() {
		if ( ! is_main_site() ) {
			return;
		}

		$cookies = wp_unslash( $_COOKIE );
		$timeout = 10;
		$headers = array(
			'Cache-Control' => 'no-cache',
		);
		/** This filter is documented in wp-includes/class-wp-http-streams.php */
		$sslverify = apply_filters( 'https_local_ssl_verify', false );

		// Include Basic auth in loopback requests.
		if ( isset( $_SERVER['PHP_AUTH_USER'] ) && isset( $_SERVER['PHP_AUTH_PW'] ) ) {
			$headers['Authorization'] = 'Basic ' . base64_encode( wp_unslash( $_SERVER['PHP_AUTH_USER'] ) . ':' . wp_unslash( $_SERVER['PHP_AUTH_PW'] ) );
		}

		$url = add_query_arg(
			array(
				'health-check-test-wp_version_check' => true,
			),
			admin_url( 'site-health.php' )
		);

		$test = wp_remote_get( $url, compact( 'cookies', 'headers', 'timeout', 'sslverify' ) );

		if ( is_wp_error( $test ) ) {
			return array(
				'description' => sprintf(
					/* translators: %s: Name of the filter used. */
					__( 'Could not confirm that the %s filter is available.' ),
					'<code>wp_version_check()</code>'
				),
				'severity'    => 'warning',
			);
		}

		$response = wp_remote_retrieve_body( $test );

		if ( 'yes' !== $response ) {
			return array(
				'description' => sprintf(
					/* translators: %s: Name of the filter used. */
					__( 'A plugin has prevented updates by disabling %s.' ),
					'<code>wp_version_check()</code>'
				),
				'severity'    => 'fail',
			);
		}
	}