Security.php

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<?php
namespace Magento\Framework\Xml;

use DOMDocument;

class Security
{
    private function heuristicScan($xmlContent)
    {
        return strpos($xmlContent, '<!ENTITY') === false;
    }

    private function isPhpFpm()
    {
        return substr(php_sapi_name(), 0, 3) === 'fpm';
    }

    public function scan($xmlContent)
    {
        if ($this->isPhpFpm()) {
            return $this->heuristicScan($xmlContent);
        }

        $document = new DOMDocument();

        $loadEntities = libxml_disable_entity_loader(true);
        $useInternalXmlErrors = libxml_use_internal_errors(true);

        set_error_handler(
            function ($errno, $errstr) {
                if (substr_count($errstr, 'DOMDocument::loadXML()') > 0) {
                    return true;
                }
                return false;
            },
            E_WARNING
        );

        $result = (bool)$document->loadXML($xmlContent, LIBXML_NONET);
        restore_error_handler();
        // Entity load to previous setting
        libxml_disable_entity_loader($loadEntities);
        libxml_use_internal_errors($useInternalXmlErrors);

        if (!$result) {
            return false;
        }

        foreach ($document->childNodes as $child) {
            if ($child->nodeType === XML_DOCUMENT_TYPE_NODE) {
                if ($child->entities->length > 0) {
                    return false;
                }
            }
        }

        return true;
    }
}