Proyectos de Subversion Moodle

<?php

namespace PhpOffice\PhpSpreadsheet\Reader\Security;

use PhpOffice\PhpSpreadsheet\Reader;

class XmlScanner
{
    private const ENCODING_PATTERN = '/encoding\s*=\s*(["\'])(.+?)\1/s';
    private const ENCODING_UTF7 = '/encoding\s*=\s*(["\'])UTF-7\1/si';

    private string $pattern;

    /** @var ?callable */
    private $callback;

    public function __construct(string $pattern = '<!DOCTYPE')
    {
        $this->pattern = $pattern;
    }

    public static function getInstance(Reader\IReader $reader): self
    {
        $pattern = ($reader instanceof Reader\Html) ? '<!ENTITY' : '<!DOCTYPE';

        return new self($pattern);
    }

    public function setAdditionalCallback(callable $callback): void
    {
        $this->callback = $callback;
    }

    private static function forceString(mixed $arg): string
    {
        return is_string($arg) ? $arg : '';
    }

    private function toUtf8(string $xml): string
    {
        $charset = $this->findCharSet($xml);
        $foundUtf7 = $charset === 'UTF-7';
        if ($charset !== 'UTF-8') {
            $testStart = '/^.{0,4}\s*<?xml/s';
            $startWithXml1 = preg_match($testStart, $xml);
            $xml = self::forceString(mb_convert_encoding($xml, 'UTF-8', $charset));
            if ($startWithXml1 === 1 && preg_match($testStart, $xml) !== 1) {
                throw new Reader\Exception('Double encoding not permitted');
            }
            $foundUtf7 = $foundUtf7 || (preg_match(self::ENCODING_UTF7, $xml) === 1);
            $xml = preg_replace(self::ENCODING_PATTERN, '', $xml) ?? $xml;
        } else {
            $foundUtf7 = $foundUtf7 || (preg_match(self::ENCODING_UTF7, $xml) === 1);
        }
        if ($foundUtf7) {
            throw new Reader\Exception('UTF-7 encoding not permitted');
        }
        if (substr($xml, 0, Reader\Csv::UTF8_BOM_LEN) === Reader\Csv::UTF8_BOM) {
            $xml = substr($xml, Reader\Csv::UTF8_BOM_LEN);
        }

        return $xml;
    }

    private function findCharSet(string $xml): string
    {
        if (substr($xml, 0, 4) === "\x4c\x6f\xa7\x94") {
            throw new Reader\Exception('EBCDIC encoding not permitted');
        }
        $encoding = Reader\Csv::guessEncodingBom('', $xml);
        if ($encoding !== '') {
            return $encoding;
        }
        $xml = str_replace("\0", '', $xml);
        if (preg_match(self::ENCODING_PATTERN, $xml, $matches)) {
            return strtoupper($matches[2]);
        }

        return 'UTF-8';
    }

    /**
     * Scan the XML for use of <!ENTITY to prevent XXE/XEE attacks.
     *
     * @param false|string $xml
     */
    public function scan($xml): string
    {
        // Don't rely purely on libxml_disable_entity_loader()
        $pattern = '/\0*' . implode('\0*', mb_str_split($this->pattern, 1, 'UTF-8')) . '\0*/';

        $xml = "$xml";
        if (preg_match($pattern, $xml)) {
            throw new Reader\Exception('Detected use of ENTITY in XML, spreadsheet file load() aborted to prevent XXE/XEE attacks');
        }

        $xml = $this->toUtf8($xml);
        if (preg_match($pattern, $xml)) {
            throw new Reader\Exception('Detected use of ENTITY in XML, spreadsheet file load() aborted to prevent XXE/XEE attacks');
        }

        if ($this->callback !== null) {
            $xml = call_user_func($this->callback, $xml);
        }

        return $xml;
    }

    /**
     * Scan the XML for use of <!ENTITY to prevent XXE/XEE attacks.
     */
    public function scanFile(string $filestream): string
    {
        return $this->scan(file_get_contents($filestream));
    }
}