{"id":38822,"date":"2019-10-31T22:26:11","date_gmt":"2019-10-31T19:26:11","guid":{"rendered":"https:\/\/prohoster.info\/blog\/reshenie-zadaniya-s-pwnable-kr-25-otp-ogranichenie-ramera-fajla-v-linux\/"},"modified":"2019-10-31T22:26:11","modified_gmt":"2019-10-31T19:26:11","slug":"reshenie-zadaniya-s-pwnable-kr-25-otp-ogranichenie-ramera-fajla-v-linux","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pt\/blog\/administrirovanie\/reshenie-zadaniya-s-pwnable-kr-25-otp-ogranichenie-ramera-fajla-v-linux","title":{"rendered":"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/70434b41e923b3b46bcdff1ab7e03937.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\nNeste artigo, resolveremos a 25\u00aa tarefa do site <noindex><a rel=\"nofollow\" href=\"https:\/\/pwnable.kr\/index.php\">pwnable.kr<\/a><\/noindex>.<\/p>\n<p><b class=\"spoiler_title\">Informa\u00e7\u00f5es organizacionais<\/b>Especialmente para aqueles que desejam aprender algo novo e se desenvolver em qualquer \u00e1rea da seguran\u00e7a da informa\u00e7\u00e3o e da computa\u00e7\u00e3o, escrevo e compartilho sobre as seguintes categorias:<\/p>\n<ul>\n<li>PWN;<\/li>\n<li>criptografia (Crypto);<\/li>\n<li>tecnologias de rede (Network);<\/li>\n<li>engenharia reversa (Reverse Engineering);<\/li>\n<li>esteganografia (Stegano);<\/li>\n<li>pesquisa e explora\u00e7\u00e3o de vulnerabilidades WEB.<\/li>\n<\/ul>\n<p>\nAl\u00e9m disso, compartilharei minha experi\u00eancia em crimes computacionais, an\u00e1lise de malware e firmware, ataques a redes sem fio e redes locais, realiza\u00e7\u00e3o de pentests e escrita de exploits.<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><br \/>\nPara que voc\u00ea possa se manter informado sobre novos artigos, software e outras informa\u00e7\u00f5es, eu criei <noindex><a rel=\"nofollow\" href=\"https:\/\/t.me\/RalfHackerChannel\">um canal no Telegram<\/a><\/noindex> e <noindex><a rel=\"nofollow\" href=\"https:\/\/t.me\/RalfHackerPublicChat\">um grupo para discutir quaisquer quest\u00f5es<\/a><\/noindex> na \u00e1rea de seguran\u00e7a da informa\u00e7\u00e3o e gest\u00e3o de riscos. Al\u00e9m disso, suas solicita\u00e7\u00f5es pessoais, perguntas, sugest\u00f5es e recomenda\u00e7\u00f5es <noindex><a rel=\"nofollow\" href=\"https:\/\/t.me\/hackerralf8\">ser\u00e3o consideradas pessoalmente e eu responderei a todos<\/a><\/noindex>.<\/p>\n<p>Todas as informa\u00e7\u00f5es est\u00e3o apresentadas exclusivamente para fins educacionais. O autor deste documento n\u00e3o se responsabiliza por quaisquer danos causados a terceiros como resultado do uso dos conhecimentos e m\u00e9todos obtidos atrav\u00e9s do estudo deste documento.<\/p>\n<h2>Solu\u00e7\u00e3o da tarefa otp<\/h2>\n<p>\nContinuamos a segunda se\u00e7\u00e3o. Direi de antem\u00e3o que \u00e9 mais dif\u00edcil que a primeira, mas desta vez fornecem o c\u00f3digo-fonte do programa. N\u00e3o esque\u00e7amos da discuss\u00e3o aqui(https:\/\/t.me\/RalfHackerPublicChat) e aqui (https:\/\/t.me\/RalfHackerChannel). Vamos come\u00e7ar.<\/p>\n<p>Clicamos no \u00edcone com a legenda otp. Eles nos fornecem um endere\u00e7o e uma porta para conex\u00e3o.<\/p>\n<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/fec98a1c755c36ba1a7117bfc5154611.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nConectamos e exploramos o servidor.<\/p>\n<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/71983f5701fe2b1366cebfb0d2d57f74.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nA bandeira que n\u00e3o conseguimos ler, o programa e seu c\u00f3digo-fonte. Vamos ver o c\u00f3digo-fonte.<\/p>\n<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/63e409cd939f41db29ee5c1edfa107a0.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nVamos descompact\u00e1-lo. O programa aceita uma senha como argumento.<\/p>\n<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/5eb6bccb7ed4b82fdd01e24854c2c953.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nEm seguida, na vari\u00e1vel otp, s\u00e3o armazenados 16 bytes aleat\u00f3rios.<\/p>\n<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/c1420a16c9721a8c87fb86277674f0f2.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nNa pasta tmp, um arquivo com um nome aleat\u00f3rio (os primeiros 8 bytes de otp) \u00e9 criado e nele s\u00e3o gravados 8 bytes aleat\u00f3rios (os 8 bytes restantes de otp).<\/p>\n<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/d6fcc612f6cddbff338fff0aaf9b73a1.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nPor algum motivo, o valor desse arquivo criado \u00e9 lido e comparado com a senha inserida.<\/p>\n<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/42302a748b7cd57a6337be00eab2c47b.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nAqui est\u00e1 a vulnerabilidade. Ela reside na salvaguarda intermedi\u00e1ria do n\u00famero gerado em um arquivo. Podemos restringir o tamanho do arquivo, por exemplo, a 0, ent\u00e3o ao gravar e ler com a senha, ser\u00e1 comparado 0. Podemos fazer isso assim.<\/p>\n<pre><code class=\"bash\"># ulimit -f 0<\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/3af83c20d1de7435b0f40a36c8187ff0.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nAgora vamos executar o programa.<\/p>\n<p><img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/a289bd59a22aa495fe6407c3c8ff0416.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nRecebemos um erro. N\u00e3o se preocupe, pois pode ser tratado com o mesmo Python.<\/p>\n<pre><code class=\"python\">python -c \"import os, signal; signal.signal(signal.SIGXFSZ, signal.SIG_IGN); os.system('.\/otp 0')\" <\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Solu\u00e7\u00e3o da tarefa do pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o de tamanho de arquivo no Linux\" src=\"\/wp-content\/uploads\/2019\/10\/b8513f020879d5e5ee957e1bc137b61a.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nRecebemos a bandeira e nossos f\u00e1ceis 100 pontos. E seguimos: no pr\u00f3ximo artigo, abordaremos Web. Voc\u00ea pode se juntar a n\u00f3s em <noindex><a rel=\"nofollow\" href=\"https:\/\/t.me\/RalfHackerChannel\">Telegram<\/a><\/noindex>.<br \/>\n<br \/>Fonte: <a content=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/habr.com\/ru\/post\/471042\/\">habr.com<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u0412 \u0434\u0430\u043d\u043d\u043e\u0439 \u0441\u0442\u0430\u0442\u044c\u0435 \u0440\u0435\u0448\u0438\u043c 25-\u0435 \u0437\u0430\u0434\u0430\u043d\u0438\u0435 \u0441 \u0441\u0430\u0439\u0442\u0430 pwnable.kr. \u041e\u0440\u0433\u0430\u043d\u0438\u0437\u0430\u0446\u0438\u043e\u043d\u043d\u0430\u044f \u0438\u043d\u0444\u043e\u0440\u043c\u0430\u0446\u0438\u044f\u0421\u043f\u0435\u0446\u0438\u0430\u043b\u044c\u043d\u043e \u0434\u043b\u044f \u0442\u0435\u0445, \u043a\u0442\u043e \u0445\u043e\u0447\u0435\u0442 \u0443\u0437\u043d\u0430\u0432\u0430\u0442\u044c \u0447\u0442\u043e-\u0442\u043e \u043d\u043e\u0432\u043e\u0435 \u0438 \u0440\u0430\u0437\u0432\u0438\u0432\u0430\u0442\u044c\u0441\u044f \u0432 \u043b\u044e\u0431\u043e\u0439 \u0438\u0437 \u0441\u0444\u0435\u0440 \u0438\u043d\u0444\u043e\u0440\u043c\u0430\u0446\u0438\u043e\u043d\u043d\u043e\u0439 \u0438 \u043a\u043e\u043c\u043f\u044c\u044e\u0442\u0435\u0440\u043d\u043e\u0439 \u0431\u0435\u0437\u043e\u043f\u0430\u0441\u043d\u043e\u0441\u0442\u0438, \u044f \u0431\u0443\u0434\u0443 \u043f\u0438\u0441\u0430\u0442\u044c \u0438 \u0440\u0430\u0441\u0441\u043a\u0430\u0437\u044b\u0432\u0430\u0442\u044c \u043e \u0441\u043b\u0435\u0434\u0443\u044e\u0449\u0438\u0445 \u043a\u0430\u0442\u0435\u0433\u043e\u0440\u0438\u044f\u0445: PWN; \u043a\u0440\u0438\u043f\u0442\u043e\u0433\u0440\u0430\u0444\u0438\u044f (Crypto); c\u0435\u0442\u0435\u0432\u044b\u0435 \u0442\u0435\u0445\u043d\u043e\u043b\u043e\u0433\u0438\u0438 (Network); \u0440\u0435\u0432\u0435\u0440\u0441 (Reverse Engineering); \u0441\u0442\u0435\u0433\u0430\u043d\u043e\u0433\u0440\u0430\u0444\u0438\u044f (Stegano); \u043f\u043e\u0438\u0441\u043a \u0438 \u044d\u043a\u0441\u043f\u043b\u0443\u0430\u0442\u0430\u0446\u0438\u044f WEB-\u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0435\u0439. \u0412\u0434\u043e\u0431\u0430\u0432\u043e\u043a \u043a \u044d\u0442\u043e\u043c\u0443 \u044f [&hellip;]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":29120,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[688],"tags":[],"class_list":["post-38822","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-administrirovanie"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.3 - aioseo.com -->\n\t<meta name=\"robots\" content=\"max-image-preview:large\" \/>\n\t<meta name=\"author\" content=\"Yuri Gagarin\"\/>\n\t<link rel=\"canonical\" href=\"https:\/\/prohoster.info\/pt\/blog\/administrirovanie\/reshenie-zadaniya-s-pwnable-kr-25-otp-ogranichenie-ramera-fajla-v-linux\" \/>\n\t\t<meta name=\"generator\" content=\"All in One SEO (AIOSEO) 5.0.3\" \/>\n\t\t<meta property=\"og:locale\" content=\"pt_PT\" \/>\n\t\t<meta property=\"og:site_name\" content=\"ProHoster | \u041a\u0443\u043f\u0438\u0442\u044c \u043d\u0430\u0434\u0435\u0436\u043d\u044b\u0439 \u0445\u043e\u0441\u0442\u0438\u043d\u0433 \u0434\u043b\u044f \u0441\u0430\u0439\u0442\u043e\u0432 \u0441 \u0437\u0430\u0449\u0438\u0442\u043e\u0439 \u043e\u0442 DDoS, VPS VDS \u0441\u0435\u0440\u0432\u0435\u0440\u044b\" \/>\n\t\t<meta property=\"og:type\" content=\"article\" \/>\n\t\t<meta property=\"og:title\" content=\"\ud83e\udd47\u0420\u0435\u0448\u0435\u043d\u0438\u0435 \u0437\u0430\u0434\u0430\u043d\u0438\u044f \u0441 pwnable.kr 25 \u2014 otp. \u041e\u0433\u0440\u0430\u043d\u0438\u0447\u0435\u043d\u0438\u0435 \u0440\u0430\u043c\u0435\u0440\u0430 \u0444\u0430\u0439\u043b\u0430 \u0432 Linux | ProHoster\" \/>\n\t\t<meta property=\"og:url\" content=\"https:\/\/prohoster.info\/pt\/blog\/administrirovanie\/reshenie-zadaniya-s-pwnable-kr-25-otp-ogranichenie-ramera-fajla-v-linux\" \/>\n\t\t<meta property=\"og:image\" content=\"https:\/\/prohoster.info\/wp-content\/uploads\/2021\/11\/logo-350.jpg\" \/>\n\t\t<meta property=\"og:image:secure_url\" content=\"https:\/\/prohoster.info\/wp-content\/uploads\/2021\/11\/logo-350.jpg\" \/>\n\t\t<meta property=\"og:image:width\" content=\"350\" \/>\n\t\t<meta property=\"og:image:height\" content=\"350\" \/>\n\t\t<meta property=\"article:published_time\" content=\"2019-10-31T19:26:11+00:00\" \/>\n\t\t<meta property=\"article:modified_time\" content=\"2019-10-31T19:26:11+00:00\" \/>\n\t\t<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/prohoster\" \/>\n\t\t<meta property=\"article:author\" content=\"https:\/\/www.facebook.com\/prohoster\" \/>\n\t\t<!-- All in One SEO -->\n\n","aioseo_head_json":{"title":"\ud83e\udd47Solu\u00e7\u00e3o da tarefa de pwnable.kr 25 \u2014 otp. Limita\u00e7\u00e3o do tamanho do arquivo no Linux | ProHoster","description":"","canonical_url":"https:\/\/prohoster.info\/pt\/blog\/administrirovanie\/reshenie-zadaniya-s-pwnable-kr-25-otp-ogranichenie-ramera-fajla-v-linux","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":null,"og:locale":"pt_PT","og:site_name":"ProHoster | \u041a\u0443\u043f\u0438\u0442\u044c \u043d\u0430\u0434\u0435\u0436\u043d\u044b\u0439 \u0445\u043e\u0441\u0442\u0438\u043d\u0433 \u0434\u043b\u044f \u0441\u0430\u0439\u0442\u043e\u0432 \u0441 \u0437\u0430\u0449\u0438\u0442\u043e\u0439 \u043e\u0442 DDoS, VPS VDS \u0441\u0435\u0440\u0432\u0435\u0440\u044b","og:type":"article","og:title":"\ud83e\udd47\u0420\u0435\u0448\u0435\u043d\u0438\u0435 \u0437\u0430\u0434\u0430\u043d\u0438\u044f \u0441 pwnable.kr 25 \u2014 otp. \u041e\u0433\u0440\u0430\u043d\u0438\u0447\u0435\u043d\u0438\u0435 \u0440\u0430\u043c\u0435\u0440\u0430 \u0444\u0430\u0439\u043b\u0430 \u0432 Linux | ProHoster","og:url":"https:\/\/prohoster.info\/pt\/blog\/administrirovanie\/reshenie-zadaniya-s-pwnable-kr-25-otp-ogranichenie-ramera-fajla-v-linux","og:image":"https:\/\/prohoster.info\/wp-content\/uploads\/2021\/11\/logo-350.jpg","og:image:secure_url":"https:\/\/prohoster.info\/wp-content\/uploads\/2021\/11\/logo-350.jpg","og:image:width":350,"og:image:height":350,"article:published_time":"2019-10-31T19:26:11+00:00","article:modified_time":"2019-10-31T19:26:11+00:00","article:publisher":"https:\/\/www.facebook.com\/prohoster","article:author":"https:\/\/www.facebook.com\/prohoster"},"aioseo_meta_data":{"post_id":"38822","title":null,"description":null,"keywords":null,"keyphrases":null,"primary_term":null,"canonical_url":null,"og_title":null,"og_description":null,"og_object_type":"default","og_image_type":"default","og_image_url":null,"og_image_width":null,"og_image_height":null,"og_image_custom_url":null,"og_image_custom_fields":null,"og_video":null,"og_custom_url":null,"og_article_section":null,"og_article_tags":null,"twitter_use_og":false,"twitter_card":"default","twitter_image_type":"default","twitter_image_url":null,"twitter_image_custom_url":null,"twitter_image_custom_fields":null,"twitter_title":null,"twitter_description":null,"schema":{"blockGraphs":[],"customGraphs":[],"default":{"data":{"Article":[],"Course":[],"Dataset":[],"FAQPage":[],"Movie":[],"Person":[],"Product":[],"ProductReview":[],"Car":[],"Recipe":[],"Service":[],"SoftwareApplication":[],"WebPage":[]},"graphName":"","isEnabled":true},"graphs":[]},"schema_type":null,"schema_type_options":null,"pillar_content":false,"robots_default":true,"robots_noindex":false,"robots_noarchive":false,"robots_nosnippet":false,"robots_nofollow":false,"robots_noimageindex":false,"robots_noodp":false,"robots_notranslate":false,"robots_max_snippet":null,"robots_max_videopreview":null,"robots_max_imagepreview":"large","priority":null,"frequency":null,"local_seo":null,"seo_analyzer_scan_date":"2026-01-23 23:33:19","breadcrumb_settings":null,"limit_modified_date":false,"reviewed_by":null,"ai":null,"created":"2021-03-01 01:01:37","updated":"2026-01-23 23:33:19","focus_keyword":null,"additional_keywords":null,"truseo_locale":null},"gt_translate_keys":[{"key":"link","format":"url"}],"_links":{"self":[{"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/posts\/38822","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/comments?post=38822"}],"version-history":[{"count":0,"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/posts\/38822\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/media\/29120"}],"wp:attachment":[{"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/media?parent=38822"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/categories?post=38822"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/prohoster.info\/pt\/wp-json\/wp\/v2\/tags?post=38822"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}