{"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\/nl\/blog\/administrirovanie\/reshenie-zadaniya-s-pwnable-kr-25-otp-ogranichenie-ramera-fajla-v-linux","title":{"rendered":"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/70434b41e923b3b46bcdff1ab7e03937.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\nIn dit artikel lossen we de 25e opdracht van de site op <noindex><a rel=\"nofollow\" href=\"https:\/\/pwnable.kr\/index.php\">pwnable.kr<\/a><\/noindex>.<\/p>\n<p><b class=\"spoiler_title\">Organisatie-informatie<\/b>Speciaal voor degenen die meer willen leren en zich willen ontwikkelen in verschillende gebieden van informatie- en computerbeveiliging, zal ik schrijven en vertellen over de volgende categorie\u00ebn:<\/p>\n<ul>\n<li>PWN;<\/li>\n<li>cryptografie (Crypto);<\/li>\n<li>netwerk technologie\u00ebn (Network);<\/li>\n<li>reverse engineering (Reverse Engineering);<\/li>\n<li>steganografie (Stegano);<\/li>\n<li>het zoeken naar en exploiteren van WEB-kwetsbaarheden.<\/li>\n<\/ul>\n<p>\nDaarnaast zal ik mijn ervaring delen in computerforensisch onderzoek, malware-analyse en firmware, aanvallen op draadloze netwerken en lokale netwerken, het uitvoeren van pentests en het schrijven van exploits.<br \/>\n<noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><br \/>\nOm je op de hoogte te houden van nieuwe artikelen, software en andere informatie, heb ik een <noindex><a rel=\"nofollow\" href=\"https:\/\/t.me\/RalfHackerChannel\">kanaal op Telegram<\/a><\/noindex> en <noindex><a rel=\"nofollow\" href=\"https:\/\/t.me\/RalfHackerPublicChat\">groep opgericht voor het bespreken van vragen<\/a><\/noindex> op het gebied van Informatiebeveiliging en Cyberbeveiliging. Ook zal ik persoonlijke verzoeken, vragen, voorstellen en aanbevelingen <noindex><a rel=\"nofollow\" href=\"https:\/\/t.me\/hackerralf8\">persoonlijk bekijken en iedereen beantwoorden<\/a><\/noindex>.<\/p>\n<p>Alle informatie is uitsluitend bedoeld voor educatieve doeleinden. De auteur van dit document aanvaardt geen enkele verantwoordelijkheid voor schade die aan iemand wordt toegebracht als gevolg van het gebruik van kennis en methoden die zijn verkregen door het bestuderen van dit document.<\/p>\n<h2>Oplossing van de opdracht otp<\/h2>\n<p>\nWe gaan verder met het tweede deel. Ik zal meteen zeggen dat het moeilijker is dan de eerste, maar deze keer wordt de broncode van het programma verstrekt. Vergeet de discussie hier niet (https:\/\/t.me\/RalfHackerPublicChat) en hier (https:\/\/t.me\/RalfHackerChannel). Laten we beginnen.<\/p>\n<p>Klik op het pictogram met het label otp. We krijgen een adres en poort voor de verbinding.<\/p>\n<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/fec98a1c755c36ba1a7117bfc5154611.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nWe verbinden en kijken rond op de server.<\/p>\n<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/71983f5701fe2b1366cebfb0d2d57f74.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nDe vlag die we niet kunnen lezen, het programma en de broncode ervan. Laten we de broncode bekijken.<\/p>\n<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/63e409cd939f41db29ee5c1edfa107a0.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nWe analyseren het. Het programma accepteert het wachtwoord als argument.<\/p>\n<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/5eb6bccb7ed4b82fdd01e24854c2c953.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nVervolgens worden er 16 willekeurige bytes opgeslagen in de variable otp.<\/p>\n<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/c1420a16c9721a8c87fb86277674f0f2.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nIn de map tmp wordt een bestand met een willekeurige naam (de eerste 8 bytes van otp) aangemaakt en daarin worden 8 willekeurige bytes (de laatste 8 bytes van otp) geschreven.<\/p>\n<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/d6fcc612f6cddbff338fff0aaf9b73a1.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nOm een of andere reden wordt de waarde van het aangemaakte bestand gelezen en vergeleken met het ingevoerde wachtwoord.<\/p>\n<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/42302a748b7cd57a6337be00eab2c47b.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nHier is de kwetsbaarheid. Het zit in de tussenliggende opslag van het gegenereerde getal in een bestand. We kunnen de grootte van het bestand beperken, bijvoorbeeld tot 0, zodat met het schrijven en lezen met het wachtwoord 0 zal worden vergeleken. Dit kan op de volgende manier worden gedaan.<\/p>\n<pre><code class=\"bash\"># ulimit -f 0<\/code><\/pre>\n<p>\n<img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/3af83c20d1de7435b0f40a36c8187ff0.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nLaten we nu het programma starten.<\/p>\n<p><img decoding=\"async\" alt=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/a289bd59a22aa495fe6407c3c8ff0416.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nWe krijgen een foutmelding. Geen probleem, we kunnen deze oplossen met dezelfde 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=\"Oplossing van de opdracht op pwnable.kr 25 \u2014 otp. Beperkingen van bestandsgrootte in Linux\" src=\"\/wp-content\/uploads\/2019\/10\/b8513f020879d5e5ee957e1bc137b61a.png\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\nWe krijgen de vlag en onze gemakkelijke 100 punten. En we gaan verder: in het volgende artikel bespreken we Web. U kunt zich bij ons voegen in <noindex><a rel=\"nofollow\" href=\"https:\/\/t.me\/RalfHackerChannel\">Telegram<\/a><\/noindex>.<br \/>\n<br \/>Bron: <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\/nl\/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=\"nl_NL\" \/>\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\/nl\/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\udd47Oplossing van de opdracht van pwnable.kr 25 \u2014 otp. 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