{"id":39289,"date":"2019-10-31T22:29:21","date_gmt":"2019-10-31T19:29:21","guid":{"rendered":"https:\/\/prohoster.info\/blog\/ataka-cpdos-pozvolyayushhaya-sdelat-nedostupnymi-stranitsy-otdavaemye-cherez-cdn\/"},"modified":"2019-10-31T22:29:21","modified_gmt":"2019-10-31T19:29:21","slug":"ataka-cpdos-pozvolyayushhaya-sdelat-nedostupnymi-stranitsy-otdavaemye-cherez-cdn","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/news\/ataka-cpdos-pozvolyayushhaya-sdelat-nedostupnymi-stranitsy-otdavaemye-cherez-cdn","title":{"rendered":"CPDoS attack, which allows making pages delivered through CDN unavailable.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Researchers from the University of Hamburg and the University of Cologne<br \/>\n<noindex><a rel=\"nofollow\" href=\"https:\/\/cpdos.org\/\">developed<\/a><\/noindex> new attack techniques on content delivery networks and caching proxies \u2014 <noindex><a rel=\"nofollow\" href=\"https:\/\/cpdos.org\/paper\/Your_Cache_Has_Fallen__Cache_Poisoned_Denial_of_Service_Attack__Preprint_.pdf\">CPDoS<\/a><\/noindex> (Cache-Poisoned Denial-of-Service). This attack allows for denial of access to a page through cache poisoning. <\/p>\n<p>The problem is related to the fact that CDNs cache not only successfully executed requests but also situations where the HTTP server returns an error. Typically, when there are issues with request formation, the server issues an error 400 (Bad Request), with the exception of IIS, which issues a 404 (Not Found) error for overly large headers. The standard allows caching only for errors with codes 404 (Not Found), 405 (Method Not Allowed), 410 (Gone), and 501 (Not Implemented), but some CDNs also cache responses with code 400 (Bad Request), which depends on the sent request. <\/p>\n<p>Attackers can trigger a \"400 Bad Request\" error on the original resource by sending a request with specifically formatted HTTP headers. These headers are not considered by the CDN, so the cached information will reflect the inability to access the page, and all other valid user requests until the timeout may result in an error, even though the original site serves content without any issues. <\/p>\n<p>Three attack variants have been proposed to force the HTTP server to return an error:  <\/p>\n<ul>\n<li class=\"l\"> HMO (HTTP Method Override) \u2014 an attacker can override the original request method via the headers \"X-HTTP-Method-Override\", \"X-HTTP-Method\", or \"X-Method-Override\", which are supported by some servers but not taken into account by the CDN. For example, it is possible to change the original method \"GET\" to a prohibited method \"DELETE\" on the server or an inapplicable method for static content \"POST\";\n<p><center><noindex><a rel=\"nofollow\" href=\"https:\/\/cpdos.org\/img\/HMO.png\"><img decoding=\"async\" alt=\"CPDoS attack, which allows making pages delivered through CDN unavailable.\" src=\"\/wp-content\/uploads\/2019\/10\/6449e613e38cfb3cb1f2f185921214e9.jpeg\" style=\"display:block;margin: 0 auto;\" \/><\/a><\/noindex><\/center><\/p>\n<li class=\"l\"> HHO (HTTP Header Oversize) \u2014 an attacker can configure the header size such that it exceeds the limit of the origin server but does not fall under the CDN's restrictions. For instance, Apache httpd limits header size to 8 KB, while the Amazon CloudFront CDN allows headers of up to 20 KB;<br \/>\n<center><noindex><a rel=\"nofollow\" href=\"https:\/\/cpdos.org\/img\/HHO.png\"><img decoding=\"async\" alt=\"CPDoS attack, which allows making pages delivered through CDN unavailable.\" src=\"\/wp-content\/uploads\/2019\/10\/2bbefaff1f9b5b1b4e568801cd7ac7cd.jpeg\" style=\"display:block;margin: 0 auto;\" \/><\/a><\/noindex><\/center><\/p>\n<li class=\"l\"> HMC (HTTP Meta Character) \u2014 an attacker can include special characters in the request (\\n, \\r, \\a) that are deemed invalid on the origin server but are ignored in the CDN.\n<p><center><noindex><a rel=\"nofollow\" href=\"https:\/\/cpdos.org\/img\/HMC.png\"><img decoding=\"async\" alt=\"CPDoS attack, which allows making pages delivered through CDN unavailable.\" src=\"\/wp-content\/uploads\/2019\/10\/5e8426e93a48735796b600db00a5c99d.jpeg\" style=\"display:block;margin: 0 auto;\" \/><\/a><\/noindex><\/center><\/p>\n<\/ul>\n<p>The most affected by the attack was the CDN CloudFront used in Amazon Web Services (AWS). Currently, Amazon has already resolved the issue by disabling error caching, but it took researchers over three months to get the protection implemented. The issue also impacted Cloudflare, Varnish, Akamai, CDN77, and<br \/>\nFastly, but the attack through them was limited to targeted servers using IIS, ASP.NET, <noindex><a rel=\"nofollow\" href=\"https:\/\/github.com\/pallets\/flask\">Flask<\/a><\/noindex> and <noindex><a rel=\"nofollow\" href=\"https:\/\/github.com\/playframework\/play1\/issues\/1300\">Play 1<\/a><\/noindex>. <noindex><a rel=\"nofollow\" href=\"https:\/\/cpdos.org\/paper\/Your_Cache_Has_Fallen__Cache_Poisoned_Denial_of_Service_Attack__Preprint_.pdf\">It is noted<\/a><\/noindex>, which means that potentially 11% of domains belonging to the U.S. Department of Defense, 16% of URLs from the HTTP Archive database, and about 30% of the top 500 sites in the Alexa ranking could be vulnerable to the attack.<\/p>\n<p>As a workaround to block attacks on the site side, one can use the header \"Cache-Control: no-store\", which prohibits response caching. In some CDNs, for example, in<br \/>\n CloudFront and Akamai, you can disable error caching at the profile settings level. Firewalls for web applications (WAF, Web Application Firewall) can also be used for protection, but they must be implemented on the CDN side before the caching hosts.<\/p>\n<p><noindex><a rel=\"nofollow\" name=\"link\"><\/a><\/noindex><\/p>\n<p>Source: <a \ncontent=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=51753\">opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u0418\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u0438 \u0438\u0437 \u0413\u0430\u043c\u0431\u0443\u0440\u0433\u0441\u043a\u043e\u0433\u043e \u0438 \u041a\u0451\u043b\u044c\u043d\u0441\u043a\u043e\u0433\u043e \u0443\u043d\u0438\u0432\u0435\u0440\u0441\u0438\u0442\u0435\u0442\u043e\u0432 \u0440\u0430\u0437\u0440\u0430\u0431\u043e\u0442\u0430\u043b\u0438 \u043d\u043e\u0432\u0443\u044e \u0442\u0435\u0445\u043d\u0438\u043a\u0443 \u0430\u0442\u0430\u043a \u043d\u0430 \u0441\u0435\u0442\u0438 \u0434\u043e\u0441\u0442\u0430\u0432\u043a\u0438 \u043a\u043e\u043d\u0442\u0435\u043d\u0442\u0430 \u0438 \u043a\u044d\u0448\u0438\u0440\u0443\u044e\u0449\u0438\u0435 \u043f\u0440\u043e\u043a\u0441\u0438 &#8212; CPDoS (Cache-Poisoned Denial-of-Service). \u0410\u0442\u0430\u043a\u0430 \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u0435\u0442 \u0434\u043e\u0431\u0438\u0442\u044c\u0441\u044f \u043e\u0442\u043a\u0430\u0437\u0430 \u0434\u043e\u0441\u0442\u0443\u043f\u0430 \u043a \u0441\u0442\u0440\u0430\u043d\u0438\u0446\u0435 \u0447\u0435\u0440\u0435\u0437 \u043e\u0442\u0440\u0430\u0432\u043b\u0435\u043d\u0438\u0435 \u043a\u044d\u0448\u0430. \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u0441\u0432\u044f\u0437\u0430\u043d\u0430 \u0441 \u0442\u0435\u043c, \u0447\u0442\u043e CDN \u043a\u044d\u0448\u0438\u0440\u0443\u044e\u0442 \u043d\u0435 \u0442\u043e\u043b\u044c\u043a\u043e \u0443\u0441\u043f\u0435\u0448\u043d\u043e \u0432\u044b\u043f\u043e\u043b\u043d\u0435\u043d\u043d\u044b\u0435 \u0437\u0430\u043f\u0440\u043e\u0441\u044b, \u043d\u043e \u0438 \u0441\u0438\u0442\u0443\u0430\u0446\u0438\u0438, \u043a\u043e\u0433\u0434\u0430 http-\u0441\u0435\u0440\u0432\u0435\u0440 \u0432\u043e\u0437\u0432\u0440\u0430\u0449\u0430\u0435\u0442 \u043e\u0448\u0438\u0431\u043a\u0443. \u041a\u0430\u043a \u043f\u0440\u0430\u0432\u0438\u043b\u043e, \u043f\u0440\u0438 \u043f\u0440\u043e\u0431\u043b\u0435\u043c\u0430\u0445 \u0441 [&hellip;]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":39290,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-39289","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.2 - aioseo.com -->\n\t<meta name=\"description\" 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