{"id":35011,"date":"2019-10-31T22:01:50","date_gmt":"2019-10-31T19:01:50","guid":{"rendered":"https:\/\/prohoster.info\/blog\/kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root\/"},"modified":"2019-10-31T22:01:50","modified_gmt":"2019-10-31T19:01:50","slug":"kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pl\/blog\/news\/kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root","title":{"rendered":"Krytyczna luka w Exim, umo\u017cliwiaj\u0105ca wykonanie kodu na serwerze z uprawnieniami root","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Na serwerze pocztowym Exim <noindex><a rel=\"nofollow\" href=\"https:\/\/www.openwall.com\/lists\/oss-security\/2019\/06\/05\/4\">wykryto<\/a><\/noindex> krytyczny <noindex><a rel=\"nofollow\" href=\"http:\/\/www.exim.org\/static\/doc\/security\/CVE-2019-10149.txt\">luka<\/a><\/noindex> (<noindex><a rel=\"nofollow\" href=\"https:\/\/security-tracker.debian.org\/tracker\/CVE-2019-10149\">CVE-2019-10149<\/a><\/noindex>), co mo\u017ce prowadzi\u0107 do zdalnego wykonania kodu na serwerze z uprawnieniami root podczas przetwarzania specjalnie uformowanego \u017c\u0105dania. Mo\u017cliwo\u015b\u0107 wykorzystania problemu zaobserwowano w wersjach od 4.87 do 4.91 w\u0142\u0105cznie lub w przypadku kompilacji z opcj\u0105 EXPERIMENTAL_EVENT.<\/p>\n<p>W domy\u015blnej konfiguracji atak mo\u017ce by\u0107 przeprowadzony bez przeszk\u00f3d przez lokalnego u\u017cytkownika, poniewa\u017c stosowane jest ACL \u201everify = recipient\u201d, kt\u00f3re wykonuje dodatkowe kontrole dla adres\u00f3w zewn\u0119trznych. Atak zdalny jest mo\u017cliwy po zmianie ustawie\u0144, na przyk\u0142ad podczas pracy w roli drugorz\u0119dnego MX dla innej domeny, usuni\u0119cia ACL \u201everify = recipient\u201d lub dokonania okre\u015blonych zmian w local_part_suffix. Atak zdalny mo\u017ce wyst\u0105pi\u0107 r\u00f3wnie\u017c wtedy, gdy napastnik b\u0119dzie w stanie utrzyma\u0107 po\u0142\u0105czenie z serwerem otwarte przez 7 dni (na przyk\u0142ad wysy\u0142aj\u0105c po jednym bajcie na minut\u0119, aby obej\u015b\u0107 przerwanie z powodu timeoutu). Nie wyklucza to faktu, \u017ce mog\u0105 istnie\u0107 prostsze wektory ataku do zdalnego wykorzystania problemu.<\/p>\n<p>Vulnerabilno\u015b\u0107 jest spowodowana nieprawid\u0142owym sprawdzaniem adresu odbiorcy w funkcji deliver_message(), zdefiniowanej w pliku \/src\/deliver.c. Przez manipulacj\u0119 formatowaniem adresu, atakuj\u0105cy mo\u017ce osi\u0105gn\u0105\u0107 podstawienie swoich danych w argumentach komendy wywo\u0142ywanej przez funkcj\u0119 execv() z uprawnieniami root. Wykorzystanie nie wymaga stosowania skomplikowanych technik, stosowanych w przypadku przepe\u0142nie\u0144 bufora lub uszkodze\u0144 pami\u0119ci, wystarczy proste podstawienie znak\u00f3w. <\/p>\n<p>Problem zwi\u0105zany jest z u\u017cyciem konstrukcji do przekszta\u0142cania adres\u00f3w:<\/p>\n<p>         deliver_localpart = expand_string(<br \/>\n                       string_sprintf(\u201e${local_part:%s}\u201d, new-&gt;address));<br \/>\n         deliver_domain = expand_string(<br \/>\n                       string_sprintf(\u201e${domain:%s}\u201d, new-&gt;address));<\/p>\n<p>Funkcja expand_string() jest z\u0142o\u017conym mechanizmem, kt\u00f3ry rozpoznaje r\u00f3wnie\u017c komend\u0119 \u201e${run{komenda argumenty}\u201d, prowadz\u0105c\u0105 do uruchomienia zewn\u0119trznego przetwornika. W ten spos\u00f3b, aby przeprowadzi\u0107 atak w ramach sesji SMTP, lokalny u\u017cytkownik musi tylko przekaza\u0107 komend\u0119 w formacie \u2018RCPT TO \u201eusername+${run{\u2026}}@localhost\u201d, gdzie localhost jest jednym z host\u00f3w z listy local_domains, a username to nazwa istniej\u0105cego lokalnego u\u017cytkownika. <\/p>\n<p>Je\u017celi serwer dzia\u0142a jako relay pocztowy, wystarczy zdalnie wys\u0142a\u0107 komend\u0119 \u2018RCPT TO \u201e${run{\u2026}}@relaydomain.com\u201d, gdzie relaydomain.com jest jednym z host\u00f3w wymienionych w sekcji ustawie\u0144 relay_to_domains. Poniewa\u017c w exim domy\u015blnie nie stosuje si\u0119 trybu obni\u017cania uprawnie\u0144 (deliver_drop_privilege = false), komendy przekazywane przez \u201e${run{\u2026}}\u201d b\u0119d\u0105 wykonywane z uprawnieniami root.<\/p>\n<p>Warto zauwa\u017cy\u0107, \u017ce luka zosta\u0142a <noindex><a rel=\"nofollow\" href=\"https:\/\/github.com\/Exim\/exim\/commit\/7ea1237c783e380d7bdb86c90b13d8203c7ecf26\">naprawiono<\/a><\/noindex> w wydaniu 4.92 z lutego, bez zwracania uwagi na to, \u017ce poprawka mo\u017ce prowadzi\u0107 do problem\u00f3w z bezpiecze\u0144stwem. Nie ma podstaw, aby s\u0105dzi\u0107, \u017ce dosz\u0142o do \u015bwiadomego zatuszowania luki przez tw\u00f3rc\u00f3w Exim, poniewa\u017c problem zosta\u0142 rozwi\u0105zany w trakcie <noindex><a rel=\"nofollow\" href=\"https:\/\/bugs.exim.org\/show_bug.cgi?id=2310\">poprawki<\/a><\/noindex> awarii, kt\u00f3ra wyst\u0119puje podczas przesy\u0142ania niepoprawnych adres\u00f3w, a luka zosta\u0142a wykryta przez firm\u0119 Qualys podczas audytu zmian w Exim. <\/p>\n<p>Poprawka dla wcze\u015bniejszych wersji, kt\u00f3re nadal s\u0105 stosowane w dystrybucjach, jest obecnie dost\u0119pna tylko w postaci <noindex><a rel=\"nofollow\" href=\"https:\/\/git.exim.org\/exim.git\/commit\/d740d2111f189760593a303124ff6b9b1f83453d\">\u0142atki<\/a><\/noindex>. Poprawki dla wcze\u015bniejszych ga\u0142\u0119zi z rozwi\u0105zaniem problemu s\u0105 zaplanowane na 11 czerwca. Zaktualizowane pakiety s\u0105 przygotowane dla <noindex><a rel=\"nofollow\" href=\"https:\/\/security-tracker.debian.org\/tracker\/CVE-2019-10149\">Debian<\/a><\/noindex>,  <noindex><a rel=\"nofollow\" href=\"https:\/\/people.canonical.com\/~ubuntu-security\/cve\/2019\/CVE-2019-10149.html\">Ubuntu<\/a><\/noindex>, <noindex><a rel=\"nofollow\" href=\"https:\/\/bugzilla.novell.com\/show_bug.cgi?id=CVE-2019-10149\">openSUSE<\/a><\/noindex>. <noindex><a rel=\"nofollow\" href=\"https:\/\/www.archlinux.org\/packages\/community\/x86_64\/exim\/\">Arch Linux<\/a><\/noindex> i <noindex><a rel=\"nofollow\" href=\"https:\/\/bodhi.fedoraproject.org\/updates\/FEDORA-2019-7b741dcaa4\">Fedora<\/a><\/noindex> dostarczaj\u0105 wersj\u0119 4.92, w kt\u00f3rej problem nie wyst\u0119puje. RHEL i CentOS s\u0105 <noindex><a rel=\"nofollow\" href=\"https:\/\/bugzilla.redhat.com\/show_bug.cgi?id=CVE-2019-10149\">niepodatne<\/a><\/noindex>, poniewa\u017c Exim nie znajduje si\u0119 w ich standardowym repozytorium pakiet\u00f3w.<\/p>\n<p><noindex><a rel=\"nofollow\" name=\"link\"><\/a><\/noindex><\/p>\n<p>\u0179r\u00f3d\u0142o: <a \ncontent=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=50819\">opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u0412 \u043f\u043e\u0447\u0442\u043e\u0432\u043e\u043c \u0441\u0435\u0440\u0432\u0435\u0440\u0435 Exim \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u0430\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c (CVE-2019-10149), \u043a\u043e\u0442\u043e\u0440\u0430\u044f \u043c\u043e\u0436\u0435\u0442 \u043f\u0440\u0438\u0432\u0435\u0441\u0442\u0438 \u043a \u0443\u0434\u0430\u043b\u0451\u043d\u043d\u043e\u043c\u0443 \u0432\u044b\u043f\u043e\u043b\u043d\u0435\u043d\u0438\u044e \u043a\u043e\u0434\u0430 \u043d\u0430 \u0441\u0435\u0440\u0432\u0435\u0440\u0435 \u0441 \u043f\u0440\u0430\u0432\u0430\u043c\u0438 root \u043f\u0440\u0438 \u043e\u0431\u0440\u0430\u0431\u043e\u0442\u043a\u0435 \u0441\u043f\u0435\u0446\u0438\u0430\u043b\u044c\u043d\u043e \u043e\u0444\u043e\u0440\u043c\u043b\u0435\u043d\u043d\u043e\u0433\u043e \u0437\u0430\u043f\u0440\u043e\u0441\u0430. \u0412\u043e\u0437\u043c\u043e\u0436\u043d\u043e\u0441\u0442\u044c \u044d\u043a\u0441\u043f\u043b\u0443\u0430\u0442\u0430\u0446\u0438\u0438 \u043f\u0440\u043e\u0431\u043b\u0435\u043c\u044b \u043e\u0442\u043c\u0435\u0447\u0435\u043d\u0430 \u0432 \u0432\u0435\u0440\u0441\u0438\u044f\u0445 \u0441 4.87 \u043f\u043e 4.91 \u0432\u043a\u043b\u044e\u0447\u0438\u0442\u0435\u043b\u044c\u043d\u043e \u0438\u043b\u0438 \u043f\u0440\u0438 \u0441\u0431\u043e\u0440\u043a\u0435 \u0441 \u043e\u043f\u0446\u0438\u0435\u0439 EXPERIMENTAL_EVENT. \u0412 \u043a\u043e\u043d\u0444\u0438\u0433\u0443\u0440\u0430\u0446\u0438\u0438 \u043f\u043e \u0443\u043c\u043e\u043b\u0447\u0430\u043d\u0438\u044e \u0430\u0442\u0430\u043a\u0430 \u043c\u043e\u0436\u0435\u0442 \u0431\u044b\u0442\u044c \u0441\u043e\u0432\u0435\u0440\u0448\u0435\u043d\u0430 \u0431\u0435\u0437 \u043b\u0438\u0448\u043d\u0438\u0445 \u0443\u0441\u043b\u043e\u0436\u043d\u0435\u043d\u0438\u0439 \u043b\u043e\u043a\u0430\u043b\u044c\u043d\u044b\u043c \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u043c, [&hellip;]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-35011","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.1.1 - aioseo.com -->\n\t<meta name=\"description\" content=\"\u0412 \u043f\u043e\u0447\u0442\u043e\u0432\u043e\u043c \u0441\u0435\u0440\u0432\u0435\u0440\u0435 Exim \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u0430\u044f\" \/>\n\t<meta name=\"robots\" content=\"max-image-preview:large\" \/>\n\t<meta name=\"author\" content=\"Yuri Gagarin\"\/>\n\t<link rel=\"canonical\" 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