{"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\/hr\/blog\/news\/kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root","title":{"rendered":"Kriti\u010dna ranjivost u Eximu koja omogu\u0107uje izvr\u0161avanje koda na serveru s root pravima","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Na po\u0161tanskom serveru Exim otkrivena je<\/a><\/noindex> kriti\u010dna ranljivost<\/a><\/noindex> (CVE-2019-10149<\/a><\/noindex>), \u0161to mo\u017ee dovesti do udaljenog izvr\u0161avanja koda na serveru s root pravima prilikom obrade posebno oblikovanog zahtjeva. Mogu\u0107nost iskori\u0161tavanja problema zabilje\u017eena je u verzijama od 4.87 do 4.91 uklju\u010duju\u0107i ili prilikom gradnje s opcijom EXPERIMENTAL_EVENT.<\/p>\n

U zadanoj konfiguraciji napad mo\u017ee biti izvr\u0161en bez dodatnih komplikacija od strane lokalnog korisnika, jer je primenjen ACL \u201everify = recipient\u201c, koji vr\u0161i dodatne provere za spoljne adrese. Izvo\u0111enje daljinskog napada mogu\u0107e je menjaju\u0107i postavke, na primer, kada funkcioni\u0161e kao sekundarni MX za drugi domen, uklanjaju\u0107i ACL \u201everify = recipient\u201c ili odre\u0111ene izmene u local_part_suffix. Daljinski napad je tako\u0111e mogu\u0107 ako napada\u010d mo\u017ee odr\u017eati vezu sa serverom otvorenom tokom 7 dana (na primer, \u0161alju\u0107i po jedan bajt u minutu kako bi izbegao prekid zbog vremena). Pri tome se ne isklju\u010duje da postoje i jednostavniji vektori napada za daljinsku eksploataciju problema.<\/p>\n

Ranljivost je uzrokovana neispravnom provjerom adrese primatelja u funkciji deliver_message(), definiranoj u datoteci \/src\/deliver.c. Kroz manipulaciju s formatiranjem adrese, napada\u010d mo\u017ee posti\u0107i umetanje svojih podataka u argumente komande koja se poziva preko funkcije execv() s root pravima. Za iskori\u0161tavanje nije potrebno primjenjivanje slo\u017eenih tehnika kori\u0161tenih prilikom preljevanja bafera ili o\u0161te\u0107enja memorije, dovoljno je samo jednostavno umetanje simbola. <\/p>\n

Problem je povezan s primjenom konstrukcije za pretvorbu adresa:<\/p>\n

deliver_localpart = expand_string(
\n string_sprintf(\"${local_part:%s}\", new->address));
\n deliver_domain = expand_string(
\n string_sprintf(\"${domain:%s}\", new->address));<\/p>\n

Funkcija expand_string() je prekompleksna kombinacija, koja izme\u0111u ostalog prepoznaje komandu \"${run{komanda argumenti}\", \u0161to dovodi do pokretanja spoljnog procesora. Tako da, za napad unutar SMTP sesije, lokalnom korisniku je dovoljno da prenese komandu poput \u2018RCPT TO \u201eusername+${run{...}}@localhost\u201c\u2019, gde je localhost jedan od hostova iz liste local_domains, a username je ime postoje\u0107eg lokalnog korisnika. <\/p>\n

Ako server funkcioni\u0161e kao po\u0161tanski rel\u00e9, dovoljno je udaljeno poslati komandu \u2018RCPT TO \u201e${run{...}}@relaydomain.com\u201c\u2019, gde je relaydomain.com jedan od hostova navedenih u sekciji postavki relay_to_domains. Po\u0161to po defaultu u exim-u nije aktiviran re\u017eim smanjenja privilegija (deliver_drop_privilege = false), komande prosledjene kroz \u201e${run{...}}\u201c bi\u0107e izvr\u0161ene sa root privilegijama.<\/p>\n

Zanimljivo je da je ranjivost otkrivena rije\u0161ena<\/a><\/noindex> u izdanju 4.92 iz velja\u010de bez nagla\u0161avanja da bi ispravak mogao dovesti do problema s sigurno\u0161\u0107u. Nema razloga vjerovati da su developeri Exima svjesno prikrivali ranjivost, jer je problem rije\u0161en tijekom ispravke<\/a><\/noindex> gre\u0161ke koja se dogodila prilikom prijenosa neispravnih adresa, a ranjivost je otkrila tvrtka Qualys tijekom revizije promjena u Eximu. <\/p>\n

Ispravak za pro\u0161le verzije koje se i dalje koriste u distribucijama trenutno je dostupan samo u obliku zakrpe<\/a><\/noindex>. Korektivna izdanja za prethodne grane s ispravkom problema planirana su za 11. lipnja. A\u017euriranja paketa pripremljena su za Debian<\/a><\/noindex>, Ubuntu<\/a><\/noindex>, openSUSE<\/a><\/noindex>. Arch Linux<\/a><\/noindex> i Fedora<\/a><\/noindex> dostavljaju verziju 4.92, u kojoj problem nije prisutan. RHEL i CentOS nisu pogo\u0111eni tim problemom,<\/a><\/noindex>budu\u0107i da Exim nije uklju\u010den u njihov slu\u017ebeni repozitorij paketa.<\/p>\n

<\/a><\/noindex><\/p>\n

Izvor: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\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. 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\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u043c, […]<\/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\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Kriti\u010dna ranjivost u Eximu omogu\u0107ava izvo\u0111enje koda na serveru s pravima root | ProHoster","description":"Na po\u0161tanskom serveru Exim otkrivena je 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