Po zisten\u00ed zranite\u013enosti na konci janu\u00e1ra, ktor\u00e1 umo\u017enila pripojenie pod pou\u017e\u00edvate\u013eom root bez overovania hesla, bolo v serveri telnetd zo s\u00faboru GNU InetUtils objaven\u00fdch nieko\u013eko sp\u00f4sobov, ako zv\u00fd\u0161i\u0165 svoje opr\u00e1vnenia, \u010do bolo d\u00f4sledkom nedostato\u010dn\u00e9ho odstr\u00e1nenia zranite\u013enosti z roku 1999 (CVE-1999-0073). <\/p>\n
Zranite\u013enosti s\u00fa sp\u00f4soben\u00e9 pr\u00edtomnos\u0165ou v telnetd, ktor\u00e1 umo\u017e\u0148uje pren\u00e1\u0161anie premenn\u00fdch prostredia klientom na server pomocou mo\u017enosti ENVIRON. Tieto premenn\u00e9 prostredia sa nastavuj\u00fa a spracov\u00e1vaj\u00fa v kontexte procesu telnetd a pren\u00e1\u0161aj\u00fa sa do n\u00edm spusten\u00fdch podriaden\u00fdch procesov, vr\u00e1tane procesu \\\/bin\\login spusten\u00e9ho s pr\u00e1vami root. Zranite\u013enos\u0165 CVE-1999-0073 umo\u017e\u0148ovala telnet klientovi prenies\u0165 premenn\u00fa prostredia LD_LIBRARY_PATH, ktorej nastavenie vedie k na\u010d\u00edtaniu \u0161peci\u00e1lne ur\u010denej zdie\u013eanej kni\u017enice pri spusten\u00ed procesu login. Pri mo\u017enosti nahr\u00e1vania s\u00faborov do syst\u00e9mu, ktor\u00fd podporuje pripojenie protokolom telnet, m\u00f4\u017ee \u00fato\u010dn\u00edk nahra\u0165 \u0161peci\u00e1lne upraven\u00fa kni\u017enicu a zabezpe\u010di\u0165 jej na\u010d\u00edtanie s pr\u00e1vami root. <\/p>\n
V telnetd z bal\u00edka GNU InetUtils bola zranite\u013enos\u0165 opraven\u00e1 z\u00e1kazom nebezpe\u010dn\u00fdch premenn\u00fdch prostredia prostredn\u00edctvom filtrovania pod\u013ea masky \u201eLD_\u201c, \u201eLIBPATH\u201c, \u201eENV\u201c, \u201eIFS\u201c a \u201e_RLD_\u201c. Av\u0161ak nezablokovanou ostala premenn\u00e1 prostredia \u201eCREDENTIALS_DIRECTORY\u201c, sprac\u00favan\u00e1 pri \u0161tarte \/usr\/bin\/login. Pomocou tejto premennej mohol pou\u017e\u00edvate\u013e zmeni\u0165 adres\u00e1r s nastaveniami poveren\u00ed a umiestni\u0165 do nov\u00e9ho adres\u00e1ra s\u00fabor login.noauth s hodnotou \u201eyes\u201c, ktor\u00fd aktivuje prihl\u00e1senie bez hesla (analogicky k odovzdaniu flagu \u201e-f\u201c procesu login). Nastavenie plat\u00ed pre v\u0161etk\u00fdch pou\u017e\u00edvate\u013eov, vr\u00e1tane root. <\/p>\n
\u00datok spo\u010d\u00edva v vytvoren\u00ed nepovolen\u00e9ho podadres\u00e1ra v svojom dom\u00e1com adres\u00e1ri, nahrat\u00ed s\u00faboru login.noauth do neho a pokuse o prihl\u00e1senie so nastaven\u00edm premennej prostredia \u201eCREDENTIALS_DIRECTORY=u\u017e vytvoren\u00fd adres\u00e1r\u201c a prenosom premennej prostredia \u201eUSER=root\u201c (v telnet existuje re\u017eim automatick\u00e9ho pripojenia, kde sa meno pou\u017e\u00edvate\u013ea nez\u00edska z pr\u00edkazov\u00e9ho riadku, ale pren\u00e1\u0161a cez premenn\u00fa prostredia USER). Pr\u00edklad exploit. <\/p>\n
N\u00e1sledne bol odhalen\u00fd \u010fal\u0161\u00ed sp\u00f4sob, ako z\u00edska\u0165 root pr\u00edstup cez telnetd, ktor\u00fd s\u00favis\u00ed s manipul\u00e1ciou s premenn\u00fdmi prostredia OUTPUT_CHARSET a LANGUAGE, spracov\u00e1van\u00fdmi kni\u017enicou GNU gettext, ako aj s premennou prostredia GCONV_PATH pou\u017e\u00edvanou v glibc. Nastaven\u00edm premenn\u00fdch prostredia OUTPUT_CHARSET a LANGUAGE m\u00f4\u017ee \u00fato\u010dn\u00edk aktivova\u0165 v gettext funkcionalitu konvertovania k\u00f3dovania znakov, ktor\u00e1 vol\u00e1 funkciu iconv_open(). Pri vykonan\u00ed funkcie iconv_open() pri na\u010d\u00edtan\u00ed konfigura\u010dn\u00e9ho s\u00faboru gconv-modules sa cesta vypo\u010d\u00edtava na z\u00e1klade premennej prostredia GCONV_PATH. Pomocou subsit\u00facie s\u00faboru gconv-modules je mo\u017en\u00e9 zabezpe\u010di\u0165 na\u010d\u00edtanie vlastnej zdie\u013eanej kni\u017enice po\u010das v\u00fdstupu lokalizovanej re\u0165azca procesom login. <\/p>\n
CVE identifik\u00e1tory pre uveden\u00e9 zranite\u013enosti zatia\u013e neboli priraden\u00e9. Ako met\u00f3da ochrany sa zva\u017euje vyu\u017eitie bieleho zoznamu povolen\u00fdch hodn\u00f4t (\u201eTERM\u201c, \u201eDISPLAY\u201c, \u201eUSER\u201c, \u201eLOGNAME\u201c a \u201ePOSIXLY_CORRECT\u201c) s blokovan\u00edm v\u0161etk\u00fdch ostatn\u00fdch premenn\u00fdch prostredia, podobne ako to funguje s premenn\u00fdmi prostredia v OpenSSH. Zranite\u013enosti boli potvrden\u00e9 v bal\u00edku GNU InetUtils, implement\u00e1cia servera<\/a> telnetd, ktor\u00fd sa dod\u00e1va v Debian, Ubuntu a odvozen\u00fdch distrib\u00faci\u00e1ch. Opravy pre GNU InetUtils zatia\u013e nie s\u00fa k dispoz\u00edcii. V Rocky Linux 9 sa dod\u00e1va modifikovan\u00fd telnetd, ktor\u00fd nie je zranite\u013en\u00fd a namiesto filtrovania nebezpe\u010dn\u00fdch premenn\u00fdch prostredia obsahuje kontrolu pod\u013ea bieleho zoznamu. Filtrovanie pod\u013ea bieleho zoznamu je tie\u017e implementovan\u00e9 v telnetd vo FreeBSD. V OpenBSD bol telnetd z syst\u00e9mu vyl\u00fa\u010den\u00fd u\u017e v roku 2005. \u0421\u043b\u0435\u0434\u043e\u043c \u0437\u0430 \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043d\u043e\u0439 \u0432 \u043a\u043e\u043d\u0446\u0435 \u044f\u043d\u0432\u0430\u0440\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c\u044e, \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u0432\u0448\u0435\u0439 \u043f\u043e\u0434\u043a\u043b\u044e\u0447\u0438\u0442\u044c\u0441\u044f \u043f\u043e\u0434 \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u043c root \u0431\u0435\u0437 \u043f\u0440\u043e\u0432\u0435\u0440\u043a\u0438 \u043f\u0430\u0440\u043e\u043b\u044f, \u0432 \u0441\u0435\u0440\u0432\u0435\u0440\u0435 telnetd \u0438\u0437 \u043d\u0430\u0431\u043e\u0440\u0430 GNU InetUtils \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043e \u043d\u0435\u0441\u043a\u043e\u043b\u044c\u043a\u043e \u0441\u043f\u043e\u0441\u043e\u0431\u043e\u0432 \u043f\u043e\u0432\u044b\u0448\u0435\u043d\u0438\u044f \u0441\u0432\u043e\u0438\u0445 \u043f\u0440\u0438\u0432\u0438\u043b\u0435\u0433\u0438\u0439, \u0441\u0442\u0430\u0432\u0448\u0438\u0445 \u0441\u043b\u0435\u0434\u0441\u0442\u0432\u0438\u0435\u043c \u043d\u0435\u043f\u043e\u043b\u043d\u043e\u0433\u043e \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u0438\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 \u0432 1999 \u0433\u043e\u0434\u0443 (CVE-1999-0073). \u0423\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 \u0432\u044b\u0437\u0432\u0430\u043d\u044b \u043d\u0430\u043b\u0438\u0447\u0438\u0435\u043c \u0432 telnetd \u0432\u043e\u0437\u043c\u043e\u0436\u043d\u043e\u0441\u0442\u0438 \u043f\u0435\u0440\u0435\u0434\u0430\u0447\u0438 \u043a\u043b\u0438\u0435\u043d\u0442\u043e\u043c \u043f\u0435\u0440\u0435\u043c\u0435\u043d\u043d\u044b\u0445 \u043e\u043a\u0440\u0443\u0436\u0435\u043d\u0438\u044f \u043d\u0430 \u0441\u0435\u0440\u0432\u0435\u0440 \u043f\u0440\u0438 \u043f\u043e\u043c\u043e\u0449\u0438 \u043e\u043f\u0446\u0438\u0438 ENVIRON. \u041f\u043e\u0434\u043e\u0431\u043d\u044b\u0435 \u043f\u0435\u0440\u0435\u043c\u0435\u043d\u043d\u044b\u0435 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":8,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-162791","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\udd47S\u00e9ria nov\u00fdch zranite\u013enost\u00ed v telnetd, ktor\u00e9 umo\u017e\u0148uj\u00fa z\u00edska\u0165 root opr\u00e1vnenia v syst\u00e9me | ProHoster","description":"N\u00e1sledne po zisten\u00ed zranite\u013enosti na konci janu\u00e1ra, ktor\u00e1 umo\u017e\u0148ovala pripoji\u0165 sa ako pou\u017e\u00edvate\u013e root bez kontroly hesla, sa v serveri telnetd z bal\u00edka GNU InetUtils odhalilo nieko\u013eko sp\u00f4sobov, ako zv\u00fd\u0161i\u0165 svoje opr\u00e1vnenia.","canonical_url":"https:\/\/prohoster.info\/sk\/blog\/news\/seriya-novyh-uyazvimostej-v-telnetd-pozvolyayushhih-poluchit-root-privilegii-v-sisteme","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":null,"og:locale":"sk_SK","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\u0421\u0435\u0440\u0438\u044f \u043d\u043e\u0432\u044b\u0445 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Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"