Po zji\u0161t\u011bn\u00e9 zranitelnosti na konci ledna, kter\u00e1 umo\u017e\u0148ovala p\u0159ihl\u00e1\u0161en\u00ed pod u\u017eivatelsk\u00fdm jm\u00e9nem root bez kontroly hesla, byly na serveru telnetd z bal\u00edku GNU InetUtils odhaleny dal\u0161\u00ed zp\u016fsoby zv\u00fd\u0161en\u00ed privilegi\u00ed, kter\u00e9 byly d\u016fsledkem nedostate\u010dn\u00e9ho vy\u0159e\u0161en\u00ed zranitelnosti z roku 1999 (CVE-1999-0073). <\/p>\n
Zranitelnosti jsou zp\u016fsobeny t\u00edm, \u017ee telnetd umo\u017e\u0148uje klientovi p\u0159en\u00e1\u0161et prom\u011bnn\u00e9 prost\u0159ed\u00ed na server pomoc\u00ed volby ENVIRON. Tyto prom\u011bnn\u00e9 prost\u0159ed\u00ed jsou nastaveny a zpracov\u00e1v\u00e1ny v kontextu procesu telnetd a p\u0159ed\u00e1vaj\u00ed se do j\u00edm spu\u0161t\u011bn\u00fdch podproces\u016f, v\u010detn\u011b procesu \/bin\/login spu\u0161t\u011bn\u00e9ho s pr\u00e1vy root. Zranitelnost CVE-1999-0073 umo\u017enila telnet klientovi p\u0159edat prom\u011bnnou prost\u0159ed\u00ed LD_LIBRARY_PATH, jej\u00ed\u017e nastaven\u00ed zp\u016fsobuje na\u010dten\u00ed u\u017eivatelsky zadan\u00e9 sd\u00edlen\u00e9 knihovny p\u0159i spu\u0161t\u011bn\u00ed procesu login. P\u0159i mo\u017enosti nahr\u00e1v\u00e1n\u00ed soubor\u016f do syst\u00e9mu podporuj\u00edc\u00edho p\u0159ipojen\u00ed p\u0159es protokol telnet m\u016f\u017ee \u00fato\u010dn\u00edk nahr\u00e1t speci\u00e1ln\u011b vytvo\u0159enou knihovnu a zajistit jej\u00ed na\u010dten\u00ed s pr\u00e1vy root. <\/p>\n
V telnetd z bal\u00ed\u010dku GNU InetUtils byla zranitelnost odstran\u011bna zak\u00e1z\u00e1n\u00edm nebezpe\u010dn\u00fdch prom\u011bnn\u00fdch prost\u0159ed\u00ed pomoc\u00ed filtrace podle masek \u201eLD_\u201c, \u201eLIBPATH\u201c, \u201eENV\u201c, \u201eIFS\u201c a \u201e_RLD_\u201c. Zat\u00edmco prom\u011bnn\u00e1 prost\u0159ed\u00ed \u201eCREDENTIALS_DIRECTORY\u201c, zpracov\u00e1van\u00e1 p\u0159i spu\u0161t\u011bn\u00ed \/usr\/bin\/login, z\u016fstala nezablokovan\u00e1. D\u00edky t\u00e9to prom\u011bnn\u00e9 mohl u\u017eivatel zm\u011bnit adres\u00e1\u0159 s nastaven\u00edm p\u0159ihla\u0161ovac\u00edch \u00fadaj\u016f a um\u00edstit do nov\u00e9ho adres\u00e1\u0159e soubor login.noauth s hodnotou \u201eyes\u201c, co\u017e aktivovalo p\u0159ihl\u00e1\u0161en\u00ed bez hesla (podobn\u011b jako p\u0159ed\u00e1n\u00ed p\u0159\u00edznaku \u201e-f\u201c procesu login). Nastaven\u00ed plat\u00ed pro v\u0161echny u\u017eivatele, v\u010detn\u011b root. <\/p>\n
\u00datok spo\u010d\u00edv\u00e1 ve vytvo\u0159en\u00ed nep\u0159ihla\u0161ovan\u00e9ho podadres\u00e1\u0159e ve sv\u00e9m dom\u00e1c\u00edm adres\u00e1\u0159i, nahr\u00e1n\u00ed do n\u011bj souboru login.noauth a pokusem o p\u0159ihl\u00e1\u0161en\u00ed s nastaven\u00edm prom\u011bnn\u00e9 prost\u0159ed\u00ed \u201eCREDENTIALS_DIRECTORY=vytvo\u0159en\u00fd adres\u00e1\u0159\u201c a p\u0159ed\u00e1n\u00edm prom\u011bnn\u00e9 prost\u0159ed\u00ed \u201eUSER=root\u201c (v telnetu je k dispozici re\u017eim automatick\u00e9ho p\u0159ipojen\u00ed, ve kter\u00e9m je u\u017eivatelsk\u00e9 jm\u00e9no p\u0159evzato nikoli z p\u0159\u00edkazov\u00e9ho \u0159\u00e1dku, ale p\u0159ed\u00e1no prost\u0159ednictv\u00edm prom\u011bnn\u00e9 prost\u0159ed\u00ed USER). P\u0159\u00edklad exploitu. <\/p>\n
N\u00e1sledn\u011b byl identifikov\u00e1n dal\u0161\u00ed zp\u016fsob, jak z\u00edskat root p\u0159\u00edstup p\u0159es telnetd, kter\u00fd souvis\u00ed s manipulac\u00ed s prom\u011bnn\u00fdmi prost\u0159ed\u00ed OUTPUT_CHARSET a LANGUAGE zpracov\u00e1van\u00fdmi knihovnou GNU gettext, a prom\u011bnnou prost\u0159ed\u00ed GCONV_PATH pou\u017e\u00edvanou v glibc. Nastaven\u00edm prom\u011bnn\u00fdch prost\u0159ed\u00ed OUTPUT_CHARSET a LANGUAGE m\u016f\u017ee \u00fato\u010dn\u00edk aktivovat v gettext funk\u010dnost p\u0159evodu znakov\u00fdch sad, kter\u00e1 vyvol\u00e1v\u00e1 funkci iconv_open(). P\u0159i prov\u00e1d\u011bn\u00ed funkce iconv_open() p\u0159i na\u010d\u00edt\u00e1n\u00ed konfigura\u010dn\u00edho souboru gconv-modules se cesta vypo\u010d\u00edt\u00e1v\u00e1 s ohledem na prom\u011bnnou prost\u0159ed\u00ed GCONV_PATH. Pomoc\u00ed podstr\u010den\u00ed souboru gconv-modules lze organizovat na\u010d\u00edt\u00e1n\u00ed vlastn\u00ed sd\u00edlen\u00e9 knihovny b\u011bhem v\u00fdstupu lokalizovan\u00e9ho \u0159et\u011bzce procesem login. <\/p>\n
CVE identifik\u00e1tory pro uveden\u00e9 zranitelnosti dosud nebyly p\u0159id\u011bleny. Jako metodu ochrany se zva\u017euje pou\u017eit\u00ed b\u00edl\u00e9ho seznamu povolen\u00fdch hodnot (\u201eTERM\u201c, \u201eDISPLAY\u201c, \u201eUSER\u201c, \u201eLOGNAME\u201c a \u201ePOSIXLY_CORRECT\u201c) s blokov\u00e1n\u00edm v\u0161ech ostatn\u00edch prom\u011bnn\u00fdch prost\u0159ed\u00ed, podobn\u011b jako se pracuje s prom\u011bnn\u00fdmi prost\u0159ed\u00ed v OpenSSH. Zranitelnosti byly potvrzeny v bal\u00ed\u010dku GNU InetUtils, implementace. serveru<\/a> telnetd, kter\u00e1 se dod\u00e1v\u00e1 v Debianu, Ubuntu a derivovan\u00fdch distribuc\u00edch. Opravy pro GNU InetUtils zat\u00edm nejsou k dispozici. V Rocky Linux 9 je dod\u00e1v\u00e1n modifikovan\u00fd telnetd, kter\u00fd nen\u00ed zraniteln\u00fd, a m\u00edsto filtrov\u00e1n\u00ed nebezpe\u010dn\u00fdch prom\u011bnn\u00fdch prost\u0159ed\u00ed implementuje kontrolu podle whitelistu. Filtrov\u00e1n\u00ed podle whitelistu je tak\u00e9 implementov\u00e1no v telnetd ve FreeBSD. V OpenBSD byl telnetd ze syst\u00e9mu odstran\u011bn v roce 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\udd47 S\u00e9rie nov\u00fdch zranitelnost\u00ed v telnetd, kter\u00e9 umo\u017e\u0148uj\u00ed z\u00edskat root opr\u00e1vn\u011bn\u00ed v syst\u00e9mu | ProHoster","description":"N\u00e1sledn\u011b po zranitelnosti z konce ledna, kter\u00e1 umo\u017e\u0148ovala p\u0159ipojen\u00ed 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Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"