{"id":37876,"date":"2019-10-31T22:20:17","date_gmt":"2019-10-31T19:20:17","guid":{"rendered":"https:\/\/prohoster.info\/blog\/raskryty-podrobnosti-kriticheskoj-uyazvimosti-v-exim\/"},"modified":"2019-10-31T22:20:17","modified_gmt":"2019-10-31T19:20:17","slug":"raskryty-podrobnosti-kriticheskoj-uyazvimosti-v-exim","status":"publish","type":"post","link":"https:\/\/prohoster.info\/hu\/blog\/news\/raskryty-podrobnosti-kriticheskoj-uyazvimosti-v-exim","title":{"rendered":"A kritikus sebezhet\u0151s\u00e9g r\u00e9szletei felfedve az Exim-ben","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Megjelent<\/a><\/noindex> jav\u00edt\u00f3 kiad\u00e1s Exim 4.92.2<\/a><\/noindex> kritikai hiba kijav\u00edt\u00e1sa sebezhet\u0151s\u00e9gek<\/a><\/noindex> (CVE-2019-15846<\/a><\/noindex>), amely az alap\u00e9rtelmezett konfigur\u00e1ci\u00f3ban t\u00e1voli k\u00f3dfuttat\u00e1shoz vezethet, ha a t\u00e1mad\u00f3 root jogosults\u00e1gokkal rendelkezik. A probl\u00e9ma csak TLS t\u00e1mogat\u00e1sa eset\u00e9n jelentkezik, \u00e9s egy speci\u00e1lisan kialak\u00edtott kliens tan\u00fas\u00edtv\u00e1ny vagy a SNI m\u00f3dos\u00edtott \u00e9rt\u00e9ke \u00e1tk\u00fcld\u00e9s\u00e9vel kihaszn\u00e1lhat\u00f3. A s\u00e9r\u00fcl\u00e9kenys\u00e9g identified<\/a><\/noindex> a Qualys c\u00e9g \u00e1ltal.<\/p>\n

Probl\u00e9ma m\u00e1r 2016 \u00f3ta jelen van (lehet, hogy a probl\u00e9ma kihaszn\u00e1l\u00e1s\u00e1nak felt\u00e9telei csak egyes m\u00e1s nemr\u00e9giben t\u00f6rt\u00e9nt v\u00e1ltoz\u00e1sok ut\u00e1n jelentkeztek).<\/a><\/noindex> a speci\u00e1lis karakterek v\u00e9delm\u00e9t v\u00e9gz\u0151 kezel\u0151ben (string_interpret_escape()<\/a><\/noindex> A string.c) \u00e9s az a t\u00e9ny, hogy a karakter ‘\’ a sor v\u00e9g\u00e9n a null\u00e1s karakter el\u0151tt \u00e9rtelmez\u0151dik (‘\0’), \u00e9s elrejti azt. Az elrejt\u00e9s sor\u00e1n az ‘\’ \u00e9s az azt k\u00f6vet\u0151 null\u00e1s k\u00f3dot a sor v\u00e9g\u00e9n egyetlen karakterk\u00e9nt kezelik, \u00e9s a mutat\u00f3 a sor m\u00f6g\u00f6tti adatokra helyez\u0151dik \u00e1t, amelyeket a sor folytat\u00e1sak\u00e9nt dolgoznak fel. <\/p>\n

A string_interpret_escape() h\u00edv\u00e1s\u00e1t gener\u00e1l\u00f3 k\u00f3d a t\u00e9nyleges m\u00e9ret alapj\u00e1n foglal pufferhelyet, \u00e9s a be\u00e1ll\u00edtott mutat\u00f3 a puffer hat\u00e1rain k\u00edv\u00fclre ker\u00fcl. Ennek megfelel\u0151en, amikor a bemeneti sor feldolgoz\u00e1s\u00e1ra ker\u00fcl sor, a megadott ter\u00fcletr\u0151l t\u00f6rt\u00e9nik az adatolvas\u00e1s, m\u00edg a dek\u00f3dolt sorra \u00edr\u00e1s k\u00eds\u00e9rlete pufferhat\u00e1ron k\u00edv\u00fcli \u00edr\u00e1st eredm\u00e9nyezhet.<\/p>\n

Alap\u00e9rtelmezett konfigur\u00e1ci\u00f3ban a s\u00e9r\u00fcl\u00e9kenys\u00e9g a SNI-n kereszt\u00fcl t\u00f6rt\u00e9n\u0151 kifejezetten kialak\u00edtott adatok \u00e1tk\u00fcld\u00e9s\u00e9vel kihaszn\u00e1lhat\u00f3, amikor v\u00e9dett kapcsolatot l\u00e9tes\u00edt\u00fcnk a szerverhez. A probl\u00e9ma szint\u00e9n kihaszn\u00e1lhat\u00f3 a peerdn \u00e9rt\u00e9kek m\u00f3dos\u00edt\u00e1s\u00e1val olyan konfigur\u00e1ci\u00f3k eset\u00e9n, amelyeket kliens tan\u00fas\u00edtv\u00e1ny alap\u00fa hiteles\u00edt\u00e9sre \u00e1ll\u00edtottak be, vagy tan\u00fas\u00edtv\u00e1nyok import\u00e1l\u00e1sakor. A SNI-n \u00e9s a peerdn-en kereszt\u00fcli t\u00e1mad\u00e1sok az Exim 4.80 megjelen\u00e9s\u00e9t\u0151l kezd\u0151d\u0151en lehets\u00e9gesek. Exim 4.80<\/a><\/noindex>, ahol a string_unprinting() funkci\u00f3t alkalmazt\u00e1k a peerdn \u00e9s SNI tartalm\u00e1nak dek\u00f3dol\u00e1s\u00e1ra.<\/p>\n

SNI t\u00e1mad\u00e1shoz egy exploit protot\u00edpus k\u00e9sz\u00fclt, amely az i386 \u00e9s amd64 architekt\u00far\u00e1kon fut Linux rendszereken Glibc-vel. Az exploit adatfel\u00fcletet alkalmaz a t\u00e1rhelyen, ami a mem\u00f3ria fel\u00fcl\u00edr\u00e1s\u00e1hoz vezet, ahol a napl\u00f3f\u00e1jl neve t\u00e1rol\u00f3dik. A f\u00e1jl neve «\\\/..\\\/..\\\/..\\\/..\\\/..\\\/..\\\/..\\\/..\\\/etc\\\/passwd»-ra cser\u00e9l\u0151dik. Ezt k\u00f6vet\u0151en fel\u00fcl\u00edr\u00f3dik a k\u00fcld\u0151 c\u00edm\u00e9t tartalmaz\u00f3 v\u00e1ltoz\u00f3, amely els\u0151k\u00e9nt ker\u00fcl a napl\u00f3z\u00e1sra, lehet\u0151v\u00e9 t\u00e9ve egy \u00faj felhaszn\u00e1l\u00f3 hozz\u00e1ad\u00e1s\u00e1t a rendszerhez. <\/p>\n

A s\u00e9r\u00fcl\u00e9kenys\u00e9get jav\u00edt\u00f3 csomagfriss\u00edt\u00e9sek a disztrib\u00faci\u00f3k \u00e1ltal kiad\u00e1sra ker\u00fcltek Debian<\/a><\/noindex>, Ubuntu<\/a><\/noindex>, Fedora<\/a><\/noindex>, SUSE\/openSUSE<\/a><\/noindex> \u00e9s FreeBSD<\/a><\/noindex>. A RHEL \u00e9s a CentOS nem \u00e9rintett a probl\u00e9m\u00e1ban, mivel az Exim nem szerepel a hivatalos csomagrep\u00f3j\u00e1ban (sz\u00fcks\u00e9g eset\u00e9n az<\/a><\/noindex>, mivel az Exim nem r\u00e9sze a hivatalos csomagok t\u00e1rol\u00f3j\u00e1nak (a EPEL<\/a><\/noindex> friss\u00edt\u00e9s m\u00e1r<\/a><\/noindex> form\u00e1lva<\/a><\/noindex>, de m\u00e9g nem ker\u00fclt be.<\/a><\/noindex> a nyilv\u00e1nos t\u00e1rol\u00f3ba). Az Exim k\u00f3dban a probl\u00e9ma egy sorra cs\u00f6kkentett k\u00f3ddal orvosolhat\u00f3 patch<\/a><\/noindex>, amely letiltja a visszafejt\u0151 visszafel\u00e9 per jel hat\u00e1s\u00e1t, ha az a sor v\u00e9g\u00e9n tal\u00e1lhat\u00f3.<\/p>\n

Az TLS t\u00e1mogat\u00e1s letilt\u00e1s\u00e1val, vagy a k\u00f6vetkez\u0151, az ACL szakaszba val\u00f3 hozz\u00e1ad\u00e1s\u00e1val megker\u00fclheti a sebezhet\u0151s\u00e9get:
\naz ACL «acl_smtp_mail» szekci\u00f3:\n<\/p>\n

elutas\u00edt felt\u00e9tel = ${if eq{\\}{${substr{-1}{1}{$tls_in_sni}}}}
\n elutas\u00edt felt\u00e9tel = ${if eq{\\}{${substr{-1}{1}{$tls_in_peerdn}}}}<\/p>\n

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

Forr\u00e1s: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u041e\u043f\u0443\u0431\u043b\u0438\u043a\u043e\u0432\u0430\u043d \u043a\u043e\u0440\u0440\u0435\u043a\u0442\u0438\u0440\u0443\u044e\u0449\u0438\u0439 \u0432\u044b\u043f\u0443\u0441\u043a Exim 4.92.2 \u0441 \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u0438\u0435\u043c \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u043e\u0439 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 (CVE-2019-15846), \u043a\u043e\u0442\u043e\u0440\u0430\u044f \u0432 \u043a\u043e\u043d\u0444\u0438\u0433\u0443\u0440\u0430\u0446\u0438\u0438 \u043f\u043e \u0443\u043c\u043e\u043b\u0447\u0430\u043d\u0438\u044e \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 \u0437\u043b\u043e\u0443\u043c\u044b\u0448\u043b\u0435\u043d\u043d\u0438\u043a\u0430 \u0441 \u043f\u0440\u0430\u0432\u0430\u043c\u0438 root. 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\u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u043a\u043e\u043c\u043f\u0430\u043d\u0438\u0435\u0439 Qualys. \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u043f\u0440\u0438\u0441\u0443\u0442\u0441\u0442\u0432\u0443\u0435\u0442 \u0432 \u043e\u0431\u0440\u0430\u0431\u043e\u0442\u0447\u0438\u043a\u0435 \u044d\u043a\u0440\u0430\u043d\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u044f \u0441\u043f\u0435\u0446\u0441\u0438\u043c\u0432\u043e\u043b\u043e\u0432 […]<\/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-37876","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\udd47R\u00e9szletek a kritikus Exim sebezhet\u0151s\u00e9gr\u0151l | ProHoster","description":"Megjelent a jav\u00edt\u00f3kiad\u00e1s az Eximhez.","canonical_url":"https:\/\/prohoster.info\/hu\/blog\/news\/raskryty-podrobnosti-kriticheskoj-uyazvimosti-v-exim","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":null,"og:locale":"hu_HU","og:site_name":"ProHoster | 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