{"id":71318,"date":"2020-02-25T07:34:19","date_gmt":"2020-02-25T04:34:19","guid":{"rendered":"https:\/\/prohoster.info\/blog\/uyazvimosti-v-opensmtpd-pozvolyayushhie-udalyonno-i-lokalno-poluchit-prava-root"},"modified":"2020-03-03T16:10:53","modified_gmt":"2020-03-03T13:10:53","slug":"uyazvimosti-v-opensmtpd-pozvolyayushhie-udalyonno-i-lokalno-poluchit-prava-root","status":"publish","type":"post","link":"https:\/\/prohoster.info\/hu\/blog\/news\/uyazvimosti-v-opensmtpd-pozvolyayushhie-udalyonno-i-lokalno-poluchit-prava-root","title":{"rendered":"Az OpenSMTPD s\u00e9r\u00fcl\u00e9kenys\u00e9gei, amelyek t\u00e1volr\u00f3l \u00e9s helyben root jogosults\u00e1gokhoz juttathatnak","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Qualys c\u00e9g felt\u00e1rta<\/a><\/noindex> m\u00e9g egy t\u00e1voli kritikus sebezhet\u0151s\u00e9get (CVE-2020-8794) tal\u00e1ltak a levelez\u0151 szerveren OpenSMTPD<\/a><\/noindex>, amelyet az OpenBSD projekt fejleszt. Mint ami janu\u00e1r v\u00e9g\u00e9n ker\u00fclt napvil\u00e1gra vulnerability<\/a><\/noindex>, az \u00faj hiba lehet\u0151v\u00e9 teszi a t\u00e1voli, tetsz\u0151leges shell parancsok v\u00e9grehajt\u00e1s\u00e1t a szerveren root felhaszn\u00e1l\u00f3i jogokkal. A sebezhet\u0151s\u00e9g eliminates<\/a><\/noindex> a kiad\u00e1sban OpenSMTPD 6.6.4p1<\/a><\/noindex>. <\/p>\n

A probl\u00e9ma a lev\u00e9l t\u00e1voli levelez\u0151 szerverre t\u00f6rt\u00e9n\u0151 k\u00e9zbes\u00edt\u00e9s\u00e9t v\u00e9gz\u0151 k\u00f3d hib\u00e1j\u00e1b\u00f3l fakad (nem a bej\u00f6v\u0151 kapcsolatok kezel\u00e9s\u00e9t v\u00e9gz\u0151 k\u00f3db\u00f3l). A t\u00e1mad\u00e1s lehet\u0151s\u00e9ge fenn\u00e1ll a kliens \u00e9s a szerver oldal\u00e1n is. A kliens oldal\u00e1n a t\u00e1mad\u00e1s a szok\u00e1sos OpenSMTPD konfigur\u00e1ci\u00f3ban lehets\u00e9ges, amelyben az OpenSMTPD csak a bels\u0151 h\u00e1l\u00f3zati interf\u00e9szen (localhost) fogadja a k\u00e9r\u00e9seket, \u00e9s lev\u00e9l\u00fczeneteket k\u00fcld k\u00fcls\u0151 szerverekre. A sebezhet\u0151s\u00e9g kihaszn\u00e1l\u00e1s\u00e1hoz elegend\u0151, hogy a lev\u00e9l k\u00e9zbes\u00edt\u00e9se sor\u00e1n az OpenSMTPD kapcsolatba l\u00e9pjen egy t\u00e1mad\u00f3 \u00e1ltal ir\u00e1ny\u00edtott levelez\u0151 szerverrel, vagy hogy a t\u00e1mad\u00f3 bele tudjon avatkozni a kliens kapcsolat\u00e1ba (MITM vagy \u00e1tir\u00e1ny\u00edt\u00e1s DNS vagy BGP t\u00e1mad\u00e1sok k\u00f6zben).<\/p>\n

A szerver oldal\u00e1n t\u00f6rt\u00e9n\u0151 t\u00e1mad\u00e1shoz az OpenSMTPD-nak be kell \u00e1ll\u00edtva lennie olyan k\u00fcls\u0151 h\u00e1l\u00f3zati k\u00e9r\u00e9sek fogad\u00e1s\u00e1ra m\u00e1s levelez\u0151 szerverekt\u0151l, vagy k\u00fcls\u0151 szolg\u00e1ltat\u00e1sokat kell \u00fczemeltetnie, amelyek lehet\u0151v\u00e9 teszik, hogy tetsz\u0151leges e-mail c\u00edmre k\u00fcldjenek k\u00e9r\u00e9seket (p\u00e9ld\u00e1ul c\u00edmmeger\u0151s\u00edt\u0151 \u0171rlapokat webhelyeken). P\u00e9ld\u00e1ul a t\u00e1mad\u00f3 csatlakozhat az OpenSMTPD szerverhez, \u00e9s k\u00fcldhet egy hib\u00e1s levelet (nem l\u00e9tez\u0151 felhaszn\u00e1l\u00f3nak), amely az elk\u00fcld\u00f6tt lev\u00e9l hibak\u00f3dj\u00e1val (bounce) t\u00e9r vissza a t\u00e1mad\u00f3 szerver\u00e9re. A t\u00e1mad\u00f3 kihaszn\u00e1lhatja a sebezhet\u0151s\u00e9get, amikor az OpenSMTPD \u00e9rtes\u00edt\u00e9st k\u00fcld a t\u00e1mad\u00f3 szerver\u00e9re. A t\u00e1mad\u00e1s sor\u00e1n bejuttatott shell parancsokat egy f\u00e1jlba helyezik, amely root jogokkal fut le, amikor az OpenSMTPD \u00fajraindul, ez\u00e9rt a t\u00e1mad\u00f3nak meg kell v\u00e1rnia az OpenSMTPD \u00fajraind\u00edt\u00e1s\u00e1t, vagy sz\u00e1nd\u00e9kosan \u00f6ssze kell t\u00f6rnie az OpenSMTPD-t.<\/p>\n

A probl\u00e9ma a mta_io() funkci\u00f3ban tal\u00e1lhat\u00f3, amely a t\u00e1voli szerver \u00e1ltal visszaadott t\u00f6bbsoros v\u00e1lasz elemz\u00e9s\u00e9re szolg\u00e1l\u00f3 k\u00f3dra vonatkozik, miut\u00e1n a kapcsolat l\u00e9trej\u00f6tt (p\u00e9ld\u00e1ul \u201e250-ENHANCEDSTATUSCODES\u201d \u00e9s \u201e250 HELP\u201d). Az OpenSMTPD-n\u00e9l azt v\u00e1rj\u00e1k, hogy az els\u0151 sor egy h\u00e1romjegy\u0171 sz\u00e1mot \u00e9s sz\u00f6veget tartalmaz, amelyet a \u201e-\u201d karakter v\u00e1laszt el, m\u00edg a m\u00e1sodik sorban egy h\u00e1romjegy\u0171 sz\u00e1m \u00e9s sz\u00f6veg szerepel, amelyet sz\u00f3k\u00f6z v\u00e1laszt el. Ha a m\u00e1sodik sorban a h\u00e1romjegy\u0171 sz\u00e1m ut\u00e1n nem k\u00f6vetkezik sz\u00f3k\u00f6z \u00e9s sz\u00f6veg, akkor a sz\u00f6veg meghat\u00e1roz\u00e1s\u00e1ra haszn\u00e1lt mutat\u00f3 a \u201e\u201d karaktert k\u00f6vet\u0151 b\u00e1jtra \u00e1ll\u00edt\u00f3dik, \u00e9s megk\u00eds\u00e9relj\u00fck a vonal v\u00e9ge ut\u00e1n k\u00f6vetkez\u0151 adatokat a pufferbe m\u00e1solni.<\/p>\n

Az OpenBSD projekt k\u00e9r\u00e9s\u00e9re a sebezhet\u0151s\u00e9g kihaszn\u00e1l\u00e1s\u00e1nak r\u00e9szleteit 2023. febru\u00e1r 26-ig k\u00e9sleltett\u00e9k a felhaszn\u00e1l\u00f3k rendszereik friss\u00edt\u00e9s\u00e9nek lehet\u0151s\u00e9g\u00e9\u00e9rt. A probl\u00e9ma a k\u00f3dalapban 2015 december \u00f3ta jelen van, de a root jogosults\u00e1gokkal t\u00f6rt\u00e9n\u0151 k\u00f3dfuttat\u00e1s kihaszn\u00e1l\u00e1sa 2018 m\u00e1jus \u00f3ta lehets\u00e9ges. A kutat\u00f3k egy m\u0171k\u00f6d\u0151 kihaszn\u00e1l\u00e1si protot\u00edpust k\u00e9sz\u00edtettek, amely sikeresen tesztelve lett az OpenSMTPD OpenBSD 6.6, OpenBSD 5.9, Debian 10, Debian 11 (tesztel\u00e9s) \u00e9s Fedora 31 verzi\u00f3iban. <\/p>\n

Az OpenSMTPD-ben is identified<\/a><\/noindex> van egy m\u00e1sik sebezhet\u0151s\u00e9g (CVE-2020-8793), amely lehet\u0151v\u00e9 teszi a helyi felhaszn\u00e1l\u00f3 sz\u00e1m\u00e1ra, hogy elolvassa b\u00e1rmely f\u00e1jl els\u0151 sor\u00e1t a rendszeren. P\u00e9ld\u00e1ul elolvashat\u00f3 az els\u0151 sor az \/etc\/master.passwd f\u00e1jlban, amelyben a root felhaszn\u00e1l\u00f3 jelszav\u00e1nak hash-e tal\u00e1lhat\u00f3. A sebezhet\u0151s\u00e9g lehet\u0151v\u00e9 teszi a m\u00e1s felhaszn\u00e1l\u00f3 \u00e1ltal birtokolt f\u00e1jl teljes tartalm\u00e1nak elolvas\u00e1s\u00e1t is, ha az a \/var\/spool\/smtpd\/ k\u00f6nyvt\u00e1rral egy f\u00e1jlrendszerben tal\u00e1lhat\u00f3. A probl\u00e9ma sok Linux disztrib\u00faci\u00f3ban nem kihaszn\u00e1lhat\u00f3, ahol a \/proc\/sys\/fs\/protected_hardlinks \u00e9rt\u00e9ke 1. <\/p>\n

A probl\u00e9ma az probl\u00e9m\u00e1kra<\/a><\/noindex>, amelyeket a Qualys 2015-\u00f6s auditja sor\u00e1n eml\u00edtettek. A t\u00e1mad\u00f3 el\u00e9rheti, hogy a k\u00f3dja a \u201e_smtpq\u201d csoport jogainak birtok\u00e1ban fusson azzal, hogy a \u201ePATH=.\u201d v\u00e1ltoz\u00f3t be\u00e1ll\u00edtja, \u00e9s a jelenlegi k\u00f6nyvt\u00e1rban elhelyez egy makemap nev\u0171 szkriptet (az smtpctl seg\u00e9dprogram a makemap-ot explicit \u00fatvonal megad\u00e1sa n\u00e9lk\u00fcl ind\u00edtja el). Miut\u00e1n hozz\u00e1f\u00e9r\u00e9st kapott a \u201e_smtpq\u201d csoporthoz, a t\u00e1mad\u00f3 versenyhelyzetet id\u00e9zhet el\u0151 (nagy f\u00e1jlt hozhat l\u00e9tre az offline k\u00f6nyvt\u00e1rban \u00e9s SIGSTOP jelet k\u00fcldhet), \u00e9s a feldolgoz\u00e1s befejez\u00e9se el\u0151tt a f\u00e1jlt kicser\u00e9lheti az offline k\u00f6nyvt\u00e1rban egy kem\u00e9ny szimbolikus linkre, amely a c\u00e9lf\u00e1jlra mutat, amelynek tartalm\u00e1t el akarja olvasni.<\/p>\n

\u00c9rdekes, hogy a Fedora 31-ben a sebezhet\u0151s\u00e9g lehet\u0151v\u00e9 teszi a root csoport privil\u00e9giumainak azonnali megad\u00e1s\u00e1t, mivel a smtpctl folyamat setgid root z\u00e1szl\u00f3val van ell\u00e1tva, nem pedig setgid smtpq-val. A root csoporthoz val\u00f3 hozz\u00e1f\u00e9r\u00e9ssel \u00e1t lehet \u00edrni a \/var\/lib\/sss\/mc\/passwd tartalm\u00e1t, \u00e9s teljes root hozz\u00e1f\u00e9r\u00e9st lehet szerezni a rendszerben.<\/p>\n

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

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

\u041a\u043e\u043c\u043f\u0430\u043d\u0438\u044f Qualys \u0432\u044b\u044f\u0432\u0438\u043b\u0430 \u0435\u0449\u0451 \u043e\u0434\u043d\u0443 \u0443\u0434\u0430\u043b\u0451\u043d\u043d\u0443\u044e \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u0443\u044e \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c (CVE-2020-8794) \u0432 \u043f\u043e\u0447\u0442\u043e\u0432\u043e\u043c \u0441\u0435\u0440\u0432\u0435\u0440\u0435 OpenSMTPD, \u0440\u0430\u0437\u0432\u0438\u0432\u0430\u0435\u043c\u043e\u043c \u043f\u0440\u043e\u0435\u043a\u0442\u043e\u043c OpenBSD. \u041a\u0430\u043a \u0438 \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043d\u0430\u044f \u0432 \u043a\u043e\u043d\u0446\u0435 \u044f\u043d\u0432\u0430\u0440\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c, \u043d\u043e\u0432\u0430\u044f \u043f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u0434\u0430\u0451\u0442 \u0432\u043e\u0437\u043c\u043e\u0436\u043d\u043e\u0441\u0442\u044c \u0443\u0434\u0430\u043b\u0451\u043d\u043d\u043e \u0432\u044b\u043f\u043e\u043b\u043d\u0438\u0442\u044c \u043f\u0440\u043e\u0438\u0437\u0432\u043e\u043b\u044c\u043d\u044b\u0435 \u043a\u043e\u043c\u0430\u043d\u0434\u044b shell \u043d\u0430 \u0441\u0435\u0440\u0432\u0435\u0440\u0435 \u0441 \u043f\u0440\u0430\u0432\u0430\u043c\u0438 \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u044f root. \u0423\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u0430 \u0432 \u0432\u044b\u043f\u0443\u0441\u043a\u0435 OpenSMTPD 6.6.4p1. \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u0432\u044b\u0437\u0432\u0430\u043d\u0430 \u043e\u0448\u0438\u0431\u043a\u043e\u0439 \u0432 \u043a\u043e\u0434\u0435, \u043e\u0441\u0443\u0449\u0435\u0441\u0442\u0432\u043b\u044f\u044e\u0449\u0435\u043c \u0434\u043e\u0441\u0442\u0430\u0432\u043a\u0443 \u043f\u043e\u0447\u0442\u044b \u043d\u0430 \u0443\u0434\u0430\u043b\u0451\u043d\u043d\u044b\u0439 \u043f\u043e\u0447\u0442\u043e\u0432\u044b\u0439 […]<\/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-71318","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\udd47Sebezhet\u0151s\u00e9gek az OpenSMTPD-ben, amelyek lehet\u0151v\u00e9 teszik a root jogok t\u00e1voli \u00e9s helyi megszerz\u00e9s\u00e9t | ProHoster","description":"A Qualys c\u00e9g felfedezett egy \u00faj t\u00e1voli kritikus sebezhet\u0151s\u00e9get (CVE-2020-8794) a 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