{"id":93917,"date":"2020-09-11T01:41:59","date_gmt":"2020-09-10T23:41:59","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimost-v-tls-dopuskayushhaya-opredelenie-klyucha-dlya-soedinenij-na-baze-shifrov-dh"},"modified":"2020-09-11T01:41:59","modified_gmt":"2020-09-10T23:41:59","slug":"uyazvimost-v-tls-dopuskayushhaya-opredelenie-klyucha-dlya-soedinenij-na-baze-shifrov-dh","status":"publish","type":"post","link":"https:\/\/prohoster.info\/hu\/blog\/news\/uyazvimost-v-tls-dopuskayushhaya-opredelenie-klyucha-dlya-soedinenij-na-baze-shifrov-dh","title":{"rendered":"TLS sebezhet\u0151s\u00e9g, amely lehet\u0151v\u00e9 teszi a DH titkos\u00edt\u00e1ssal rendelkez\u0151 kapcsolatok kulcs\u00e1nak meghat\u00e1roz\u00e1s\u00e1t","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Kib\u0151v\u00fclt<\/a><\/noindex> inform\u00e1ci\u00f3k az \u00fajr\u00f3l sebezhet\u0151s\u00e9gek<\/a><\/noindex> (CVE-2020-1968) a TLS protokollban, amely a Raccoon k\u00f3dnevet kapta
\nRaccoon<\/a><\/noindex> \u00e9s lehet\u0151v\u00e9 teszi, hogy ritka k\u00f6r\u00fclm\u00e9nyek k\u00f6z\u00f6tt meghat\u00e1rozzuk a pre-master titkos kulcsot, amelyet a TLS kapcsolatok, bele\u00e9rtve a HTTPS-t, dek\u00f3dol\u00e1s\u00e1hoz haszn\u00e1lhatunk, a tranzitforgalom elfog\u00e1sa (MITM) sor\u00e1n. Megjegyzend\u0151, hogy a t\u00e1mad\u00e1s v\u00e9grehajt\u00e1sa rendk\u00edv\u00fcl neh\u00e9z \u00e9s ink\u00e1bb elm\u00e9leti jelleg\u0171. A t\u00e1mad\u00e1shoz specifikus TLS-szerver konfigur\u00e1ci\u00f3 \u00e9s a m\u0171veletek feldolgoz\u00e1si idej\u00e9nek rendk\u00edv\u00fcl pontos m\u00e9r\u00e9se sz\u00fcks\u00e9ges.<\/p>\n

A probl\u00e9ma k\u00f6zvetlen\u00fcl a TLS specifik\u00e1ci\u00f3j\u00e1ban rejlik, \u00e9s csak azokat a kapcsolatokat \u00e9rinti, amelyek a DH (Diffie-Hellman, TLS_DH_*») alap\u00fa titkos\u00edt\u00e1sokat haszn\u00e1lj\u00e1k. Az ECDH titkos\u00edt\u00e1ssal nem tapasztalhat\u00f3 probl\u00e9ma, \u00e9s azok biztons\u00e1gban maradnak. Csak az 1.2-es vagy ann\u00e1l kor\u00e1bbi TLS protokollok sebezhet\u0151k, az 1.3-as TLS protokoll nem \u00e9rintett. A sebezhet\u0151s\u00e9g megjelenik azokn\u00e1l a TLS implement\u00e1ci\u00f3kn\u00e1l, amelyek \u00fajra felhaszn\u00e1lj\u00e1k a DH titkos kulcsot k\u00fcl\u00f6nb\u00f6z\u0151 TLS kapcsolatokban (ez a viselked\u00e9s k\u00f6r\u00fclbel\u00fcl az Alexa Top 1M szerverek 4,4%-\u00e1n\u00e1l fordul el\u0151).<\/p>\n

Az OpenSSL 1.0.2e \u00e9s kor\u00e1bbi verzi\u00f3kban a DH alapkulcs \u00fajrahaszn\u00e1l\u00f3dik az \u00f6sszes szerverkapcsolatban, kiv\u00e9ve ha kifejezetten nincs be\u00e1ll\u00edtva az SSL_OP_SINGLE_DH_USE opci\u00f3. Az OpenSSL 1.0.2f-t\u0151l kezdve a DH alapkulcs \u00fajrahaszn\u00e1l\u00f3dik csak akkor, ha statikus DH titkos\u00edt\u00e1st haszn\u00e1lnak («DH-*», p\u00e9ld\u00e1ul «DH-RSA-AES256-SHA»). Az OpenSSL 1.1.1-ben a sebezhet\u0151s\u00e9g nem jelentkezik, mivel ebben az \u00e1gon nem haszn\u00e1lj\u00e1k a DH alapkulcsot, \u00e9s statikus DH titkos\u00edt\u00f3k sem alkalmaznak. <\/p>\n

A DH kulcsmegoszt\u00e1si m\u00f3dszer haszn\u00e1latakor a kapcsolat mindk\u00e9t oldala v\u00e9letlenszer\u0171 priv\u00e1t kulcsokat gener\u00e1l (ezek a kulcsok «a» \u00e9s «b»), amelyek alapj\u00e1n kisz\u00e1m\u00edtj\u00e1k \u00e9s elk\u00fcldik a nyilv\u00e1nos kulcsokat (ga mod p \u00e9s gb mod p). Miut\u00e1n mindk\u00e9t f\u00e9l megkapta a nyilv\u00e1nos kulcsokat, k\u00f6z\u00f6sen kisz\u00e1m\u00edtj\u00e1k a k\u00f6z\u00f6s alapkulcsot (gab mod p), amely a session kulcsok l\u00e9trehoz\u00e1s\u00e1hoz sz\u00fcks\u00e9ges. A Raccoon t\u00e1mad\u00e1s lehet\u0151v\u00e9 teszi az alapkulcs meghat\u00e1roz\u00e1s\u00e1t a harmadik f\u00e9lt\u0151l sz\u00e1rmaz\u00f3 inform\u00e1ci\u00f3k elemz\u00e9s\u00e9n kereszt\u00fcl, tekintettel arra, hogy a TLS 1.2-es verzi\u00f3j\u00e1ig a specifik\u00e1ci\u00f3k el\u0151\u00edrj\u00e1k az alapkulcs kezdeti nulla byte-jainak elvet\u00e9s\u00e9t, miel\u0151tt azokkal sz\u00e1moln\u00e1nk.<\/p>\n

A cs\u00f6kkentett els\u0151dleges kulcsot a k\u00fcl\u00f6nb\u00f6z\u0151 adatok feldolgoz\u00e1sakor tapasztalt k\u00e9sleked\u00e9sekre \u00e9p\u00fcl\u0151, szekvenci\u00e1lis kulcsgener\u00e1l\u00f3 funkci\u00f3hoz adj\u00e1k \u00e1t. Az id\u0151z\u00edt\u00e9sek pontos m\u00e9r\u00e9se lehet\u0151v\u00e9 teszi a t\u00e1mad\u00f3 sz\u00e1m\u00e1ra, hogy nyomokat (oracle) szerezzen, amelyek alapj\u00e1n meg\u00e1llap\u00edthatja, hogy az els\u0151dleges kulcs null\u00e1val kezd\u0151dik-e vagy sem. P\u00e9ld\u00e1ul a t\u00e1mad\u00f3 elfoghatja a kliens \u00e1ltal k\u00fcld\u00f6tt nyilv\u00e1nos kulcsot (ga), visszak\u00fcldheti a szerverre \u00e9s meg\u00e1llap\u00edthatja
\nhogy a kapott els\u0151dleges kulcs null\u00e1val kezd\u0151dik-e.<\/p>\n

Az alapkulcs egy byte-j\u00e1nak meghat\u00e1roz\u00e1sa \u00f6nmag\u00e1ban semmit sem \u00e9r, de ha a t\u00e1mad\u00f3 elfogja a kliens \u00e1ltal a kapcsolat egyeztet\u00e9sekor \u00e1tadott «ga» \u00e9rt\u00e9ket, form\u00e1lhat egy m\u00e1sik \u00e9rt\u00e9kekb\u0151l \u00e1ll\u00f3 halmazt, amely a «ga» \u00e9rt\u00e9kkel van kapcsolatban, \u00e9s ezeket k\u00fcl\u00f6nb\u00f6z\u0151 kapcsolat egyeztet\u00e9si szakaszok sor\u00e1n elk\u00fcldheti a szerverre. Az «gri*ga» \u00e9rt\u00e9kek elk\u00e9sz\u00edt\u00e9s\u00e9vel \u00e9s elk\u00fcld\u00e9s\u00e9vel a t\u00e1mad\u00f3 az elt\u00e9r\u00e9si k\u00e9s\u00e9s elemz\u00e9s\u00e9vel meghat\u00e1rozhatja azokat az \u00e9rt\u00e9keket, amelyek a null\u00e1val kezd\u0151d\u0151 alapkulcsokhoz vezetnek. Ha siker\u00fcl az ilyen \u00e9rt\u00e9keket meghat\u00e1roznia, a t\u00e1mad\u00f3 egy egyenletrendszert alkothat. megold\u00e1s\u00e1hoz<\/a><\/noindex> a rejtett sz\u00e1mok probl\u00e9m\u00e1ja<\/a><\/noindex> \u00e9s kisz\u00e1molhatja az eredeti els\u0151dleges kulcsot. <\/p>\n

\"TLS<\/center><\/p>\n

Az OpenSSL-ben l\u00e9v\u0151 sebezhet\u0151s\u00e9gek kapott<\/a><\/noindex> alacsony vesz\u00e9lyszint, a jav\u00edt\u00e1s pedig a probl\u00e9m\u00e1s \"TLS_DH_*\" titkos\u00edt\u00f3k \u00e1thelyez\u00e9s\u00e9re korl\u00e1toz\u00f3dott az alap\u00e9rtelmezett m\u00f3don letiltott, el\u00e9gtelen v\u00e9detts\u00e9g\u0171 titkos\u00edt\u00f3k kateg\u00f3ri\u00e1j\u00e1ba (\"weak-ssl-ciphers\"). Hasonl\u00f3k\u00e9ppen j\u00e1rtak el a Mozilla fejleszt\u0151i is, akik letiltott\u00e1k<\/a><\/noindex> a Firefoxban haszn\u00e1lt NSS k\u00f6nyvt\u00e1rban a DH \u00e9s DHE titkos\u00edt\u00e1si halmazokkal. A Firefox 78-t\u00f3l kezd\u0151d\u0151en a probl\u00e9m\u00e1s titkos\u00edt\u00f3k le vannak tiltva. A Chrome t\u00e1mogat\u00e1sa a DH-val m\u00e1r 2016-ban megsz\u0171nt. A BearSSL, BoringSSL, Botan, Mbed TLS \u00e9s s2n k\u00f6nyvt\u00e1rak nem \u00e9rintettek a probl\u00e9m\u00e1ban, mivel nem t\u00e1mogatj\u00e1k a DH titkos\u00edt\u00f3kat vagy a DH statikus v\u00e1ltozatait. <\/p>\n

K\u00fcl\u00f6n kiemelend\u0151k az egy\u00e9b probl\u00e9m\u00e1k (CVE-2020-5929<\/a><\/noindex>) az F5 BIG-IP eszk\u00f6z\u00f6k TLS-stackj\u00e9ben, amelyek re\u00e1lisabb\u00e1 teszik a t\u00e1mad\u00e1st. Konkr\u00e9tan felfedt\u00e9k az eszk\u00f6z\u00f6k viselked\u00e9sbeli elt\u00e9r\u00e9seit, amikor az els\u0151dleges kulcs elej\u00e9n nulla b\u00e1jt tal\u00e1lhat\u00f3, amelyet pontos k\u00e9sleked\u00e9sm\u00e9r\u00e9s helyett fel lehet haszn\u00e1lni.<\/p>\n

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

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

\u0420\u0430\u0441\u043a\u0440\u044b\u0442\u044b \u0441\u0432\u0435\u0434\u0435\u043d\u0438\u044f \u043e \u043d\u043e\u0432\u043e\u0439 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 (CVE-2020-1968) \u0432 \u043f\u0440\u043e\u0442\u043e\u043a\u043e\u043b\u0435 TLS, \u043f\u043e\u043b\u0443\u0447\u0438\u0432\u0448\u0435\u0439 \u043a\u043e\u0434\u043e\u0432\u043e\u0435 \u0438\u043c\u044f Raccoon \u0438 \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0435\u0439 \u043f\u0440\u0438 \u0440\u0435\u0434\u043a\u043e\u043c \u0441\u0442\u0435\u0447\u0435\u043d\u0438\u0438 \u043e\u0431\u0441\u0442\u043e\u044f\u0442\u0435\u043b\u044c\u0441\u0442\u0432 \u043e\u043f\u0440\u0435\u0434\u0435\u043b\u0438\u0442\u044c \u043f\u0440\u0435\u0434\u0432\u0430\u0440\u0438\u0442\u0435\u043b\u044c\u043d\u044b\u0439 \u043f\u0435\u0440\u0432\u0438\u0447\u043d\u044b\u0439 \u043a\u043b\u044e\u0447 (pre-master), \u043a\u043e\u0442\u043e\u0440\u044b\u0439 \u043c\u043e\u0436\u043d\u043e \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u044c \u0434\u043b\u044f \u0440\u0430\u0441\u0448\u0438\u0444\u0440\u043e\u0432\u043a\u0438 TLS-\u0441\u043e\u0435\u0434\u0438\u043d\u0435\u043d\u0438\u0439, \u0432 \u0442\u043e\u043c \u0447\u0438\u0441\u043b\u0435 HTTPS, \u043f\u0440\u0438 \u043f\u0435\u0440\u0435\u0445\u0432\u0430\u0442\u0435 \u0442\u0440\u0430\u043d\u0437\u0438\u0442\u043d\u043e\u0433\u043e \u0442\u0440\u0430\u0444\u0438\u043a\u0430 (MITM). \u041e\u0442\u043c\u0435\u0447\u0430\u0435\u0442\u0441\u044f, \u0447\u0442\u043e \u0430\u0442\u0430\u043a\u0430 \u043e\u0447\u0435\u043d\u044c \u0441\u043b\u043e\u0436\u043d\u0430 \u0434\u043b\u044f \u043f\u0440\u0430\u043a\u0442\u0438\u0447\u0435\u0441\u043a\u043e\u0439 \u0440\u0435\u0430\u043b\u0438\u0437\u0430\u0446\u0438\u0438 \u0438 \u0431\u043e\u043b\u044c\u0448\u0435 \u043d\u043e\u0441\u0438\u0442 \u0442\u0435\u043e\u0440\u0435\u0442\u0438\u0447\u0435\u0441\u043a\u0438\u0439 \u0445\u0430\u0440\u0430\u043a\u0442\u0435\u0440. \u0414\u043b\u044f \u043f\u0440\u043e\u0432\u0435\u0434\u0435\u043d\u0438\u044f \u0430\u0442\u0430\u043a\u0438 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":93918,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-93917","post","type-post","status-publish","format-standard","has-post-thumbnail","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\udd47TLS-sebezhet\u0151s\u00e9gr\u0151l, amely lehet\u0151v\u00e9 teszi a DH titkos\u00edt\u00e1ssal m\u0171k\u00f6d\u0151 kapcsolatok kulcs\u00e1nak meghat\u00e1roz\u00e1s\u00e1t | ProHoster","description":"Felt\u00e1rultak r\u00e9szletek egy 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