{"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\/et\/blog\/news\/uyazvimost-v-tls-dopuskayushhaya-opredelenie-klyucha-dlya-soedinenij-na-baze-shifrov-dh","title":{"rendered":"TLS-i haavatavus, mis v\u00f5imaldab toimetada v\u00f5tme m\u00e4\u00e4ramist DH kr\u00fcpteerimise p\u00f5hjal olevate \u00fchenduste jaoks","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Avalikustatud<\/a><\/noindex> uus teave haavatavusest<\/a><\/noindex> (CVE-2020-1968) TLS-protokollis, mille koodnimi on
\nRaccoon<\/a><\/noindex> ja mis v\u00f5imaldab harvadel juhtudel tuvastada esialgse eelv\u00f5tme (pre-master), mida saab kasutada TLS-\u00fchenduste, sealhulgas HTTPS, dekr\u00fcptimiseks, kui vahepealsed andmed on p\u00fc\u00fctud (MITM). T\u00f5detakse, et r\u00fcnnak on praktiliselt raske ellu viia ja on pigem teoreetiline. R\u00fcnnaku l\u00e4biviimiseks on vajalik spetsiifiline TLS-serveri konfigureerimine ja v\u00e4ga t\u00e4pne ajam\u00f5\u00f5tmine serveri operatsioonide t\u00f6\u00f6tlemise ajal.<\/p>\n

Probleem on seotud TLS-spetsifikatsiooniga ja see m\u00f5jutab ainult \u00fchendusi, mis kasutavad DH (Diffie-Hellman, TLS_DH_*») p\u00f5hinevaid kr\u00fcptov\u00f5tme vahetuse \u0161ifreid. ECDH-\u0161ifrite puhul probleem ei ilmne ja need j\u00e4\u00e4vad ohutuks. S\u00fcsteemid, mis kasutavad TLS protokolle kuni versioonini 1.2, on haavatavad, kuid TLS 1.3 ei ole sellele probleemile vastuv\u00f5tlik. Haavatavus ilmneb TLS-i rakendustes, mis korduvkasutavad DH salajast v\u00f5tit erinevates TLS-\u00fchendustes (sellist k\u00e4itumist t\u00e4heldatakse ligikaudu 4.4% Alexa Top 1M serveritest).<\/p>\n

OpenSSL 1.0.2e ja varasemates v\u00e4ljaannetes korduvkasutatakse DH peav\u00f5tit k\u00f5igis serveri\u00fchendustes, kui ei ole selges\u00f5naliselt seatud valikut SSL_OP_SINGLE_DH_USE. Alates OpenSSL 1.0.2f korduvkasutatakse DH peav\u00f5tit ainult staatiliste DH-\u0161ifrite («DH-*», n\u00e4iteks «DH-RSA-AES256-SHA») kasutamisel. OpenSSL 1.1.1 puhul probleem ei ilmne, kuna selles versioonis ei kasutata DH peav\u00f5tit ja staatilisi DH-\u0161ifreid ei rakendata. <\/p>\n

DH v\u00f5tmemeetodi kasutamisel genereerivad m\u00f5lemad \u00fchenduse pooled juhuslikud privaatv\u00f5tmed (edaspidi v\u00f5ti «a» ja v\u00f5ti «b»), mille p\u00f5hjal arvutatakse ja saadetakse avalikud v\u00f5tmed (ga mod p ja gb mod p). P\u00e4rast avalike v\u00f5tmete saamist arvutab iga pool \u00fchise aluseks oleva v\u00f5tme (gab mod p), mida kasutatakse sessiooniv\u00f5tmete vormimiseks. Raccoon r\u00fcnnak v\u00f5imaldab aluseks oleva v\u00f5tme m\u00e4\u00e4ramist, anal\u00fc\u00fcsides teavet k\u00f5rvalkanalite kaudu, toetudes sellele, et TLS spetsifikatsioonides, sealhulgas versioon 1.2, n\u00f5utakse aluseks oleva v\u00f5tme k\u00f5ikide algsete nullbaitide k\u00f5rvaldamist enne selle kaasamist arvutustesse.<\/p>\n

Seal hulgas edastatakse k\u00e4rbitud algsusv\u00f5ti sessiooniv\u00f5tme genereerimise funktsiooni, mis p\u00f5hineb erineva viivitusega r\u00e4si funktsioonidel, mis t\u00f6\u00f6tlevad erinevaid andmeid. T\u00e4psed ajam\u00f5\u00f5tmised serveri toimingute ajal v\u00f5tmega v\u00f5imaldavad r\u00fcndajal kindlaks teha vihjeid (oracle), mis annavad v\u00f5imaluse otsustada, kas algsusv\u00f5ti algab nullist v\u00f5i mitte. N\u00e4iteks v\u00f5ib r\u00fcndaja kinni p\u00fc\u00fcda kliendi edastatud avaliku v\u00f5tme (ga), edastada selle serverisse ja m\u00e4\u00e4rata
\nkas tulemuseks olev algsusv\u00f5ti algab nullist.<\/p>\n

Kuigi \u00fcksi \u00fche baidi v\u00f5tme m\u00e4\u00e4ratlemine ei anna midagi, suudab r\u00fcndaja, kes pealtkuulab kliendi \u00fchenduse loomise k\u00e4igus edastatud v\u00e4\u00e4rtust «ga», genereerida komplekti teisi v\u00e4\u00e4rtusi, mis on seotud «ga» ja saata need serverisse eraldi \u00fchenduse loomise seanssides. Formeerides ja edastades v\u00e4\u00e4rtusi «gri*ga», suudab r\u00fcndaja serveri vastuse viivituste anal\u00fc\u00fcsi abil m\u00e4\u00e4rata v\u00e4\u00e4rtused, mis viivad algsete v\u00f5tmete saamiseni, alustades nullist. M\u00e4\u00e4rates sellised v\u00e4\u00e4rtused, suudab r\u00fcndaja koostada v\u00f5rrandite komplekti, et ilusas pakendis.<\/a><\/noindex> peidetud numbrite probleemid<\/a><\/noindex> ja arvutada algne peamine v\u00f5ti. <\/p>\n

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

OpenSSL-i haavatavused m\u00e4\u00e4ratud<\/a><\/noindex> madal oht, ning parandamine piirdus probleemsete «TLS_DH_*» \u0161ifrikoode versioonis 1.0.2w vaikimisi keelatud n\u00f5rkade \u0161ifrite kategooriasse jagamisega («weak-ssl-ciphers»). Sarnase l\u00e4henemise rakendasid ka Mozilla arendajad, kes v\u00e4lja l\u00fclitatud<\/a><\/noindex> NSS raamatukogus, mida kasutab Firefox, DH ja DHE kr\u00fcpteerimiste kogumid. Alates Firefox 78-st on probleemsed kr\u00fcpteerimised v\u00e4lja l\u00fclitatud. Chrome'is l\u00f5petati DH toe pakkumine juba 2016. aastal. BearSSL, BoringSSL, Botan, Mbed TLS ja s2n raamatukogud ei ole probleemi all, kuna nad ei toeta DH kr\u00fcpteerimisi ega statsioonilisi DH kr\u00fcpteerimiste variante. <\/p>\n

Eriliselt m\u00e4rgitakse t\u00e4iendavad probleemid (CVE-2020-5929<\/a><\/noindex>) F5 BIG-IP seadmete TLS-stekis, muutes r\u00fcnnaku reaalsemaks. Eriti avastati seadmete k\u00e4itumises k\u00f5rvalekaldeid, kui algse v\u00f5tme alguses on nullbaiti, mida saab kasutada t\u00e4pselt ajaviivitusm\u00f5\u00f5tmete asemel arvutuste tegemisel.<\/p>\n

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

Allikas: 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 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