{"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 vulnerabiilsus, mis v\u00f5imaldab m\u00e4\u00e4rata v\u00f5tme DH-protokollide p\u00f5hjal","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Ava<\/a><\/noindex> teave uue haavatavuse<\/a><\/noindex> (CVE-2020-1968) TLS-protokollis, mille koodnimi on
\nRaccoon<\/a><\/noindex> ja mis v\u00f5imaldab v\u00e4ga harvaesinevate asjaolude korral m\u00e4\u00e4rata eelmise peamise v\u00f5tme (pre-master), mida saab kasutada TLS-\u00fchenduste, sealhulgas HTTPS-i, dekr\u00fcpteerimiseks, kui vahepealset liiklust (MITM) tabatakse. Tuuakse esile, et r\u00fcnnak on praktilise teostamise osas v\u00e4ga keeruline ja on pigem teoreetilise iseloomuga. R\u00fcnnaku teostamiseks on vajalik TLS-serveri spetsiifiline konfiguratsioon ja v\u00f5ime v\u00e4ga t\u00e4pselt m\u00f5\u00f5ta serveri operatsioonide t\u00f6\u00f6tlemise aega.<\/p>\n

Probleem on otse TLS spetsifikatsioonis ja see puudutab ainult \u00fchendusi, mis kasutavad DH (Diffie-Hellman, TLS_DH_*») p\u00f5hinevaid \u0161ifreid. ECDH \u0161ifrite puhul probleem ei ilmne ja need j\u00e4\u00e4vad turvaliseks. Haavatavad on ainult TLS protokollid kuni versioonini 1.2, TLS 1.3 ei ole sellele probleemile allutatav. Haavatavus avaldub TLS-i rakendustes, mis kasutavad erinevates TLS-\u00fchendustes sama DH salajast v\u00f5tit (sarnast k\u00e4itumist t\u00e4heldatakse umbes 4.4% Alexa Top 1M serveritest).<\/p>\n

OpenSSL 1.0.2e ja varasemates versioonides taastatakse DH algv\u00f5ti k\u00f5igis serveri \u00fchendustes, kui valik SSL_OP_SINGLE_DH_USE ei ole selgelt m\u00e4\u00e4ratud. Alates OpenSSL 1.0.2f taastatakse DH algv\u00f5ti ainult staatiliste DH-\u0161ifrite kasutamisel («DH-*», n\u00e4iteks «DH-RSA-AES256-SHA»). OpenSSL 1.1.1 puhul haavatavus ei avaldu, kuna sellel harul ei kasutata DH algv\u00f5tit ega rakendata staatilisi DH-\u0161ifreid. <\/p>\n

DH v\u00f5tmise meetodi kasutamisel genereerivad \u00fchenduse m\u00f5lemad pooled juhuslikud salajased v\u00f5tmised (edasi on v\u00f5tmed «a» ja «b»), mille alusel arvutatakse ja saadetakse avalikud v\u00f5tmed (ga mod p ja gb mod p). P\u00e4rast iga poolepoolsete avalike v\u00f5tmete vastuv\u00f5tmist arvutab kummagi osapoole poolt \u00fchine algv\u00f5ti (gab mod p), mida rakendatakse seansi v\u00f5tmete moodustamiseks. Raccooni r\u00fcnnak v\u00f5imaldab tuvastada algv\u00f5tit, anal\u00fc\u00fcsides kolmandate kanalite kaudu saadud teavet, tuginedes sellele, et TLS-i spetsifikatsioonides kuni versioonini 1.2 k\u00e4stakse enne arvutusi algv\u00f5tme nullbaiid k\u00f5rvale j\u00e4tta.<\/p>\n

Seal, sealitud esialgne v\u00f5ti edastatakse seansi v\u00f5tme genereerimise funktsiooni, mis p\u00f5hineb erineva viivituse ajal erinevate andmete t\u00f6\u00f6tlemisel. Serveri operatsioonide aja t\u00e4psete m\u00f5\u00f5tmiste abil suudab r\u00fcndaja leida vihjeid (oracle), mis annavad v\u00f5imaluse hinnata, kas esialgne v\u00f5ti algab nullist v\u00f5i mitte. N\u00e4iteks v\u00f5ib r\u00fcndaja r\u00f6\u00f6vida kliendi edastatud avaliku v\u00f5tme (ga), saata selle serverisse tagasi ja kindlaks teha
\nkas tulemuseks olev esialgne v\u00f5ti algab nullist.<\/p>\n

\u00dche algv\u00f5tme baidi m\u00e4\u00e4ramine iseenesest ei anna midagi, kuid kui r\u00fcndaja j\u00e4\u00e4b klientelt edastatud 'ga' v\u00e4\u00e4rtust s\u00f5lmimisprotsessis kinni, v\u00f5ib ta luua komplekti muid 'ga' v\u00e4\u00e4rtustega seotud v\u00e4\u00e4rtusi ja saata need serverisse eraldi s\u00f5lmimisprotsessides. Luues ja edastades v\u00e4\u00e4rtusi 'gri*ga', suudab r\u00fcndaja anal\u00fc\u00fcsida serveri vastuse viivituse muutusi, et tuvastada v\u00e4\u00e4rtusi, mis toovad esile algv\u00f5tmed, mis hakkavad nullist. Tuvastades selliseid v\u00e4\u00e4rtusi, v\u00f5ib r\u00fcndaja koostada v\u00f5rrandite komplekti. otsuse<\/a><\/noindex> peidetud arvude probleemile<\/a><\/noindex> ja arvutada algse esialgse v\u00f5tme. <\/p>\n

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

OpenSSL on haavatavuste on omistatud<\/a><\/noindex> madal ohtude tase ning probleemsete \u0161ifriste «TLS_DH_*» liigutamine v\u00e4lja l\u00fclitatud vaikeseade kategooriasse, millel on ebapiisav kaitsetase («weak-ssl-ciphers»). Samamoodi k\u00e4itusid ka Mozilla arendajad, kes deaktiveerisid<\/a><\/noindex> NSS-kogus, mida kasutatakse Firefoxis, DH ja DHE kr\u00fcptoalgoritmide hulgad. Alates Firefox 78 on probleemsed \u0161ifrid keelatud. Chrome'is l\u00f5petati DH toetus juba 2016. aastal. BearSSL, BoringSSL, Botan, Mbed TLS ja s2n ei ole selle probleemi suhtes haavatavad, kuna nad ei toeta DH algoritme ega nende staatilisi variante. <\/p>\n

Erilised t\u00e4iendavad probleemid on v\u00e4lja toodud (CVE-2020-5929<\/a><\/noindex>) F5 BIG-IP seadmete TLSi virnas, mis muudab r\u00fcnnaku realistlikumaks. Eelk\u00f5ige on tuvastatud k\u00f5rvalekalded seadmete k\u00e4itumises, kui esialgse v\u00f5tme alguses on nullbyte, mida saab kasutada t\u00e4psete ajaviivituste m\u00f5\u00f5tmise asemel.<\/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 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