A kaliforniai Riverside Egyetem kutat\u00f3csoportja k\u00f6zz\u00e9tette a SAD DNS (CVE-2021-20322) \u00faj t\u00e1mad\u00e1si vari\u00e1ns\u00e1t, amely a tavaly bevezetett v\u00e9delem ellen\u00e9re is m\u0171k\u00f6dik, hogy blokkolja a CVE-2020-25705 s\u00e9r\u00fcl\u00e9kenys\u00e9get. Az \u00faj m\u00f3dszer alapvet\u0151en hasonl\u00f3 a tavalyi s\u00e9r\u00fcl\u00e9kenys\u00e9ghez, \u00e9s csup\u00e1n annyiban k\u00fcl\u00f6nb\u00f6zik, hogy m\u00e1s t\u00edpus\u00fa ICMP-csomagokat haszn\u00e1l az akt\u00edv UDP-portok ellen\u0151rz\u00e9s\u00e9re. A javasolt t\u00e1mad\u00e1s lehet\u0151v\u00e9 teszi hamis adatok behelyettes\u00edt\u00e9s\u00e9t a DNS-szerver gyors\u00edt\u00f3t\u00e1r\u00e1ba, amelyet arra lehet haszn\u00e1lni, hogy egy tetsz\u0151leges domain IP-c\u00edm\u00e9t \u00e1t\u00edrja a gyors\u00edt\u00f3t\u00e1rban, ezzel a domainhez int\u00e9zett k\u00e9r\u00e9seket a t\u00e1mad\u00f3 szerver\u00e9re ir\u00e1ny\u00edtja. <\/p>\n
A javasolt m\u00f3dszer csak a Linux h\u00e1l\u00f3zati verem\u00e9ben m\u0171k\u00f6dik, mivel a Linuxban az ICMP-csomagok feldolgoz\u00e1si mechanizmus\u00e1nak saj\u00e1toss\u00e1g\u00e1hoz k\u00f6t\u0151dik, amely az adatsziv\u00e1rg\u00e1s forr\u00e1sa, egyszer\u0171s\u00edtve az UDP-port sz\u00e1m\u00e1nak meghat\u00e1roz\u00e1s\u00e1t, amelyet haszn\u00e1ltak szerverrel<\/a> a k\u00fcls\u0151 k\u00e9r\u00e9s elk\u00fcld\u00e9s\u00e9re. Az inform\u00e1ci\u00f3sziv\u00e1rg\u00e1s blokkol\u00e1s\u00e1ra vonatkoz\u00f3 m\u00f3dos\u00edt\u00e1sokat a Linux kernelbe augusztus v\u00e9g\u00e9n vezett\u00e9k be (a jav\u00edt\u00e1s a 5.15-\u00f6s kernelbe \u00e9s a szeptemberi LTS-\u00e1g friss\u00edt\u00e9seibe ker\u00fclt). A jav\u00edt\u00e1s l\u00e9nyege, hogy a h\u00e1l\u00f3zati gyors\u00edt\u00f3t\u00e1rakban a SipHash hash algoritmus haszn\u00e1lat\u00e1ra t\u00e9rnek \u00e1t a Jenkins Hash helyett. A s\u00e9r\u00fcl\u00e9kenys\u00e9g jav\u00edt\u00e1s\u00e1nak \u00e1llapota a disztrib\u00faci\u00f3kban az al\u00e1bbi oldalakon \u00e9rt\u00e9kelhet\u0151: Debian, RHEL, Fedora, SUSE, Ubuntu. <\/p>\n A probl\u00e9m\u00e1t azonos\u00edt\u00f3 kutat\u00f3k adatai szerint a h\u00e1l\u00f3zaton tal\u00e1lhat\u00f3 ny\u00edlt felold\u00f3k k\u00f6r\u00fclbel\u00fcl 38%-a \u00e9rintett, bele\u00e9rtve a n\u00e9pszer\u0171 DNS-szolg\u00e1ltat\u00e1sokat, mint p\u00e9ld\u00e1ul az OpenDNS \u00e9s a Quad9 (9.9.9.9). A szerveroldali szoftver eset\u00e9ben a t\u00e1mad\u00e1s v\u00e9grehajthat\u00f3 Linux szerveren olyan csomagok haszn\u00e1lat\u00e1val, mint a BIND, Unbound \u00e9s dnsmasq. Windows \u00e9s BSD rendszerek haszn\u00e1lat\u00e1val fut\u00f3 DNS-szervereken a probl\u00e9ma nem jelentkezik. A t\u00e1mad\u00e1s sikeres v\u00e9grehajt\u00e1s\u00e1hoz IP-spoofing sz\u00fcks\u00e9ges, azaz a t\u00e1mad\u00f3 szolg\u00e1ltat\u00f3j\u00e1nak nem szabad blokkolnia a hamis forr\u00e1st jelent\u0151 IP-c\u00edmr\u0151l \u00e9rkez\u0151 csomagokat. <\/p>\n Eml\u00e9keztet\u00fcnk, hogy a SAD DNS t\u00e1mad\u00e1s lehet\u0151v\u00e9 teszi a DNS szerverek \u00e1ltal a klasszikus DNS cache poisoning m\u00f3dszer blokkol\u00e1s\u00e1ra bevezetett v\u00e9delem megker\u00fcl\u00e9s\u00e9t, amelyet 2008-ban Dan Kaminsky javasolt. Kaminsky m\u00f3dszere manipul\u00e1lja a DNS k\u00e9r\u00e9s azonos\u00edt\u00f3sz\u00e1m\u00e1nak mez\u0151j\u00e9t, amely mind\u00f6ssze 16 bit hossz\u00fa. A helyes DNS tranzakci\u00f3s azonos\u00edt\u00f3 kiv\u00e1laszt\u00e1s\u00e1hoz, amely a hosztn\u00e9v \u00e1lc\u00e1z\u00e1s\u00e1hoz sz\u00fcks\u00e9ges, k\u00f6r\u00fclbel\u00fcl 7000 k\u00e9rd\u00e9st kell elk\u00fcldeni, \u00e9s k\u00f6r\u00fclbel\u00fcl 140 ezer \u00e1l-v\u00e1laszt kell szimul\u00e1lni. A t\u00e1mad\u00e1s arra \u00f6sszpontos\u00edt, hogy a DNS resolverhez sok csomagot k\u00fcldj\u00f6n hamis IP t\u00e1rs\u00edt\u00e1ssal \u00e9s k\u00fcl\u00f6nb\u00f6z\u0151 DNS tranzakci\u00f3s azonos\u00edt\u00f3kkal. Annak megakad\u00e1lyoz\u00e1sa \u00e9rdek\u00e9ben, hogy az els\u0151 v\u00e1lasz cache-el\u00e9sre ker\u00fclj\u00f6n, minden hamis v\u00e1laszban egy kiss\u00e9 megv\u00e1ltoztatott domain nevet (1.example.com, 2.example.com, 3.example.com stb.) adunk meg. <\/p>\n A t\u00e1mad\u00e1s ezen form\u00e1ja ellen a DNS szerver gy\u00e1rt\u00f3i a DNS lek\u00e9rdez\u00e9sekhez haszn\u00e1lt kezd\u0151 h\u00e1l\u00f3zati portok v\u00e9letlenszer\u0171 allok\u00e1l\u00e1s\u00e1t val\u00f3s\u00edtott\u00e1k meg, ami kompenz\u00e1lta az azonos\u00edt\u00f3 m\u00e9ret\u00e9nek hi\u00e1ny\u00e1t. A v\u00e9delem megval\u00f3s\u00edt\u00e1sa ut\u00e1n ahhoz, hogy hamis v\u00e1laszt k\u00fcldj\u00fcnk, nemcsak a 16 bites azonos\u00edt\u00f3t kellett kital\u00e1lni, hanem egy a 64 ezer port k\u00f6z\u00fcl is, ami a lehet\u0151s\u00e9gek sz\u00e1m\u00e1t 2^32-re n\u00f6velte. <\/p>\n A SAD DNS m\u00f3dszer dr\u00e1maian leegyszer\u0171s\u00edti a h\u00e1l\u00f3zati port sz\u00e1m\u00e1nak meghat\u00e1roz\u00e1s\u00e1t, \u00e9s visszaford\u00edtja a t\u00e1mad\u00e1st a klasszikus Kaminsky-m\u00f3dszerre. A t\u00e1mad\u00f3 k\u00e9pes lehet felismerni a nem haszn\u00e1lt \u00e9s akt\u00edv UDP-portokat, kihaszn\u00e1lva a h\u00e1l\u00f3zati portok aktivit\u00e1s\u00e1r\u00f3l sz\u00f3l\u00f3 inform\u00e1ci\u00f3k sziv\u00e1rg\u00e1s\u00e1t az ICMP v\u00e1laszcsomagok feldolgoz\u00e1sa sor\u00e1n. A m\u00f3dszer lehet\u0151v\u00e9 teszi, hogy 4 nagys\u00e1grenddel cs\u00f6kkents\u00fck a lehets\u00e9ges kombin\u00e1ci\u00f3k sz\u00e1m\u00e1t \u2014 2^16+2^16 helyett 2^32 (131_072 helyett 4_294_967_296). Az inform\u00e1ci\u00f3k sziv\u00e1rg\u00e1sa, amelyek lehet\u0151v\u00e9 teszik az akt\u00edv UDP-portok gyors meghat\u00e1roz\u00e1s\u00e1t, a frakcion\u00e1l\u00e1si k\u00e9relmek ICMP-csomagok kezel\u00e9s\u00e9ben (ICMP Fragmentation Needed jelz\u0151) vagy az \u00e1tir\u00e1ny\u00edt\u00e1si k\u00e9relmekben (ICMP Redirect jelz\u0151) jelentkez\u0151 hib\u00e1kb\u00f3l ad\u00f3dik. Az ilyen csomagok k\u00fcld\u00e9se megv\u00e1ltoztatja a h\u00e1l\u00f3zati verem cache-\u00e1llapot\u00e1t, ami lehet\u0151v\u00e9 teszi a szerver reakci\u00f3j\u00e1nak alapj\u00e1n annak meg\u00e1llap\u00edt\u00e1s\u00e1t, hogy mely UDP-portok akt\u00edvak, \u00e9s melyek nem. <\/p>\n T\u00e1mad\u00e1si forgat\u00f3k\u00f6nyv: Amikor a DNS-ler\u00e1z\u00f3 megpr\u00f3b\u00e1lja meghat\u00e1rozni a domain nevet, UDP-k\u00e9rd\u00e9st k\u00fcld a DNS-szerverhez, amely a domain szolg\u00e1ltat\u00e1s\u00e1\u00e9rt felel\u0151s. Abban a pillanatban, amikor a ler\u00e1z\u00f3 v\u00e1rja a v\u00e1laszt, a t\u00e1mad\u00f3 gyorsan meghat\u00e1rozhatja a k\u00e9rd\u00e9s k\u00fcld\u00e9s\u00e9hez haszn\u00e1lt forr\u00e1shiport sz\u00e1m\u00e1t, \u00e9s hamis v\u00e1laszt k\u00fcldhet erre, eladva mag\u00e1t mint a domaint kiszolg\u00e1l\u00f3 DNS-szerver, hamis\u00edt\u00e1ssal. IP address<\/a>A DNS-ler\u00e1z\u00f3 a hamis v\u00e1laszban \u00e1tadott adatokat a gyors\u00edt\u00f3t\u00e1r\u00e1ba helyezi, \u00e9s egy ideig b\u00e1rmilyen m\u00e1s DNS-k\u00e9rd\u00e9sre, amely a domain n\u00e9vre vonatkozik, a t\u00e1mad\u00f3 \u00e1ltal megadott IP-c\u00edmet fogja visszaadni. \u0413\u0440\u0443\u043f\u043f\u0430 \u0438\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u0439 \u0438\u0437 \u041a\u0430\u043b\u0438\u0444\u043e\u0440\u043d\u0438\u0439\u0441\u043a\u043e\u0433\u043e \u0443\u043d\u0438\u0432\u0435\u0440\u0441\u0438\u0442\u0435\u0442\u0430 \u0432 \u0420\u0438\u0432\u0435\u0440\u0441\u0430\u0439\u0434\u0435 \u043e\u043f\u0443\u0431\u043b\u0438\u043a\u043e\u0432\u0430\u043b\u0430 \u043d\u043e\u0432\u044b\u0439 \u0432\u0430\u0440\u0438\u0430\u043d\u0442 \u0430\u0442\u0430\u043a\u0438 SAD DNS (CVE-2021-20322), \u0440\u0430\u0431\u043e\u0442\u0430\u044e\u0449\u0438\u0439 \u043d\u0435\u0441\u043c\u043e\u0442\u0440\u044f \u043d\u0430 \u0437\u0430\u0449\u0438\u0442\u0443, \u0434\u043e\u0431\u0430\u0432\u043b\u0435\u043d\u043d\u0443\u044e \u0432 \u043f\u0440\u043e\u0448\u043b\u043e\u043c \u0433\u043e\u0434\u0443 \u0434\u043b\u044f \u0431\u043b\u043e\u043a\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 CVE-2020-25705. \u041d\u043e\u0432\u044b\u0439 \u043c\u0435\u0442\u043e\u0434 \u0432 \u0446\u0435\u043b\u043e\u043c \u0430\u043d\u0430\u043b\u043e\u0433\u0438\u0447\u0435\u043d \u043f\u0440\u043e\u0448\u043b\u043e\u0433\u043e\u0434\u043d\u0435\u0439 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 \u0438 \u043e\u0442\u043b\u0438\u0447\u0430\u0435\u0442\u0441\u044f \u043b\u0438\u0448\u044c \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u043d\u0438\u0435\u043c \u0434\u0440\u0443\u0433\u043e\u0433\u043e \u0442\u0438\u043f\u0430 ICMP-\u043f\u0430\u043a\u0435\u0442\u043e\u0432 \u0434\u043b\u044f \u043f\u0440\u043e\u0432\u0435\u0440\u043a\u0438 \u0430\u043a\u0442\u0438\u0432\u043d\u044b\u0445 UDP-\u043f\u043e\u0440\u0442\u043e\u0432. \u041f\u0440\u0435\u0434\u043b\u043e\u0436\u0435\u043d\u043d\u0430\u044f \u0430\u0442\u0430\u043a\u0430 \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u0435\u0442 \u043e\u0441\u0443\u0449\u0435\u0441\u0442\u0432\u0438\u0442\u044c \u043f\u043e\u0434\u0441\u0442\u0430\u043d\u043e\u0432\u043a\u0443 \u0444\u0438\u043a\u0442\u0438\u0432\u043d\u044b\u0445 \u0434\u0430\u043d\u043d\u044b\u0445 \u0432 \u043a\u044d\u0448 DNS-\u0441\u0435\u0440\u0432\u0435\u0440\u0430, \u0447\u0442\u043e […]<\/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-102308","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\udd47\u00daj SAD DNS t\u00e1mad\u00e1si v\u00e1ltozat a DNS gyors\u00edt\u00f3t\u00e1rba hamis adatok besz\u00far\u00e1s\u00e1ra | ProHoster","description":"Egy kaliforniai egyetem Riverside-i kutat\u00f3csoportja k\u00f6zz\u00e9tette a SAD DNS (CVE-2021-20322) t\u00e1mad\u00e1s \u00faj v\u00e1ltozat\u00e1t, amely m\u0171k\u00f6dik annak ellen\u00e9re, hogy tavaly v\u00e9delmet vezettek be a kiszolg\u00e1l\u00f3 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\u043a\u044d\u0448 DNS | ProHoster","og:description":"\u0413\u0440\u0443\u043f\u043f\u0430 \u0438\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u0439 \u0438\u0437 \u041a\u0430\u043b\u0438\u0444\u043e\u0440\u043d\u0438\u0439\u0441\u043a\u043e\u0433\u043e \u0443\u043d\u0438\u0432\u0435\u0440\u0441\u0438\u0442\u0435\u0442\u0430 \u0432 \u0420\u0438\u0432\u0435\u0440\u0441\u0430\u0439\u0434\u0435 \u043e\u043f\u0443\u0431\u043b\u0438\u043a\u043e\u0432\u0430\u043b\u0430 \u043d\u043e\u0432\u044b\u0439 \u0432\u0430\u0440\u0438\u0430\u043d\u0442 \u0430\u0442\u0430\u043a\u0438 SAD DNS (CVE-2021-20322), \u0440\u0430\u0431\u043e\u0442\u0430\u044e\u0449\u0438\u0439 \u043d\u0435\u0441\u043c\u043e\u0442\u0440\u044f \u043d\u0430 \u0437\u0430\u0449\u0438\u0442\u0443, \u0434\u043e\u0431\u0430\u0432\u043b\u0435\u043d\u043d\u0443\u044e \u0432 \u043f\u0440\u043e\u0448\u043b\u043e\u043c \u0433\u043e\u0434\u0443 \u0434\u043b\u044f \u0431\u043b\u043e\u043a\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u044f 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