Je k dispozici opraven\u00e1 verze OpenSSH 9.9p2, kter\u00e1 odstra\u0148uje dv\u011b zranitelnosti identifikovan\u00e9 spole\u010dnost\u00ed Qualys. Byla p\u0159edvedena uk\u00e1zka vyu\u017eit\u00ed t\u011bchto zranitelnost\u00ed k proveden\u00ed MITM \u00fatoku, kter\u00fd umo\u017e\u0148uje p\u0159i pokusu klienta o p\u0159ipojen\u00ed k SSH serveru p\u0159esm\u011brovat provoz na vlastn\u00ed fale\u0161n\u00fd server, obej\u00edt kontrolu hostitelsk\u00fdch kl\u00ed\u010d\u016f a vytvo\u0159it tak dojem, \u017ee klient se p\u0159ipojuje k po\u017eadovan\u00e9mu serveru (ssh klient p\u0159ijme hostitelsk\u00fd kl\u00ed\u010d fale\u0161n\u00e9ho serveru nam\u00edsto kl\u00ed\u010de leg\u00e1ln\u00edho serveru). <\/p>\n
Prvn\u00ed zranitelnost (CVE-2025-26465) je zp\u016fsobena logickou chybou v n\u00e1stroji ssh, kter\u00e1 umo\u017e\u0148uje obej\u00edt identifikaci serveru a prov\u00e9st MITM \u00fatok. Probl\u00e9m se projevuje od verze OpenSSH 6.8p1 (prosinec 2014) v konfigurac\u00edch se zapnut\u00fdm nastaven\u00edm VerifyHostKeyDNS. V z\u00e1kladn\u00ed instalaci OpenSSH je tato volba ve v\u00fdchoz\u00edm nastaven\u00ed vypnuta, av\u0161ak do b\u0159ezna 2023 byla v nastaven\u00edch ssh ve FreeBSD zapnuta. <\/p>\n
J\u00e1drem probl\u00e9mu je, \u017ee v k\u00f3du funkce verify_host_key_callback() p\u0159i vol\u00e1n\u00ed funkce verify_host_key() je kontrolov\u00e1n pouze chybov\u00fd k\u00f3d «-1», zat\u00edmco jin\u00e9 k\u00f3dy, jako «-2», jsou ignorov\u00e1ny. V d\u016fsledku toho funkce verify_host_key_callback() m\u016f\u017ee vr\u00e1tit \u00fasp\u011b\u0161n\u00fd k\u00f3d «0», i kdy\u017e funkce verify_host_key() vr\u00e1tila chybu «-2». Chybov\u00fd k\u00f3d «-2» je vr\u00e1cen funkc\u00ed verify_host_key() p\u0159i nedostatku pam\u011bti. Pokud se vytvo\u0159\u00ed podm\u00ednky, kter\u00e9 zp\u016fsob\u00ed neschopnost alokovat pam\u011b\u0165 ve funkci verify_host_key(), SSH p\u0159edpokl\u00e1d\u00e1, \u017ee hostitelsk\u00fd kl\u00ed\u010d byl \u00fasp\u011b\u0161n\u011b ov\u011b\u0159en. K vytvo\u0159en\u00ed takov\u00fdch podm\u00ednek \u00fato\u010dn\u00fd SSH server, na kter\u00fd je klient p\u0159esm\u011brov\u00e1n, vrac\u00ed hostitelsk\u00fd kl\u00ed\u010d maxim\u00e1ln\u00ed mo\u017en\u00e9 velikosti (256 KB) a z\u00e1rove\u0148 se vyu\u017e\u00edv\u00e1 \u00fanik pam\u011bti na stran\u011b ssh klienta. <\/p>\n
Podm\u00ednky pro vytvo\u0159en\u00ed \u00faniku pam\u011bti jsou dosa\u017eeny d\u00edky druh\u00e9 zranitelnosti (CVE-2025-26466), kter\u00e1 zasahuje jak klienta ssh, tak server<\/a> sshd, a provozuje se bez autentizace. Zranitelnost umo\u017e\u0148uje vy\u010derpat dostupnou pam\u011b\u0165 procesu a vytvo\u0159it vysokou z\u00e1t\u011b\u017e CPU zasl\u00e1n\u00edm velk\u00e9ho po\u010dtu paket\u016f SSH2_MSG_PING. V zpracovateli paket\u016f SSH2_MSG_PING je \u00fanik pam\u011bti, kter\u00fd se projevuje od verze OpenSSH 9.5p1 (srpen 2023). \u00danik nast\u00e1v\u00e1 t\u00edm, \u017ee pro ka\u017ed\u00fd p\u0159ijat\u00fd 16-bajtov\u00fd PING paket se alokuje 256-bajtov\u00fd buffer pro vytvo\u0159en\u00ed odpov\u011bdi, ale tento buffer je uvoln\u011bn a\u017e po dokon\u010den\u00ed dojedn\u00e1v\u00e1n\u00ed kl\u00ed\u010d\u016f. Jako obranou cestou se doporu\u010duje nastavit omezen\u00ed pomoc\u00ed direktiv LoginGraceTime, MaxStartups a PerSourcePenalties. \u0414\u043e\u0441\u0442\u0443\u043f\u0435\u043d \u043a\u043e\u0440\u0440\u0435\u043a\u0442\u0438\u0440\u0443\u044e\u0449\u0438\u0439 \u0432\u044b\u043f\u0443\u0441\u043a OpenSSH 9.9p2, \u0432 \u043a\u043e\u0442\u043e\u0440\u043e\u043c \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u044b \u0434\u0432\u0435 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438, \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043d\u044b\u0435 \u043a\u043e\u043c\u043f\u0430\u043d\u0438\u0435\u0439 Qualys. \u041f\u0440\u043e\u0434\u0435\u043c\u043e\u043d\u0441\u0442\u0440\u0438\u0440\u043e\u0432\u0430\u043d \u043f\u0440\u0438\u043c\u0435\u0440 \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u043d\u0438\u044f \u0434\u0430\u043d\u043d\u044b\u0445 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0435\u0439 \u0434\u043b\u044f \u0441\u043e\u0432\u0435\u0440\u0448\u0435\u043d\u0438\u044f MITM-\u0430\u0442\u0430\u043a\u0438, \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0435\u0439 \u043f\u0440\u0438 \u043f\u043e\u043f\u044b\u0442\u043a\u0435 \u043f\u043e\u0434\u043a\u043b\u044e\u0447\u0435\u043d\u0438\u044f \u043a\u043b\u0438\u0435\u043d\u0442\u0430 \u043a SSH-\u0441\u0435\u0440\u0432\u0435\u0440\u0443, \u043f\u0435\u0440\u0435\u043d\u0430\u043f\u0440\u0430\u0432\u0438\u0442\u044c \u0442\u0440\u0430\u0444\u0438\u043a \u043d\u0430 \u0441\u043e\u0431\u0441\u0442\u0432\u0435\u043d\u043d\u044b\u0439 \u0444\u0438\u043a\u0442\u0438\u0432\u043d\u044b\u0439 \u0441\u0435\u0440\u0432\u0435\u0440, \u043e\u0431\u043e\u0439\u0442\u0438 \u043f\u0440\u043e\u0432\u0435\u0440\u043a\u0443 \u0445\u043e\u0441\u0442\u043e\u0432\u044b\u0445 \u043a\u043b\u044e\u0447\u0435\u0439 \u0438 \u0441\u043e\u0437\u0434\u0430\u0442\u044c \u0443 \u043a\u043b\u0438\u0435\u043d\u0442\u0430 \u0432\u0438\u0434\u0438\u043c\u043e\u0441\u0442\u044c \u043f\u043e\u0434\u043a\u043b\u044e\u0447\u0435\u043d\u0438\u044f \u043a \u0436\u0435\u043b\u0430\u0435\u043c\u043e\u043c\u0443 \u0441\u0435\u0440\u0432\u0435\u0440\u0443 (ssh-\u043a\u043b\u0438\u0435\u043d\u0442 \u043f\u0440\u0438\u043c\u0435\u0442 \u0445\u043e\u0441\u0442\u043e\u0432\u044b\u0439 \u043a\u043b\u044e\u0447 \u0444\u0438\u043a\u0442\u0438\u0432\u043d\u043e\u0433\u043e \u0441\u0435\u0440\u0432\u0435\u0440\u0430 \u0432\u043c\u0435\u0441\u0442\u043e \u043a\u043b\u044e\u0447\u0430 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Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"