Wydano poprawk\u0119 do OpenSSH 9.9p2, w kt\u00f3rej usuni\u0119to dwie podatno\u015bci wykryte przez firm\u0119 Qualys. Zaprezentowano przyk\u0142ad wykorzystania tych podatno\u015bci do przeprowadzenia ataku MITM, kt\u00f3ry umo\u017cliwia przechwycenie ruchu, gdy klient pr\u00f3buje po\u0142\u0105czy\u0107 si\u0119 z serwerem SSH, przekierowuj\u0105c go na fa\u0142szywy serwer oraz obejmuj\u0105c weryfikacj\u0119 kluczy hosta, tworz\u0105c u klienta iluzj\u0119 po\u0142\u0105czenia z po\u017c\u0105danym serwerem (klient SSH zaakceptuje klucz hosta fa\u0142szywego serwera zamiast klucza legalnego serwera). <\/p>\n
Pierwsza podatno\u015b\u0107 (CVE-2025-26465) wynika z b\u0142\u0119du logicznego w narz\u0119dziu ssh, kt\u00f3ry pozwala obej\u015b\u0107 weryfikacj\u0119 identyfikacji serwera i przeprowadzi\u0107 atak MITM. Problem pojawia si\u0119 od wydania OpenSSH 6.8p1 (grudzie\u0144 2014 r.) w konfiguracjach z w\u0142\u0105czon\u0105 opcj\u0105 VerifyHostKeyDNS. W standardowej instalacji OpenSSH ta opcja domy\u015blnie jest wy\u0142\u0105czona, ale do marca 2023 roku by\u0142a w\u0142\u0105czona w ustawieniach ssh w FreeBSD. <\/p>\n
Istot\u0105 problemu jest to, \u017ce w kodzie funkcji verify_host_key_callback() podczas wywo\u0142ania funkcji verify_host_key() sprawdzany jest tylko kod b\u0142\u0119du «-1», podczas gdy inne kody, takie jak «-2», s\u0105 ignorowane. W konsekwencji funkcja verify_host_key_callback() mo\u017ce zwr\u00f3ci\u0107 pomy\u015blny kod «0», mimo \u017ce funkcja verify_host_key() zg\u0142asza b\u0142\u0105d «-2». Kod b\u0142\u0119du «-2» jest zwracany przez funkcj\u0119 verify_host_key() w przypadku braku pami\u0119ci. Je\u015bli zostan\u0105 stworzone warunki, kt\u00f3re uniemo\u017cliwiaj\u0105 przydzielenie pami\u0119ci w funkcji verify_host_key(), SSH uzna, \u017ce klucz hosta zosta\u0142 pomy\u015blnie zweryfikowany. Aby stworzy\u0107 takie warunki, oszuka\u0144cze serwery SSH atakuj\u0105cego, na kt\u00f3re jest przekierowany klient, zwracaj\u0105 klucz hosta o maksymalnym rozmiarze (256KB) i jednocze\u015bnie wykorzystuj\u0105 wyciek pami\u0119ci po stronie klienta SSH. <\/p>\n
Warunki do stworzenia usterki pami\u0119ci s\u0105 osi\u0105gane dzi\u0119ki drugiej podatno\u015bci (CVE-2025-26466), kt\u00f3ra dotyczy zar\u00f3wno klienta ssh, jak i serwer<\/a> sshd, i eksploatowane bez uwierzytelnienia. Wra\u017cliwo\u015b\u0107 pozwala na wyczerpanie dost\u0119pnej pami\u0119ci procesora i stworzenie du\u017cego obci\u0105\u017cenia CPU poprzez wys\u0142anie du\u017cej liczby pakiet\u00f3w SSH2_MSG_PING. W obs\u0142udze pakiet\u00f3w SSH2_MSG_PING wyst\u0119puje wyciek pami\u0119ci, kt\u00f3ry pojawia si\u0119 od wydania OpenSSH 9.5p1 (sierpie\u0144 2023 r.). Wyciek wyst\u0119puje, poniewa\u017c dla ka\u017cdego przychodz\u0105cego 16-bajtowego pakietu PING przydzielany jest 256-bajtowy bufor do formowania odpowiedzi, ale ten bufor jest zwalniany dopiero po zako\u0144czeniu negocjacji kluczy. Jako rozwi\u0105zanie ochrony proponuje si\u0119 skonfigurowanie ogranicze\u0144 za pomoc\u0105 dyrektyw LoginGraceTime, MaxStartups i 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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\u0179r\u00f3d\u0142o: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"