Der er blevet udgivet en korrektionsopdatering til OpenSSH 9.9p2, som udbedrer to s\u00e5rbarheder identificeret af Qualys. Et eksempel p\u00e5 udnyttelse af disse s\u00e5rbarheder til en MITM-angreb er blevet demonstretreret, hvilket muligg\u00f8r, at trafik kan omdirigeres til en falsk server, n\u00e5r en klient fors\u00f8ger at oprette forbindelse til en SSH-server. Dette kan omg\u00e5 kontrollen af v\u00e6rtens n\u00f8gler og give klienten indtryk af, at den er forbundet til den \u00f8nskede server (SSH-klienten vil acceptere den falske servers v\u00e6rtens n\u00f8gle i stedet for den legitime servers n\u00f8gle). <\/p>\n
Den f\u00f8rste s\u00e5rbarhed (CVE-2025-26465) skyldes en logisk fejl i ssh-v\u00e6rkt\u00f8jet, der muligg\u00f8r omg\u00e5else af serveridentifikation og gennemf\u00f8relse af et MITM-angreb. Problemet opst\u00e5r fra og med udgivelsen af OpenSSH 6.8p1 (december 2014) i konfigurationer med den aktiverede indstilling VerifyHostKeyDNS. I den grundl\u00e6ggende installation af OpenSSH er denne indstilling som standard deaktiveret, men var aktiveret i ssh-indstillingerne p\u00e5 FreeBSD frem til marts 2023. <\/p>\n
Kernen i problemet er, at i koden til funktionen verify_host_key_callback() kontrolleres kun fejlkoden «-1», mens andre koder som «-2» ignoreres. Resultatet er, at funktionen verify_host_key_callback() kan returnere en succesfuld kode «0», p\u00e5 trods af at der er returneret en fejl «-2» fra funktionen verify_host_key(). Fejlkoden «-2» returneres af funktionen verify_host_key() ved hukommelsesmangel. Hvis man skaber forhold, der f\u00f8rer til, at det ikke er muligt at tildele hukommelse i funktionen verify_host_key(), vil SSH tro, at v\u00e6rtsn\u00f8glen blev verificeret med succes. For at skabe s\u00e5danne forhold returnerer en falsk SSH-server fra angriberen, som klienten omdirigeres til, v\u00e6rtsn\u00f8glen i den maksimale st\u00f8rrelse (256KB), samtidig med at der udnyttes et hukommelsesl\u00e6k p\u00e5 ssh-klientens side. <\/p>\n
Betingelserne for at skabe hukommelsestabet opn\u00e5s gennem den anden s\u00e5rbarhed (CVE-2025-26466), der ber\u00f8rer b\u00e5de ssh-klienten og server<\/a> sshd, og k\u00f8rer uden autentifikation. S\u00e5rbarheden tillader udt\u00f8mning af den tilg\u00e6ngelige proces hukommelse og skaber en h\u00f8j belastning p\u00e5 CPU'en ved at sende et stort antal SSH2_MSG_PING pakker. I h\u00e5ndteringen af SSH2_MSG_PING pakkerne er der et hukommelsesl\u00e6k, der viser sig fra udgivelsen af OpenSSH 9.5p1 (august 2023). L\u00e6kagen opst\u00e5r, fordi der for hver indkommende 16-byte PING-pakke allokeres en 256-byte buffer til at danne et svar, men denne buffer frigives kun efter afslutning af n\u00f8gleforhandling. Som en midlertidig beskyttelse foresl\u00e5s det at indstille begr\u00e6nsninger ved hj\u00e6lp af direktiverne LoginGraceTime, MaxStartups og 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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Kilde: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"