Foi disponibilizada uma vers\u00e3o corretiva do OpenSSH 9.9p2, que resolve duas vulnerabilidades identificadas pela Qualys. Foi demonstrado um exemplo de como essas vulnerabilidades podem ser usadas para realizar um ataque MITM, permitindo que, ao tentar conectar um cliente ao servidor SSH, o tr\u00e1fego seja redirecionado para um servidor falso, contornando a verifica\u00e7\u00e3o das chaves do host e criando para o cliente a apar\u00eancia de estar conectado ao servidor desejado (o cliente SSH aceitar\u00e1 a chave do host do servidor falso em vez da chave do servidor leg\u00edtimo). <\/p>\n
A primeira vulnerabilidade (CVE-2025-26465) \u00e9 causada por um erro l\u00f3gico no utilit\u00e1rio ssh, que permite contornar a verifica\u00e7\u00e3o da identidade do servidor e realizar um ataque MITM. O problema se manifesta a partir da vers\u00e3o OpenSSH 6.8p1 (dezembro de 2014) em configura\u00e7\u00f5es com a op\u00e7\u00e3o VerifyHostKeyDNS ativada. Na instala\u00e7\u00e3o padr\u00e3o do OpenSSH, essa op\u00e7\u00e3o est\u00e1 desativada por padr\u00e3o, mas foi ativada nas configura\u00e7\u00f5es do ssh no FreeBSD at\u00e9 mar\u00e7o de 2023. <\/p>\n
O problema \u00e9 que, no c\u00f3digo da fun\u00e7\u00e3o verify_host_key_callback(), ao chamar a fun\u00e7\u00e3o verify_host_key(), \u00e9 verificado apenas o c\u00f3digo de erro «-1», enquanto outros c\u00f3digos, como «-2», s\u00e3o ignorados. Como resultado, a fun\u00e7\u00e3o verify_host_key_callback() pode retornar um c\u00f3digo de sucesso «0», apesar de a fun\u00e7\u00e3o verify_host_key() ter retornado um erro «-2». O c\u00f3digo de erro «-2» \u00e9 retornado pela fun\u00e7\u00e3o verify_host_key() quando h\u00e1 falta de mem\u00f3ria. Se forem criadas condi\u00e7\u00f5es que impe\u00e7am a aloca\u00e7\u00e3o de mem\u00f3ria na fun\u00e7\u00e3o verify_host_key(), o SSH acreditar\u00e1 que a chave do host foi verificada com sucesso. Para criar tais condi\u00e7\u00f5es, um servidor SSH de ataque, para o qual o cliente \u00e9 redirecionado, retorna uma chave do host do tamanho m\u00e1ximo poss\u00edvel (256KB), e simultaneamente explora uma vazamento de mem\u00f3ria do lado do cliente SSH. <\/p>\n
As condi\u00e7\u00f5es para criar o vazamento de mem\u00f3ria s\u00e3o atingidas devido \u00e0 segunda vulnerabilidade (CVE-2025-26466), que afeta tanto o cliente ssh quanto servidor<\/a> sshd, e explorado sem autentica\u00e7\u00e3o. A vulnerabilidade permite esgotar a mem\u00f3ria dispon\u00edvel do processo e criar uma alta carga no CPU enviando um grande n\u00famero de pacotes SSH2_MSG_PING. No manipulador de pacotes SSH2_MSG_PING, h\u00e1 um vazamento de mem\u00f3ria que se manifesta a partir do lan\u00e7amento do OpenSSH 9.5p1 (agosto de 2023). O vazamento ocorre porque um buffer de 256 bytes \u00e9 alocado para cada pacote PING de 16 bytes recebido para formar uma resposta, mas esse buffer \u00e9 liberado apenas ap\u00f3s a conclus\u00e3o da negocia\u00e7\u00e3o de chaves. Como uma medida de prote\u00e7\u00e3o alternativa, recomenda-se configurar limites usando as diretivas LoginGraceTime, MaxStartups e 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 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Fonte: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"