{"id":87197,"date":"2020-07-05T07:42:02","date_gmt":"2020-07-05T05:42:02","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimost-v-ssh-klientah-openssh-i-putty"},"modified":"2020-07-05T07:42:02","modified_gmt":"2020-07-05T05:42:02","slug":"uyazvimost-v-ssh-klientah-openssh-i-putty","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pt\/blog\/news\/uyazvimost-v-ssh-klientah-openssh-i-putty","title":{"rendered":"Vulnerabilidade em clientes SSH OpenSSH e PuTTY","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Nos clientes SSH OpenSSH e PuTTY foi identificada<\/a><\/noindex> uma vulnerabilidade<\/a><\/noindex> (CVE-2020-14002<\/a><\/noindex> no PuTTY e CVE-2020-14145<\/a><\/noindex> no OpenSSH), levando a uma vazamento de informa\u00e7\u00f5es no algoritmo de negocia\u00e7\u00e3o de conex\u00e3o. A vulnerabilidade permite que um atacante, capaz de interceptar o tr\u00e1fego do cliente (por exemplo, ao conectar-se a um usu\u00e1rio atrav\u00e9s de um ponto de acesso sem fio controlado pelo atacante), identifique a tentativa de conex\u00e3o inicial do cliente com o host, quando a chave do host ainda n\u00e3o est\u00e1 armazenada em cache pelo cliente. <\/p>\n

Sabendo que o cliente est\u00e1 tentando se conectar pela primeira vez e ainda n\u00e3o possui a chave do host, o atacante pode retransmitir a conex\u00e3o atrav\u00e9s de si mesmo (MITM) e fornecer ao cliente sua chave de host, que o cliente SSH considerar\u00e1 a chave do host alvo, a menos que a verifica\u00e7\u00e3o da impress\u00e3o digital da chave seja realizada. Assim, o atacante pode organizar um MITM sem levantar suspeitas do usu\u00e1rio e ignorar sess\u00f5es em que o cliente j\u00e1 possui chaves de host em cache, cuja tentativa de substitui\u00e7\u00e3o resultaria em um alerta sobre a altera\u00e7\u00e3o da chave do host. O ataque se baseia na neglig\u00eancia dos usu\u00e1rios, que n\u00e3o realizam a verifica\u00e7\u00e3o manual da impress\u00e3o digital da chave do host na primeira conex\u00e3o. Aqueles que verificam as impress\u00f5es digitais das chaves est\u00e3o protegidos contra esses ataques.<\/p>\n

Como um sinal para determinar a primeira tentativa de conex\u00e3o, \u00e9 utilizada a altera\u00e7\u00e3o na ordem de enumera\u00e7\u00e3o dos algoritmos de chave do host suportados. No caso de ser a primeira conex\u00e3o, o cliente envia a lista de algoritmos padr\u00e3o, e se a chave do host j\u00e1 estiver em cache, o algoritmo associado a ela \u00e9 colocado em primeiro lugar (os algoritmos s\u00e3o classificados por ordem de prefer\u00eancia). <\/p>\n

O problema se manifesta em vers\u00f5es do OpenSSH de 5.7 a 8.3 e no PuTTY de 0.68 a 0.73. O problema no lan\u00e7amento<\/a><\/noindex> Lan\u00e7amento do Chrome OS 78 com suporte para desktops virtuais PuTTY 0.74<\/a><\/noindex> atrav\u00e9s da adi\u00e7\u00e3o de uma op\u00e7\u00e3o para desativar a constru\u00e7\u00e3o din\u00e2mica da lista de algoritmos de processamento de chaves do host em favor da enumera\u00e7\u00e3o dos algoritmos em uma ordem fixa.<\/p>\n

O projeto OpenSSH n\u00e3o pretende alterar o comportamento do cliente SSH, pois, se n\u00e3o for especificado o algoritmo da chave existente primeiro, haver\u00e1 uma tentativa de aplicar um algoritmo n\u00e3o correspondente \u00e0 chave em cache, resultando em um aviso sobre uma chave desconhecida. Ou seja, surge a escolha \u2014 ou a vazamento de informa\u00e7\u00f5es (OpenSSH e PuTTY), ou a emiss\u00e3o de avisos sobre a mudan\u00e7a de chave (Dropbear SSH) caso a chave salva n\u00e3o corresponda ao primeiro algoritmo da lista padr\u00e3o.<\/p>\n

Para garantir a prote\u00e7\u00e3o no OpenSSH, recomenda-se usar m\u00e9todos alternativos de verifica\u00e7\u00e3o da chave do host atrav\u00e9s de registros SSHFP no DNSSEC e certificados de host (PKI). Tamb\u00e9m \u00e9 poss\u00edvel desativar a sele\u00e7\u00e3o adaptativa de algoritmos de chaves de host por meio da op\u00e7\u00e3o HostKeyAlgorithms e usar a op\u00e7\u00e3o UpdateHostKeys para que o cliente obtenha chaves de host adicionais ap\u00f3s a autentica\u00e7\u00e3o.<\/p>\n

<\/a><\/noindex><\/p>\n

Fonte: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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