{"id":112410,"date":"2023-12-22T03:10:14","date_gmt":"2023-12-22T01:10:16","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/smtp-smuggling-novaya-tehnika-spufinga-pochtovyh-soobshhenij"},"modified":"2023-12-22T03:10:14","modified_gmt":"2023-12-22T01:10:16","slug":"smtp-smuggling-novaya-tehnika-spufinga-pochtovyh-soobshhenij","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pt\/blog\/news\/smtp-smuggling-novaya-tehnika-spufinga-pochtovyh-soobshhenij","title":{"rendered":"SMTP Smuggling \u2014 uma nova t\u00e9cnica de spoofing de mensagens de email","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Pesquisadores da SEC Consult publicaram uma nova t\u00e9cnica de spoofing, resultante de diverg\u00eancias na conformidade com a especifica\u00e7\u00e3o em v\u00e1rias implementa\u00e7\u00f5es do protocolo SMTP. A t\u00e9cnica de ataque proposta permite dividir uma \u00fanica mensagem em v\u00e1rias diferentes durante a sua transmiss\u00e3o de um servidor SMTP de origem para outro servidor SMTP, que interpreta de maneira diferente a sequ\u00eancia para separa\u00e7\u00e3o de e-mails transmitidos atrav\u00e9s de uma \u00fanica conex\u00e3o. O m\u00e9todo pode ser utilizado para enviar e-mails falsos em nome de outros remetentes em servi\u00e7os de e-mail que verificam o remetente original. <\/p>\n

O problema \u00e9 causado pelo fato de que diferentes servidores SMTP interpretam de maneira diferente a sequ\u00eancia de t\u00e9rmino dos dados, o que pode levar \u00e0 divis\u00e3o de um e-mail em v\u00e1rios durante uma \u00fanica sess\u00e3o com o servidor SMTP. Na especifica\u00e7\u00e3o para marcar o final da transmiss\u00e3o de um e-mail, a sequ\u00eancia definida \u00e9 «\r\n.\r\n» (um ponto cercado pelos caracteres de retorno de carro e nova linha). Ap\u00f3s essa sequ\u00eancia, podem seguir comandos para transmitir outro e-mail sem desconectar. Alguns servidores SMTP seguem rigorosamente a especifica\u00e7\u00e3o, mas outros, para garantir a compatibilidade com alguns clientes de e-mail raros, tratam como delimitadores sequ\u00eancias como «\n.\n», «\n.\r\n», «\r\n.\n», «\r.\r», «\r\n0.\r\n» e «\r\n0.\r\n». <\/p>\n

O ataque consiste em que, para a primeira servidor<\/a>, que processa apenas o delimitador «\r\n.\r\n», envia um e-mail cujo corpo cont\u00e9m um delimitador alternativo, como «\r.\r», seguido por comandos para enviar a segunda mensagem. Como o primeiro servidor segue a especifica\u00e7\u00e3o rigorosamente, ele processa a sequ\u00eancia recebida como um \u00fanico e-mail. Se em seguida o e-mail for enviado para um servidor de tr\u00e2nsito ou para o servidor do destinat\u00e1rio, que tamb\u00e9m interpreta a sequ\u00eancia «\r.\r» como delimitador, ele ser\u00e1 processado como dois e-mails enviados separadamente (o segundo e-mail pode ser enviado em nome de um usu\u00e1rio que n\u00e3o est\u00e1 autenticado via «AUTH LOGIN», mas parecer\u00e1 correto para o destinat\u00e1rio).

\"SMTP<\/center>
\"SMTP<\/center> <\/p>\n

Como exemplos de servidores e servi\u00e7os SMTP que permitem delimitadores alternativos, podemos citar Postfix, Sendmail, MS Exchange Online e Cisco Secure Email Gateway, enquanto entre os servi\u00e7os de e-mail que n\u00e3o filtram delimitadores incorretos de e-mails ao se conectar a outros servidores est\u00e3o GMX, iCloud e Microsoft Outlook. <\/p>\n

Para bloquear o problema no Postfix nas vers\u00f5es 3.8.1, 3.7.6, 3.6.10 e 3.5.20, foi adicionada a configura\u00e7\u00e3o «smtpd_forbid_unauth_pipelining», que provoca a desconex\u00e3o em caso de uso de delimitadores que n\u00e3o atendem aos requisitos do RFC 2920 e RFC 5321. Atualmente, essa configura\u00e7\u00e3o est\u00e1 desativada por padr\u00e3o, mas planejam ativ\u00e1-la por padr\u00e3o na ramifica\u00e7\u00e3o Postfix 3.9, que est\u00e1 prevista para a primavera de 2024. Na ramifica\u00e7\u00e3o 3.9, tamb\u00e9m ser\u00e1 inclu\u00edda a configura\u00e7\u00e3o smtpd_forbid_bare_newline, que gera um erro ao usar apenas o caractere de nova linha («\n») para separar linhas, o que viola o RFC 5321. <\/p>\n

Na pr\u00f3xima vers\u00e3o do Sendmail 8.18.0.2, para prote\u00e7\u00e3o contra um ataque, na srv_features, foi proposta a op\u00e7\u00e3o ‘o’, que inclui o processamento apenas da sequ\u00eancia «\r\n.\r\n». Observa-se que desativar o suporte a delimitadores alternativos pode afetar a opera\u00e7\u00e3o de alguns clientes de e-mail raros que n\u00e3o est\u00e3o completamente em conformidade com a especifica\u00e7\u00e3o SMTP.
\n
Fonte: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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