{"id":37876,"date":"2019-10-31T22:20:17","date_gmt":"2019-10-31T19:20:17","guid":{"rendered":"https:\/\/prohoster.info\/blog\/raskryty-podrobnosti-kriticheskoj-uyazvimosti-v-exim\/"},"modified":"2019-10-31T22:20:17","modified_gmt":"2019-10-31T19:20:17","slug":"raskryty-podrobnosti-kriticheskoj-uyazvimosti-v-exim","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pt\/blog\/news\/raskryty-podrobnosti-kriticheskoj-uyazvimosti-v-exim","title":{"rendered":"Detalhes da vulnerabilidade cr\u00edtica no Exim foram revelados","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Publicado<\/a><\/noindex> release corretivo Exim 4.92.2<\/a><\/noindex> com corre\u00e7\u00e3o cr\u00edtica no aplicativo para Windows, que permitia ao usu\u00e1rio elevar seus privil\u00e9gios no sistema para administrador (a vulnerabilidade foi causada pela intera\u00e7\u00e3o inadequada entre o cliente GUI sem privil\u00e9gios e o servi\u00e7o de sistema).<\/a><\/noindex> (CVE-2019-15846<\/a><\/noindex>), que na configura\u00e7\u00e3o padr\u00e3o pode levar \u00e0 execu\u00e7\u00e3o remota de c\u00f3digo por um invasor com privil\u00e9gios de root. O problema ocorre apenas quando o suporte a TLS est\u00e1 ativado e \u00e9 explorado atrav\u00e9s da transmiss\u00e3o de um certificado de cliente especificamente formatado ou um valor modificado no SNI. A vulnerabilidade foi identificada<\/a><\/noindex> foi descoberto pela empresa Qualys.<\/p>\n

O problema est\u00e3o presentes<\/a><\/noindex> est\u00e1 no manipulador de escape de caracteres especiais em uma string (string_interpret_escape()<\/a><\/noindex> do string.c) e \u00e9 causada pelo fato de que o s\u00edmbolo \u2018\u2019 no final da string \u00e9 interpretado antes do caractere nulo (\u2018\u2019) e o escapa. Ao escapar, a sequ\u00eancia \u2018\u2019 e o subsequente c\u00f3digo nulo de final de string s\u00e3o tratados como um \u00fanico caractere e o ponteiro \u00e9 deslocado para os dados al\u00e9m da string, que s\u00e3o tratados como sua continua\u00e7\u00e3o. <\/p>\n

O c\u00f3digo que chama string_interpret_escape() aloca um buffer para a entrada, com base no tamanho real, e o ponteiro atribu\u00eddo acaba na \u00e1rea fora dos limites do buffer. Assim, ao tentar processar a string de entrada, ocorre uma leitura de dados da \u00e1rea fora da mem\u00f3ria alocada, e a tentativa de grava\u00e7\u00e3o da string desencriptada pode levar a uma grava\u00e7\u00e3o al\u00e9m do limite do buffer.<\/p>\n

Na configura\u00e7\u00e3o padr\u00e3o, a vulnerabilidade pode ser explorada atrav\u00e9s da transmiss\u00e3o de dados especificamente formatados no SNI ao estabelecer uma conex\u00e3o segura com o servidor. O problema tamb\u00e9m pode ser explorado atrav\u00e9s da modifica\u00e7\u00e3o dos valores peerdn em configura\u00e7\u00f5es que s\u00e3o ajustadas para autentica\u00e7\u00e3o por certificado de cliente ou ao importar certificados. O ataque por meio de SNI e peerdn \u00e9 poss\u00edvel desde a vers\u00e3o Exim 4.80<\/a><\/noindex>, na qual a fun\u00e7\u00e3o string_unprinting() foi aplicada para desemaranhar o conte\u00fado de peerdn e SNI.<\/p>\n

Um prot\u00f3tipo de exploit para ataque via SNI foi preparado, funcionando em arquiteturas i386 e amd64 em sistemas Linux com Glibc. O exploit utiliza sobreposi\u00e7\u00e3o de dados na \u00e1rea de heap, resultando na regrava\u00e7\u00e3o da mem\u00f3ria onde o nome do arquivo de log \u00e9 armazenado. O nome do arquivo \u00e9 substitu\u00eddo por \u2018\/....\/....\/....\/....\/....\/....\/....\/....\/etc\/passwd\u2019. Em seguida, a vari\u00e1vel com o endere\u00e7o do remetente, que \u00e9 o primeiro a ser salvo no log, \u00e9 regravada, permitindo a adi\u00e7\u00e3o de um novo usu\u00e1rio ao sistema. <\/p>\n

Atualiza\u00e7\u00f5es de pacotes para corre\u00e7\u00e3o de vulnerabilidades foram lan\u00e7adas pelos distribui\u00e7\u00f5es Debian<\/a><\/noindex>, Ubuntu<\/a><\/noindex>, Fedora<\/a><\/noindex>, SUSE\/openSUSE<\/a><\/noindex> e FreeBSD<\/a><\/noindex>. RHEL e CentOS para o problema n\u00e3o est\u00e3o afetados<\/a><\/noindex>, j\u00e1 que o Exim n\u00e3o faz parte do seu reposit\u00f3rio padr\u00e3o de pacotes (em EPEL<\/a><\/noindex> atualiza\u00e7\u00e3o j\u00e1<\/a><\/noindex> para smartphones OnePlus One, Fairphone 2, Nexus 4, Nexus 5, Nexus 7 2013, Meizu MX4\/PRO 5, Bq Aquaris E5\/E4.5\/M10. O projeto tamb\u00e9m<\/a><\/noindex>, mas ainda n\u00e3o foi colocado<\/a><\/noindex> no reposit\u00f3rio p\u00fablico). No c\u00f3digo do Exim, o problema \u00e9 resolvido por um patch de uma linha , desativando a a\u00e7\u00e3o de escape da barra invertida, se estiver no final da linha.<\/a><\/noindex>Como uma solu\u00e7\u00e3o alternativa para bloquear a vulnerabilidade, pode-se desativar o suporte a TLS ou adicionar na<\/p>\n

se\u00e7\u00e3o ACL \u00abacl_smtp_mail\u00bb:
\nse\u00e7\u00e3o ACL \u2018acl_smtp_mail\u2019:\n<\/p>\n

deny condition = ${if eq{}{${substr{-1}{1}{$tls_in_sni}}}}
\n deny condition = ${if eq{}{${substr{-1}{1}{$tls_in_peerdn}}}}<\/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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[…]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-37876","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Detalhes sobre a vulnerabilidade cr\u00edtica no Exim | ProHoster","description":"\ud83e\udd47Detalhes sobre uma vulnerabilidade cr\u00edtica no Exim foram revelados | 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