Ap\u00f3s a vulnerabilidade identificada no final de janeiro, que permitia o acesso como usu\u00e1rio root sem verificar a senha, foram descobertos v\u00e1rios m\u00e9todos de eleva\u00e7\u00e3o de privil\u00e9gios no servidor telnetd do pacote GNU InetUtils, decorrentes da remo\u00e7\u00e3o incompleta da vulnerabilidade em 1999 (CVE-1999-0073). <\/p>\n
As vulnerabilidades s\u00e3o causadas pela capacidade do telnetd de permitir que o cliente envie vari\u00e1veis de ambiente para o servidor atrav\u00e9s da op\u00e7\u00e3o ENVIRON. Tais vari\u00e1veis de ambiente s\u00e3o configuradas e processadas no contexto do processo telnetd e s\u00e3o passadas para os processos filhos que ele inicia, incluindo o processo \/bin\/login executado com privil\u00e9gios de root. A vulnerabilidade CVE-1999-0073 permitia que o cliente telnet enviasse a vari\u00e1vel de ambiente LD_LIBRARY_PATH, cuja configura\u00e7\u00e3o leva ao carregamento da biblioteca compartilhada especificada pelo usu\u00e1rio ao iniciar o processo login. Quando h\u00e1 possibilidade de carregar arquivos em um sistema que suporta conex\u00f5es via protocolo telnet, o atacante pode carregar uma biblioteca especialmente formatada e for\u00e7ar seu carregamento com privil\u00e9gios de root. <\/p>\n
No pacote telnetd do GNU InetUtils, uma vulnerabilidade foi corrigida ao proibir vari\u00e1veis de ambiente perigosas atrav\u00e9s da filtragem por m\u00e1scaras \u2018LD_\u2019, \u2018LIBPATH\u2019, \u2018ENV\u2019, \u2018IFS\u2019 e \u2018_RLD_\u2019. No entanto, a vari\u00e1vel de ambiente \u2018CREDENTIALS_DIRECTORY\u2019 n\u00e3o foi bloqueada, sendo processada ao iniciar \/usr\/bin\/login. Com essa vari\u00e1vel, o usu\u00e1rio poderia alterar o diret\u00f3rio de configura\u00e7\u00f5es de credenciais e colocar no novo diret\u00f3rio um arquivo login.noauth com o valor 'yes', que ativa o login sem senha (equivalente a passar a flag \u2018-f\u2019 para o processo login). Esta configura\u00e7\u00e3o se aplica a todos os usu\u00e1rios, incluindo o root. <\/p>\n
O ataque consiste na cria\u00e7\u00e3o, por um usu\u00e1rio n\u00e3o privilegiado, de um subdiret\u00f3rio em seu diret\u00f3rio home, carregando nele o arquivo login.noauth e tentando o login com a vari\u00e1vel de ambiente \u2018CREDENTIALS_DIRECTORY=diret\u00f3rio criado\u2019 e passando a vari\u00e1vel de ambiente \u2018USER=root\u2019 (o telnet possui um modo de conex\u00e3o autom\u00e1tica, onde o nome do usu\u00e1rio \u00e9 obtido n\u00e3o da linha de comando, mas passado atrav\u00e9s da vari\u00e1vel de ambiente USER). Exemplo de exploit. <\/p>\n
Foi identificado mais um m\u00e9todo de obten\u00e7\u00e3o de acesso root atrav\u00e9s do telnetd, relacionado \u00e0 manipula\u00e7\u00e3o das vari\u00e1veis de ambiente OUTPUT_CHARSET e LANGUAGE, processadas pela biblioteca GNU gettext, e \u00e0 vari\u00e1vel de ambiente GCONV_PATH, utilizada na glibc. Ao definir as vari\u00e1veis de ambiente OUTPUT_CHARSET e LANGUAGE, o atacante pode ativar a funcionalidade de convers\u00e3o de codifica\u00e7\u00e3o de caracteres no gettext, chamando a fun\u00e7\u00e3o iconv_open(). Por sua vez, ao executar a fun\u00e7\u00e3o iconv_open() ao carregar o arquivo de configura\u00e7\u00e3o gconv-modules, o caminho \u00e9 calculado considerando a vari\u00e1vel de ambiente GCONV_PATH. Atrav\u00e9s da substitui\u00e7\u00e3o do arquivo gconv-modules, pode-se organizar o carregamento de uma biblioteca compartilhada pr\u00f3pria durante a sa\u00edda de uma string localizada pelo processo login. <\/p>\n
Os identificadores CVE para as vulnerabilidades marcadas ainda n\u00e3o foram atribu\u00eddos. Como m\u00e9todo de prote\u00e7\u00e3o, est\u00e1 sendo considerado o uso de uma lista branca de valores aceitos (\u2018TERM\u2019, \u2018DISPLAY\u2019, \u2018USER\u2019, \u2018LOGNAME\u2019 e \u2018POSIXLY_CORRECT\u2019) bloqueando todas as outras vari\u00e1veis de ambiente, similar ao que \u00e9 feito com vari\u00e1veis de ambiente no OpenSSH. As vulnerabilidades foram confirmadas no pacote GNU InetUtils. servidor<\/a> telnetd, que \u00e9 fornecido no Debian, Ubuntu e distribui\u00e7\u00f5es derivadas. At\u00e9 o momento, n\u00e3o h\u00e1 corre\u00e7\u00f5es para o GNU InetUtils. O Rocky Linux 9 fornece uma vers\u00e3o modificada do telnetd que n\u00e3o apresenta a vulnerabilidade, na qual, em vez de filtrar as vari\u00e1veis de ambiente perigosas, \u00e9 feita uma verifica\u00e7\u00e3o baseada em lista branca. A filtragem baseada em lista branca tamb\u00e9m \u00e9 implementada no telnetd do FreeBSD. No OpenBSD, o telnetd foi removido do sistema em 2005. \u0421\u043b\u0435\u0434\u043e\u043c \u0437\u0430 \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043d\u043e\u0439 \u0432 \u043a\u043e\u043d\u0446\u0435 \u044f\u043d\u0432\u0430\u0440\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c\u044e, \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u0432\u0448\u0435\u0439 \u043f\u043e\u0434\u043a\u043b\u044e\u0447\u0438\u0442\u044c\u0441\u044f \u043f\u043e\u0434 \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u043c root \u0431\u0435\u0437 \u043f\u0440\u043e\u0432\u0435\u0440\u043a\u0438 \u043f\u0430\u0440\u043e\u043b\u044f, \u0432 \u0441\u0435\u0440\u0432\u0435\u0440\u0435 telnetd \u0438\u0437 \u043d\u0430\u0431\u043e\u0440\u0430 GNU InetUtils \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043e \u043d\u0435\u0441\u043a\u043e\u043b\u044c\u043a\u043e \u0441\u043f\u043e\u0441\u043e\u0431\u043e\u0432 \u043f\u043e\u0432\u044b\u0448\u0435\u043d\u0438\u044f \u0441\u0432\u043e\u0438\u0445 \u043f\u0440\u0438\u0432\u0438\u043b\u0435\u0433\u0438\u0439, \u0441\u0442\u0430\u0432\u0448\u0438\u0445 \u0441\u043b\u0435\u0434\u0441\u0442\u0432\u0438\u0435\u043c \u043d\u0435\u043f\u043e\u043b\u043d\u043e\u0433\u043e \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u0438\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 \u0432 1999 \u0433\u043e\u0434\u0443 (CVE-1999-0073). \u0423\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 \u0432\u044b\u0437\u0432\u0430\u043d\u044b \u043d\u0430\u043b\u0438\u0447\u0438\u0435\u043c \u0432 telnetd \u0432\u043e\u0437\u043c\u043e\u0436\u043d\u043e\u0441\u0442\u0438 \u043f\u0435\u0440\u0435\u0434\u0430\u0447\u0438 \u043a\u043b\u0438\u0435\u043d\u0442\u043e\u043c \u043f\u0435\u0440\u0435\u043c\u0435\u043d\u043d\u044b\u0445 \u043e\u043a\u0440\u0443\u0436\u0435\u043d\u0438\u044f \u043d\u0430 \u0441\u0435\u0440\u0432\u0435\u0440 \u043f\u0440\u0438 \u043f\u043e\u043c\u043e\u0449\u0438 \u043e\u043f\u0446\u0438\u0438 ENVIRON. \u041f\u043e\u0434\u043e\u0431\u043d\u044b\u0435 \u043f\u0435\u0440\u0435\u043c\u0435\u043d\u043d\u044b\u0435 […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":8,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-162791","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\udd47Uma s\u00e9rie de novas vulnerabilidades no telnetd, permitindo a obten\u00e7\u00e3o de privil\u00e9gios root no sistema | ProHoster","description":"Ap\u00f3s a vulnerabilidade identificada no final de janeiro, que permitia a conex\u00e3o como usu\u00e1rio root sem 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Fonte: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"