Um conjunto de patches foi publicado para corrigir 6 vulnerabilidades no carregador GRUB2, a maioria das quais leva a acessos \u00e0 mem\u00f3ria ap\u00f3s sua libera\u00e7\u00e3o (use-after-free). As quest\u00f5es potencialmente identificadas podem ser exploradas para contornar o mecanismo de inicializa\u00e7\u00e3o verificada UEFI Secure Boot. O status da corre\u00e7\u00e3o das vulnerabilidades nas distribui\u00e7\u00f5es pode ser avaliado nas seguintes p\u00e1ginas: Debian, Ubuntu, SUSE, RHEL, Arch e Fedora. Para corrigir os problemas no GRUB2, n\u00e3o \u00e9 suficiente apenas atualizar o pacote; tamb\u00e9m \u00e9 necess\u00e1rio gerar novas assinaturas digitais internas e atualizar instaladores, carregadores, pacotes de kernel, firmwares fwupd e a camada shim. <\/p>\n
Vulnerabilidades identificadas: <\/p>\n
Na maioria das distribui\u00e7\u00f5es Linux, para a inicializa\u00e7\u00e3o verificada no modo UEFI Secure Boot, \u00e9 usada uma pequena camada shim, assinada digitalmente pela Microsoft. Essa camada verifica o GRUB2 com seu pr\u00f3prio certificado, permitindo que os desenvolvedores das distribui\u00e7\u00f5es n\u00e3o precisem assinar cada atualiza\u00e7\u00e3o do kernel e do GRUB pela Microsoft. Vulnerabilidades no GRUB2 permitem a execu\u00e7\u00e3o de c\u00f3digo ap\u00f3s a verifica\u00e7\u00e3o bem-sucedida do shim, mas antes da inicializa\u00e7\u00e3o do sistema operacional, infiltrando-se na cadeia de confian\u00e7a com o modo Secure Boot ativo e obtendo controle total sobre o processo de inicializa\u00e7\u00e3o, por exemplo, para inicializar outro SO, modificar componentes do sistema operacional e contornar a prote\u00e7\u00e3o Lockdown. <\/p>\n
Para bloquear a vulnerabilidade sem revogar a assinatura digital, as distribui\u00e7\u00f5es podem usar o mecanismo SBAT (UEFI Secure Boot Advanced Targeting), cujo suporte \u00e9 implementado para GRUB2, shim e fwupd na maioria das distribui\u00e7\u00f5es populares do Linux. O SBAT foi desenvolvido em conjunto com a Microsoft e implica a adi\u00e7\u00e3o de metadados adicionais nos arquivos execut\u00e1veis dos componentes UEFI, que incluem informa\u00e7\u00f5es sobre o fabricante, produto, componente e vers\u00e3o. Esses metadados s\u00e3o assinados digitalmente e podem ser inclu\u00eddos separadamente nas listas de componentes permitidos ou bloqueados para o UEFI Secure Boot. <\/p>\n
O SBAT permite bloquear o uso de assinaturas digitais para vers\u00f5es espec\u00edficas de componentes sem a necessidade de revogar chaves para o Secure Boot. O bloqueio de vulnerabilidades via SBAT n\u00e3o requer o uso da lista de certificados revogados UEFI (dbx), sendo realizado no n\u00edvel de substitui\u00e7\u00e3o de chaves internas para a forma\u00e7\u00e3o de assinaturas e atualiza\u00e7\u00e3o do GRUB2, shim e outros artefatos de inicializa\u00e7\u00e3o fornecidos pelas distribui\u00e7\u00f5es. Antes da implementa\u00e7\u00e3o do SBAT, a atualiza\u00e7\u00e3o da lista de certificados revogados (dbx, UEFI Revocation List) era uma condi\u00e7\u00e3o obrigat\u00f3ria para o bloqueio total da vulnerabilidade, pois um atacante, independentemente do sistema operacional utilizado, podia comprometer o UEFI Secure Boot usando um meio de inicializa\u00e7\u00e3o com uma vers\u00e3o antiga vulner\u00e1vel do GRUB2, assinada digitalmente. \u041e\u043f\u0443\u0431\u043b\u0438\u043a\u043e\u0432\u0430\u043d \u043d\u0430\u0431\u043e\u0440 \u043f\u0430\u0442\u0447\u0435\u0439 \u0441 \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u0438\u0435\u043c 6 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0435\u0439 \u0432 \u0437\u0430\u0433\u0440\u0443\u0437\u0447\u0438\u043a\u0435 GRUB2, \u0431\u043e\u043b\u044c\u0448\u0438\u043d\u0441\u0442\u0432\u043e \u0438\u0437 \u043a\u043e\u0442\u043e\u0440\u044b\u0445 \u043f\u0440\u0438\u0432\u043e\u0434\u0438\u0442 \u043a \u043e\u0431\u0440\u0430\u0449\u0435\u043d\u0438\u044e \u043a \u043f\u0430\u043c\u044f\u0442\u0438 \u043f\u043e\u0441\u043b\u0435 \u0435\u0451 \u043e\u0441\u0432\u043e\u0431\u043e\u0436\u0434\u0435\u043d\u0438\u044f (use-after-free). \u041f\u043e\u0442\u0435\u043d\u0446\u0438\u0430\u043b\u044c\u043d\u043e \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043d\u044b\u0435 \u043f\u0440\u043e\u0431\u043b\u0435\u043c\u044b \u043c\u043e\u0433\u0443\u0442 \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u044c\u0441\u044f \u0434\u043b\u044f \u043e\u0431\u0445\u043e\u0434\u0430 \u043c\u0435\u0445\u0430\u043d\u0438\u0437\u043c\u0430 \u0432\u0435\u0440\u0438\u0444\u0438\u0446\u0438\u0440\u043e\u0432\u0430\u043d\u043d\u043e\u0439 \u0437\u0430\u0433\u0440\u0443\u0437\u043a\u0438 UEFI Secure Boot. \u0421\u0442\u0430\u0442\u0443\u0441 \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u0438\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0435\u0439 \u0432 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Fonte: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"