{"id":172668,"date":"2026-05-19T06:24:52","date_gmt":"2026-05-19T04:24:52","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/v-linux-zakryta-uyazvimost-ssh-keysign-pwn-pozvolyayushhaya-lokalnym-polzovatelyam-chitat-root-fajly"},"modified":"2026-05-19T12:52:18","modified_gmt":"2026-05-19T10:52:18","slug":"v-linux-zakryta-uyazvimost-ssh-keysign-pwn-pozvolyayushhaya-lokalnym-polzovatelyam-chitat-root-fajly","status":"publish","type":"post","link":"https:\/\/prohoster.info\/pt\/blog\/news\/v-linux-zakryta-uyazvimost-ssh-keysign-pwn-pozvolyayushhaya-lokalnym-polzovatelyam-chitat-root-fajly","title":{"rendered":"No Linux, foi corrigida a vulnerabilidade ssh-keysign-pwn, permitindo que usu\u00e1rios locais leiam arquivos de root.","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>Uma vulnerabilidade no n\u00facleo do Linux foi corrigida, recebendo o nome n\u00e3o oficial <strong>ssh-keysign-pwn<\/strong>. O problema permite que um usu\u00e1rio local n\u00e3o privilegiado leia arquivos que devem estar dispon\u00edveis apenas para o root, incluindo chaves privadas de host SSH e, em alguns cen\u00e1rios, \/etc\/shadow. No momento da publica\u00e7\u00e3o, um CVE separado para o problema ainda n\u00e3o havia sido atribu\u00eddo.<\/p>\n<p>  <noindex><noindex><\/p>\n<p>Apesar do nome, n\u00e3o se trata de um erro no OpenSSH como servidor de rede sshd, mas sim de um <a rel=\"nofollow\" href=\"https:\/\/github.com\/torvalds\/linux\/commit\/31e62c2ebbfdc3fe3dbdf5e02c92a9dc67087a3a\">defeito<\/a> na l\u00f3gica do n\u00facleo do Linux, relacionado \u00e0s verifica\u00e7\u00f5es de ptrace e acesso a descritores de arquivo de outro processo atrav\u00e9s de pidfd_getfd(2). A utilidade OpenSSH ssh-keysign surgiu como um dos exemplos convenientes de explora\u00e7\u00e3o, pois trabalha com chaves privadas de host, que geralmente pertencem ao root e n\u00e3o est\u00e3o dispon\u00edveis para usu\u00e1rios comuns.<\/p>\n<p><\/noindex><\/noindex> <noindex><\/p>\n<p><a rel=\"nofollow\" href=\"https:\/\/github.com\/0xdeadbeefnetwork\/ssh-keysign-pwn\">A ess\u00eancia do erro<\/a> \u00e9 que a fun\u00e7\u00e3o __ptrace_may_access() tratava incorretamente o estado de um processo cuja estrutura de mem\u00f3ria mm j\u00e1 havia desaparecido, mas ainda havia descritores de arquivo abertos. Durante a finaliza\u00e7\u00e3o do processo, o n\u00facleo chama exit_mm() antes de fechar os arquivos atrav\u00e9s de exit_files(). Nesse curto intervalo, o processo j\u00e1 parece n\u00e3o ter um espa\u00e7o de endere\u00e7o de usu\u00e1rio comum, mas seus arquivos abertos ainda existem. Por causa disso, a verifica\u00e7\u00e3o do estado 'dumpable' poderia ser contornada, e pidfd_getfd() poderia acessar um descritor de arquivo de outro processo com UID correspondente.<\/p>\n<p><\/noindex> <\/p>\n<p>O cen\u00e1rio pr\u00e1tico gira em torno de programas setuid, que primeiro abrem um arquivo sens\u00edvel com privil\u00e9gios de root, depois descartam privil\u00e9gios e finalizam, ainda mantendo um descritor aberto. Na descri\u00e7\u00e3o publicada, como exemplo, \u00e9 mencionado o ssh-keysign: ele abre \/etc\/ssh\/ssh_host_{ecdsa,ed25519,rsa}_key, ap\u00f3s o que descarta os direitos e pode finalizar se EnableSSHKeysign estiver desativado. Essas chaves devem estar dispon\u00edveis apenas para o root, pois s\u00e3o usadas para autentica\u00e7\u00e3o baseada em host.<\/p>\n<p>Outro exemplo \u00e9 o chage, que pode abrir \/etc\/shadow, depois descartar direitos efetivos e finalizar. Como resultado, o ataque n\u00e3o necessariamente concede imediatamente um shell com privil\u00e9gios de root, mas permite acessar o conte\u00fado de arquivos que normalmente s\u00e3o considerados criticamente confidenciais. A revela\u00e7\u00e3o de \/etc\/shadow \u00e9 perigosa devido \u00e0 possibilidade de posterior ataque de for\u00e7a bruta offline, e a revela\u00e7\u00e3o de chaves privadas SSH de host representa o risco de falsifica\u00e7\u00e3o de host ou realiza\u00e7\u00e3o de ataques a scripts SSH confi\u00e1veis.<\/p>\n<p>A corre\u00e7\u00e3o j\u00e1 foi aceita no ramo principal do Linux. O commit 31e62c2ebbfd, com o t\u00edtulo ptrace: l\u00f3gica 'get_dumpable()' ligeiramente mais sensata, altera o comportamento da verifica\u00e7\u00e3o de dumpability: o n\u00facleo agora mant\u00e9m o estado user_dumpable quando mm desaparece e exige uma verifica\u00e7\u00e3o correta do CAP_SYS_PTRACE para contornar. O patch afeta include\/linux\/sched.h, kernel\/exit.c e kernel\/ptrace.c.<\/p>\n<p>A vulnerabilidade foi reportada pela Qualys e corrigida por Linus Torvalds em 14 de maio de 2026. O Phoronix observa que, no momento da publica\u00e7\u00e3o, o problema afetava todas as vers\u00f5es do n\u00facleo Linux at\u00e9 o estado atual da \u00e1rvore mainline antes da corre\u00e7\u00e3o. O autor do PoC tamb\u00e9m indica que s\u00e3o vulner\u00e1veis n\u00facleos anteriores ao commit 31e62c2ebbfd, incluindo ramos est\u00e1veis at\u00e9 14 de maio.<\/p>\n<p> <noindex><\/p>\n<p>\u00c9 importante ressaltar que, para a explora\u00e7\u00e3o, n\u00e3o \u00e9 necess\u00e1rio carregar m\u00f3dulos espec\u00edficos do n\u00facleo, como em v\u00e1rias vulnerabilidades recentes de LPE. \u00c9 suficiente ter acesso local n\u00e3o privilegiado ao sistema e um processo helper privilegiado adequado. O desenvolvedor do Debian, Daniel Baumann <a rel=\"nofollow\" href=\"https:\/\/blog.daniel-baumann.ch\/posts\/20260515-1.html\">observou<\/a>, que este problema deve ser resolvido com uma atualiza\u00e7\u00e3o do n\u00facleo e o posterior rein\u00edcio no n\u00facleo corrigido.<\/p>\n<p><\/noindex> <\/p>\n<p>No reposit\u00f3rio publicado com a demonstra\u00e7\u00e3o, foi afirmada a verifica\u00e7\u00e3o no Raspberry Pi OS Bookworm com n\u00facleo 6.12.75, Debian 13, Ubuntu 22.04, Ubuntu 24.04, Ubuntu 26.04, Arch e CentOS 9. Essa lista deve ser considerada como dados do autor do PoC, e n\u00e3o como uma lista exaustiva: como o erro reside na l\u00f3gica geral do n\u00facleo, a cobertura real depende da vers\u00e3o do n\u00facleo e da disponibilidade de corre\u00e7\u00f5es backport em distribui\u00e7\u00f5es espec\u00edficas.<\/p>\n<p>Para os administradores, a principal recomenda\u00e7\u00e3o \u00e9 simples: instalar o pacote de n\u00facleo atualizado de sua distribui\u00e7\u00e3o e reiniciar o sistema. Se houver raz\u00f5es para acreditar que j\u00e1 houve acesso local n\u00e3o privilegiado de um invasor na m\u00e1quina, ap\u00f3s a atualiza\u00e7\u00e3o, tamb\u00e9m \u00e9 aconselh\u00e1vel considerar a rota\u00e7\u00e3o das chaves host do SSH e verificar as contas em \/etc\/shadow, uma vez que a pr\u00f3pria vulnerabilidade est\u00e1 relacionada \u00e0 leitura de arquivos sens\u00edveis, e n\u00e3o apenas \u00e0 contornagem abstrata da verifica\u00e7\u00e3o de acesso.<\/p>\n<p>No Debian, j\u00e1 come\u00e7aram os trabalhos para a implementa\u00e7\u00e3o da corre\u00e7\u00e3o: Baumann informou sobre o cherry-pick do commit upstream nos trixie-fastforward-backports e o envio de um merge request para o Debian sid. No merge request, est\u00e1 claramente indicado que est\u00e1 sendo transferido o commit 31e62c2 para corrigir a l\u00f3gica de dumpability do ptrace, permitindo que um usu\u00e1rio n\u00e3o privilegiado leia arquivos root.<\/p>\n<p>Fonte: <a \ncontent=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/www.linux.org.ru\/news\/security\/18293396\">linux.org.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u0412 \u044f\u0434\u0440\u0435 Linux \u0438\u0441\u043f\u0440\u0430\u0432\u043b\u0435\u043d\u0430 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c, \u043f\u043e\u043b\u0443\u0447\u0438\u0432\u0448\u0430\u044f \u043d\u0435\u043e\u0444\u0438\u0446\u0438\u0430\u043b\u044c\u043d\u043e\u0435 \u043d\u0430\u0437\u0432\u0430\u043d\u0438\u0435 ssh-keysign-pwn. \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u0435\u0442 \u043b\u043e\u043a\u0430\u043b\u044c\u043d\u043e\u043c\u0443 \u043d\u0435\u043f\u0440\u0438\u0432\u0438\u043b\u0435\u0433\u0438\u0440\u043e\u0432\u0430\u043d\u043d\u043e\u043c\u0443 \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u044e \u0447\u0438\u0442\u0430\u0442\u044c \u0444\u0430\u0439\u043b\u044b, \u043a\u043e\u0442\u043e\u0440\u044b\u0435 \u0434\u043e\u043b\u0436\u043d\u044b \u0431\u044b\u0442\u044c \u0434\u043e\u0441\u0442\u0443\u043f\u043d\u044b \u0442\u043e\u043b\u044c\u043a\u043e root, \u0432\u043a\u043b\u044e\u0447\u0430\u044f \u043f\u0440\u0438\u0432\u0430\u0442\u043d\u044b\u0435 SSH host-\u043a\u043b\u044e\u0447\u0438 \u0438, \u0432 \u043e\u0442\u0434\u0435\u043b\u044c\u043d\u044b\u0445 \u0441\u0446\u0435\u043d\u0430\u0440\u0438\u044f\u0445, \/etc\/shadow. \u041d\u0430 \u043c\u043e\u043c\u0435\u043d\u0442 \u043f\u0443\u0431\u043b\u0438\u043a\u0430\u0446\u0438\u0438 \u043e\u0442\u0434\u0435\u043b\u044c\u043d\u044b\u0439 CVE \u0434\u043b\u044f \u043f\u0440\u043e\u0431\u043b\u0435\u043c\u044b \u0435\u0449\u0451 \u043d\u0435 \u0431\u044b\u043b \u043d\u0430\u0437\u043d\u0430\u0447\u0435\u043d. \u041d\u0435\u0441\u043c\u043e\u0442\u0440\u044f \u043d\u0430 \u043d\u0430\u0437\u0432\u0430\u043d\u0438\u0435, \u0440\u0435\u0447\u044c \u0438\u0434\u0451\u0442 \u043d\u0435 \u043e\u0431 \u043e\u0448\u0438\u0431\u043a\u0435 \u0432 OpenSSH \u043a\u0430\u043a \u0441\u0435\u0442\u0435\u0432\u043e\u043c \u0441\u0435\u0440\u0432\u0435\u0440\u0435 [&hellip;]<\/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-172668","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 5.0.3 - aioseo.com -->\n\t<meta name=\"description\" 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