{"id":87197,"date":"2020-07-05T07:42:02","date_gmt":"2020-07-05T05:42:02","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimost-v-ssh-klientah-openssh-i-putty"},"modified":"2020-07-05T07:42:02","modified_gmt":"2020-07-05T05:42:02","slug":"uyazvimost-v-ssh-klientah-openssh-i-putty","status":"publish","type":"post","link":"https:\/\/prohoster.info\/it\/blog\/novosti-interneta\/uyazvimost-v-ssh-klientah-openssh-i-putty","title":{"rendered":"Vulnerabilit\u00e0 nei client SSH OpenSSH e PuTTY","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Nei client SSH OpenSSH e PuTTY \u00e8 stata rilevata<\/a><\/noindex> una vulnerabilit\u00e0<\/a><\/noindex> (CVE-2020-14002<\/a><\/noindex> in PuTTY e CVE-2020-14145<\/a><\/noindex> in OpenSSH), che porta a una perdita di informazioni nell'algoritmo di negoziazione della connessione. Questa vulnerabilit\u00e0 consente a un attaccante, in grado di intercettare il traffico del client (ad esempio, nel caso di una connessione di un utente tramite un punto di accesso wireless controllato dall'attaccante), di determinare il tentativo di connessione iniziale del client a un host, mentre la chiave host non \u00e8 ancora stata memorizzata nella cache dal client. <\/p>\n

Sapendo che il cliente sta cercando di connettersi per la prima volta e non ha ancora una chiave host dalla propria parte, un attaccante pu\u00f2 trasmettere la connessione attraverso di s\u00e9 (MITM) e fornire al cliente la propria chiave host, che il client SSH considerer\u00e0 la chiave dell'host di destinazione, se non esegue la verifica dell'impronta della chiave. In questo modo, l'attaccante pu\u00f2 orchestrare un attacco MITM senza suscitare sospetti nell'utente e ignorare le sessioni in cui il client ha gi\u00e0 chiavi host memorizzate in cache, il cui tentativo di sostituzione comporterebbe un avviso sul cambiamento della chiave host. L'attacco si basa sulla distrazione degli utenti che non eseguono la verifica manuale dell'impronta della chiave host al primo collegamento. Coloro che controllano le impronte delle chiavi sono protetti da tali attacchi.<\/p>\n

Un segno per identificare il primo tentativo di connessione \u00e8 la modifica dell'ordine di elencazione degli algoritmi di chiavi host supportati. In caso di prima connessione, il client trasmette un elenco di algoritmi predefiniti, mentre se la chiave host \u00e8 gi\u00e0 presente nella cache, l'algoritmo associato viene posto al primo posto (gli algoritmi vengono ordinati in base alla preferenza). <\/p>\n

Il problema si manifesta nelle versioni di OpenSSH dalla 5.7 all'8.3 e in PuTTY dalla 0.68 alla 0.73. Il problema risolto<\/a><\/noindex> in rilascio PuTTY 0.74<\/a><\/noindex> attraverso l'aggiunta di un'opzione per disabilitare la costruzione dinamica dell'elenco degli algoritmi di gestione delle chiavi host a favore di un'elencazione degli algoritmi in ordine fisso.<\/p>\n

Il progetto OpenSSH non prevede di modificare il comportamento del client SSH, poich\u00e9 se non si specifica l'algoritmo della chiave esistente per primo, verr\u00e0 tentato di applicare un algoritmo non corrispondente alla chiave memorizzata, con un avviso riguardo una chiave sconosciuta. In altre parole, si presenta una scelta: o una fuga di informazioni (OpenSSH e PuTTY), oppure l'emissione di avvisi sulla modifica della chiave (Dropbear SSH) nel caso in cui la chiave salvata non corrisponda al primo algoritmo nell'elenco predefinito.<\/p>\n

Per garantire la sicurezza in OpenSSH, si propone di utilizzare metodi alternativi per la verifica della chiave host tramite record SSHFP in DNSSEC e certificati host (PKI). \u00c8 anche possibile disabilitare la selezione adattiva degli algoritmi delle chiavi host tramite l'opzione HostKeyAlgorithms e utilizzare l'opzione UpdateHostKeys per ottenere chiavi host aggiuntive da parte del client dopo l'autenticazione.<\/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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Questa vulnerabilit\u00e0 consente a un attaccante, in grado di intercettare il traffico del client (ad esempio, quando un utente si connette tramite un punto di accesso wireless controllato dall'attaccante), di identificare il tentativo di connessione iniziale del client all'host, quando la chiave dell'host non \u00e8 ancora stata memorizzata nella cache dal client. Sapendo che","canonical_url":"https:\/\/prohoster.info\/it\/blog\/novosti-interneta\/uyazvimost-v-ssh-klientah-openssh-i-putty","robots":"max-image-preview:large","keywords":"","webmasterTools":{"miscellaneous":""},"schema":null,"og:locale":"it_IT","og:site_name":"ProHoster | \u041a\u0443\u043f\u0438\u0442\u044c \u043d\u0430\u0434\u0435\u0436\u043d\u044b\u0439 \u0445\u043e\u0441\u0442\u0438\u043d\u0433 \u0434\u043b\u044f \u0441\u0430\u0439\u0442\u043e\u0432 \u0441 \u0437\u0430\u0449\u0438\u0442\u043e\u0439 \u043e\u0442 DDoS, VPS VDS \u0441\u0435\u0440\u0432\u0435\u0440\u044b","og:type":"article","og:title":"\ud83e\udd47\u0423\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c \u0432 SSH-\u043a\u043b\u0438\u0435\u043d\u0442\u0430\u0445 OpenSSH \u0438 PuTTY | ProHoster","og:description":"\u0412 SSH-\u043a\u043b\u0438\u0435\u043d\u0442\u0430\u0445 OpenSSH \u0438 PuTTY \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c 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