{"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\/da\/blog\/news\/uyazvimost-v-ssh-klientah-openssh-i-putty","title":{"rendered":"S\u00e5rbarhed i SSH-klienter OpenSSH og PuTTY","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

I SSH-klienterne OpenSSH og PuTTY opdaget<\/a><\/noindex> ASLR i programmer med setuid-flaget og bestemme adressefordelingen i de indl\u00e6ste biblioteker gennem manipulation af milj\u00f8variablen LD_PREFER_MAP_32BIT_EXEC.<\/a><\/noindex> (CVE-2020-14002<\/a><\/noindex> i PuTTY og CVE-2020-14145<\/a><\/noindex> i OpenSSH), der f\u00f8rer til l\u00e6kage af information i forbindelse med forbindelsens forhandlingsalgoritme. S\u00e5rbarheden tillader en angriber, der er i stand til at opsnappe klientens trafik (for eksempel n\u00e5r en bruger tilslutter sig via et tr\u00e5dl\u00f8st adgangspunkt kontrolleret af angriberen), at identificere den oprindelige forbindelse, som klienten fors\u00f8ger at etablere til v\u00e6rten, n\u00e5r klienten endnu ikke har cachet v\u00e6rtsn\u00f8glen. <\/p>\n

Ved at vide, at klienten fors\u00f8ger at oprette forbindelse for f\u00f8rste gang og endnu ikke har v\u00e6rtsn\u00f8glen, kan angriberen lede forbindelsen gennem sig selv (MITM) og pr\u00e6sentere sin egen v\u00e6rtsn\u00f8gle, som SSH-klienten vil anse for at v\u00e6re m\u00e5lhostens n\u00f8gle, medmindre der udf\u00f8res en kontrol af n\u00f8glefingeraftrykket. Dette muligg\u00f8r, at angriberen kan udf\u00f8re en MITM uden at v\u00e6kke brugerens mistanke og ignorere sessioner, hvor klienten allerede har cachet v\u00e6rtsn\u00f8gler, hvis fors\u00f8g p\u00e5 at \u00e6ndre dem vil resultere i en advarsel om \u00e6ndring af v\u00e6rtsn\u00f8glen. Angrebet er baseret p\u00e5 brugernes uforsigtighed, idet de ikke udf\u00f8rer manuel kontrol af v\u00e6rtsn\u00f8glefingeraftrykket ved f\u00f8rste forbindelse. De, der kontrollerer fingeraftryk, er beskyttet mod s\u00e5danne angreb.<\/p>\n

Som et tegn til at identificere den f\u00f8rste forbindelse anvendes r\u00e6kkef\u00f8lgen af de underst\u00f8ttede algoritmer for v\u00e6rtsn\u00f8gler. Hvis det er den f\u00f8rste forbindelse, sender klienten som standard en liste over algoritmer, og hvis v\u00e6rtsn\u00f8glen allerede er i cachen, placeres den tilknyttede algoritme \u00f8verst (algoritmer sorteres efter pr\u00e6ference). <\/p>\n

Problemet optr\u00e6der i versioner af OpenSSH fra 5.7 til 8.3 og i PuTTY fra 0.68 til 0.73. Problemet er blevet l\u00f8st<\/a><\/noindex> i versionen PuTTY 0.74<\/a><\/noindex> gennem tilf\u00f8jelse af muligheden for at deaktivere den dynamiske oprettelse af lister over algoritmer til behandling af v\u00e6rtsn\u00f8gler til fordel for en konstant r\u00e6kkef\u00f8lge af algoritmer.<\/p>\n

OpenSSH-projektet har ikke planer om at \u00e6ndre SSH-klientens adf\u00e6rd, idet der, hvis algoritmen for den eksisterende n\u00f8gle ikke angives f\u00f8rst, vil blive fors\u00f8gt at anvende en algoritme, der ikke svarer til den cacherede n\u00f8gle, med en advarsel om en ukendt n\u00f8gle. Det vil sige, der opst\u00e5r et valg \u2014 enten informationsl\u00e6kage (OpenSSH og PuTTY) eller advarsler om n\u00f8gleskift (Dropbear SSH), hvis den gemte n\u00f8gle ikke svarer til den f\u00f8rste algoritme p\u00e5 standardlisten.<\/p>\n

For at sikre beskyttelse i OpenSSH anbefales det at bruge alternative metoder til at kontrollere v\u00e6rtsn\u00f8glen ved hj\u00e6lp af SSHFP-poster i DNSSEC og v\u00e6rtscertifikater (PKI). Det er ogs\u00e5 muligt at deaktivere den adaptive valg af algoritmer til v\u00e6rtsn\u00f8gler via indstillingen HostKeyAlgorithms og bruge indstillingen UpdateHostKeys til at f\u00e5 ekstra v\u00e6rtsn\u00f8gler efter autentificeringen.<\/p>\n

<\/a><\/noindex><\/p>\n

Kilde: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\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 (CVE-2020-14002 \u0432 PuTTY \u0438 CVE-2020-14145 \u0432 OpenSSH), \u043f\u0440\u0438\u0432\u043e\u0434\u044f\u0449\u0430\u044f \u043a \u0443\u0442\u0435\u0447\u043a\u0435 \u0441\u0432\u0435\u0434\u0435\u043d\u0438\u0439 \u0432 \u0430\u043b\u0433\u043e\u0440\u0438\u0442\u043c\u0435 \u0441\u043e\u0433\u043b\u0430\u0441\u043e\u0432\u0430\u043d\u0438\u044f \u0441\u043e\u0435\u0434\u0438\u043d\u0435\u043d\u0438\u044f. \u0423\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u0435\u0442 \u0430\u0442\u0430\u043a\u0443\u044e\u0449\u0435\u043c\u0443, \u0441\u043f\u043e\u0441\u043e\u0431\u043d\u043e\u043c\u0443 \u043f\u0435\u0440\u0435\u0445\u0432\u0430\u0442\u0438\u0442\u044c \u0442\u0440\u0430\u0444\u0438\u043a \u043a\u043b\u0438\u0435\u043d\u0442\u0430 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