{"id":35011,"date":"2019-10-31T22:01:50","date_gmt":"2019-10-31T19:01:50","guid":{"rendered":"https:\/\/prohoster.info\/blog\/kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root\/"},"modified":"2019-10-31T22:01:50","modified_gmt":"2019-10-31T19:01:50","slug":"kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root","status":"publish","type":"post","link":"https:\/\/prohoster.info\/da\/blog\/news\/kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root","title":{"rendered":"Kritisk s\u00e5rbarhed i Exim, der tillader at k\u00f8re kode p\u00e5 serveren med root-rettigheder","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p>I postserver Exim <noindex><a rel=\"nofollow\" href=\"https:\/\/www.openwall.com\/lists\/oss-security\/2019\/06\/05\/4\">opdaget<\/a><\/noindex> kritisk <noindex><a rel=\"nofollow\" href=\"http:\/\/www.exim.org\/static\/doc\/security\/CVE-2019-10149.txt\">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> (<noindex><a rel=\"nofollow\" href=\"https:\/\/security-tracker.debian.org\/tracker\/CVE-2019-10149\">CVE-2019-10149<\/a><\/noindex>), som kan f\u00f8re til fjernudf\u00f8relse af kode p\u00e5 serveren med root-rettigheder ved behandling af en specielt formateret anmodning. Muligheden for udnyttelse af problemet er bem\u00e6rket i versioner fra 4.87 til 4.91 inklusive eller ved bygning med indstillingen EXPERIMENTAL_EVENT.<\/p>\n<p>I standardkonfigurationen kan et angreb udf\u00f8res uden un\u00f8dvendige komplikationer af en lokal bruger, da ACL 'verify = recipient' anvendes, som udf\u00f8rer ekstra tjek for eksterne adresser. Udf\u00f8relsen af et fjernangreb er muligt ved \u00e6ndring af indstillingerne, for eksempel n\u00e5r der arbejdes i rollen som sekund\u00e6r MX for et andet dom\u00e6ne, ved at fjerne ACL 'verify = recipient' eller ved specifikke \u00e6ndringer i local_part_suffix). Et fjernangreb er ogs\u00e5 muligt, hvis en kriminel kan holde forbindelsen til serveren \u00e5ben i 7 dage (for eksempel ved at sende et enkelt byte hvert minut for at omg\u00e5 timeout-afbrydelsen). Det er ikke udelukket, at der ogs\u00e5 er mere enkle angrebsvektorer til fjernudnyttelse af problemet.<\/p>\n<p>S\u00e5rbarheden skyldes en forkert kontrol af modtageradressen i funktionen deliver_message(), der er defineret i filen \/src\/deliver.c. Gennem manipulation af adresseformateringen kan angriberen opn\u00e5 substitution af sine data i argumenterne for kommandoen, der kaldes gennem funktionen execv() med root-rettigheder. Der kr\u00e6ves ikke brug af komplekse teknikker, der anvendes ved bufferoverl\u00f8b eller hukommelsesskader; det er tilstr\u00e6kkeligt blot at erstatte tegn. <\/p>\n<p>Problemet er relateret til anvendelsen af konstruktionen til adressering:<\/p>\n<p>         deliver_localpart = expand_string(<br \/>\n                       string_sprintf('${local_part:%s}', new-&gt;address));<br \/>\n         deliver_domain = expand_string(<br \/>\n                       string_sprintf('${domain:%s}', new-&gt;address));<\/p>\n<p>Funktionen expand_string() fungerer som en overkompliceret maskine, som ogs\u00e5 genkender kommandoen '${run{kommando argumenter}', som f\u00f8rer til udf\u00f8relse af en ekstern behandler. S\u00e5ledes er det tilstr\u00e6kkeligt for en lokal bruger at sende en kommando af formen 'RCPT TO '${username+${run{...}}@localhost}', hvor localhost er en af v\u00e6rtterne i listen over local_domains, og username er navnet p\u00e5 en eksisterende lokal bruger. <\/p>\n<p>Hvis serveren fungerer som en mail relay, er det tilstr\u00e6kkeligt at sende kommandoen 'RCPT TO '${run{...}}@relaydomain.com', hvor relaydomain.com er en af v\u00e6rtterne, der er angivet i indstillingssektionen relay_to_domains. Da der som standard ikke anvendes en privilegiedrop-tilstand i exim (deliver_drop_privilege = false), vil kommandoer sendt via '${run{...}}' blive udf\u00f8rt med root-rettigheder.<\/p>\n<p>Det er bem\u00e6rkelsesv\u00e6rdigt, at s\u00e5rbarheden blev <noindex><a rel=\"nofollow\" href=\"https:\/\/github.com\/Exim\/exim\/commit\/7ea1237c783e380d7bdb86c90b13d8203c7ecf26\">er blevet l\u00f8st<\/a><\/noindex> i udgivelsen 4.92 i februar uden at p\u00e5pege, at rettelsen kunne medf\u00f8re sikkerhedsproblemer. Der er ingen grund til at antage, at udviklerne af Exim bevidst skjulte s\u00e5rbarheden, da problemet blev l\u00f8st under <noindex><a rel=\"nofollow\" href=\"https:\/\/bugs.exim.org\/show_bug.cgi?id=2310\">rettelsen<\/a><\/noindex> af den fejl, der opst\u00e5r ved overf\u00f8rsel af ugyldige adresser, og s\u00e5rbarheden blev identificeret af Qualys under en revision af \u00e6ndringerne i Exim. <\/p>\n<p>Rettelsen til tidligere versioner, som stadig anvendes i distributioner, er kun tilg\u00e6ngelig i form af <noindex><a rel=\"nofollow\" href=\"https:\/\/git.exim.org\/exim.git\/commit\/d740d2111f189760593a303124ff6b9b1f83453d\">et patch<\/a><\/noindex>. Korrigerende udgivelser for tidligere grene med probleml\u00f8sning er planlagt til den 11. juni. Opdateringer af pakker er forberedt til <noindex><a rel=\"nofollow\" href=\"https:\/\/security-tracker.debian.org\/tracker\/CVE-2019-10149\">Debian<\/a><\/noindex>,  <noindex><a rel=\"nofollow\" href=\"https:\/\/people.canonical.com\/~ubuntu-security\/cve\/2019\/CVE-2019-10149.html\">Ubuntu<\/a><\/noindex>, <noindex><a rel=\"nofollow\" href=\"https:\/\/bugzilla.novell.com\/show_bug.cgi?id=CVE-2019-10149\">openSUSE<\/a><\/noindex>. <noindex><a rel=\"nofollow\" href=\"https:\/\/www.archlinux.org\/packages\/community\/x86_64\/exim\/\">Arch Linux<\/a><\/noindex> og <noindex><a rel=\"nofollow\" href=\"https:\/\/bodhi.fedoraproject.org\/updates\/FEDORA-2019-7b741dcaa4\">Fedora<\/a><\/noindex> leverer version 4.92, hvor problemet ikke optr\u00e6der. RHEL og CentOS er ber\u00f8rt, <noindex><a rel=\"nofollow\" href=\"https:\/\/bugzilla.redhat.com\/show_bug.cgi?id=CVE-2019-10149\">er ikke udsat<\/a><\/noindex>da Exim ikke er en del af deres standard pakke-arkiv.<\/p>\n<p><noindex><a rel=\"nofollow\" name=\"link\"><\/a><\/noindex><\/p>\n<p>Kilde: <a \ncontent=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/www.opennet.ru\/opennews\/art.shtml?num=50819\">opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u0412 \u043f\u043e\u0447\u0442\u043e\u0432\u043e\u043c \u0441\u0435\u0440\u0432\u0435\u0440\u0435 Exim \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u0430\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c (CVE-2019-10149), \u043a\u043e\u0442\u043e\u0440\u0430\u044f \u043c\u043e\u0436\u0435\u0442 \u043f\u0440\u0438\u0432\u0435\u0441\u0442\u0438 \u043a \u0443\u0434\u0430\u043b\u0451\u043d\u043d\u043e\u043c\u0443 \u0432\u044b\u043f\u043e\u043b\u043d\u0435\u043d\u0438\u044e \u043a\u043e\u0434\u0430 \u043d\u0430 \u0441\u0435\u0440\u0432\u0435\u0440\u0435 \u0441 \u043f\u0440\u0430\u0432\u0430\u043c\u0438 root \u043f\u0440\u0438 \u043e\u0431\u0440\u0430\u0431\u043e\u0442\u043a\u0435 \u0441\u043f\u0435\u0446\u0438\u0430\u043b\u044c\u043d\u043e \u043e\u0444\u043e\u0440\u043c\u043b\u0435\u043d\u043d\u043e\u0433\u043e \u0437\u0430\u043f\u0440\u043e\u0441\u0430. \u0412\u043e\u0437\u043c\u043e\u0436\u043d\u043e\u0441\u0442\u044c \u044d\u043a\u0441\u043f\u043b\u0443\u0430\u0442\u0430\u0446\u0438\u0438 \u043f\u0440\u043e\u0431\u043b\u0435\u043c\u044b \u043e\u0442\u043c\u0435\u0447\u0435\u043d\u0430 \u0432 \u0432\u0435\u0440\u0441\u0438\u044f\u0445 \u0441 4.87 \u043f\u043e 4.91 \u0432\u043a\u043b\u044e\u0447\u0438\u0442\u0435\u043b\u044c\u043d\u043e \u0438\u043b\u0438 \u043f\u0440\u0438 \u0441\u0431\u043e\u0440\u043a\u0435 \u0441 \u043e\u043f\u0446\u0438\u0435\u0439 EXPERIMENTAL_EVENT. \u0412 \u043a\u043e\u043d\u0444\u0438\u0433\u0443\u0440\u0430\u0446\u0438\u0438 \u043f\u043e \u0443\u043c\u043e\u043b\u0447\u0430\u043d\u0438\u044e \u0430\u0442\u0430\u043a\u0430 \u043c\u043e\u0436\u0435\u0442 \u0431\u044b\u0442\u044c \u0441\u043e\u0432\u0435\u0440\u0448\u0435\u043d\u0430 \u0431\u0435\u0437 \u043b\u0438\u0448\u043d\u0438\u0445 \u0443\u0441\u043b\u043e\u0436\u043d\u0435\u043d\u0438\u0439 \u043b\u043e\u043a\u0430\u043b\u044c\u043d\u044b\u043c \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u043c, [&hellip;]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-35011","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\" content=\"\u0412 \u043f\u043e\u0447\u0442\u043e\u0432\u043e\u043c \u0441\u0435\u0440\u0432\u0435\u0440\u0435 Exim \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u0430\u044f\" \/>\n\t<meta name=\"robots\" content=\"max-image-preview:large\" \/>\n\t<meta name=\"author\" content=\"Yuri Gagarin\"\/>\n\t<link rel=\"canonical\" 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