{"id":35396,"date":"2019-10-31T22:04:04","date_gmt":"2019-10-31T19:04:04","guid":{"rendered":"https:\/\/prohoster.info\/blog\/uyazvimosti-v-tcp-stekah-linux-i-freebsd-privodyashhie-k-udalyonnomu-otkazu-v-obsluzhivanii\/"},"modified":"2019-10-31T22:04:04","modified_gmt":"2019-10-31T19:04:04","slug":"uyazvimosti-v-tcp-stekah-linux-i-freebsd-privodyashhie-k-udalyonnomu-otkazu-v-obsluzhivanii","status":"publish","type":"post","link":"https:\/\/prohoster.info\/da\/blog\/news\/uyazvimosti-v-tcp-stekah-linux-i-freebsd-privodyashhie-k-udalyonnomu-otkazu-v-obsluzhivanii","title":{"rendered":"S\u00e5rbarheder i TCP-stakke i Linux og FreeBSD, der f\u00f8rer til fjern-afbrydelse af tjenesten","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Netflix har afsl\u00f8ret<\/a><\/noindex> flere kritiske af s\u00e5rbarheder<\/a><\/noindex> i TCP-stakke i Linux og FreeBSD, som muligg\u00f8r fjerninitiering af kernefejl eller for\u00e5rsager overforbrug af ressourcer ved behandling af specielt formaterede TCP-pakker (packet-of-death). Problemerne skyldes<\/a><\/noindex> fejl i h\u00e5ndteringen af maksimal blokst\u00f8rrelse i TCP-pakken (MSS, Maximum Segment Size) og mekanismen til selektiv bekr\u00e6ftelse af forbindelser (SACK, TCP Selective Acknowledgement).<\/p>\n

  • CVE-2019-11477<\/a><\/noindex> (SACK Panic) \u2014 problemet opst\u00e5r i Linux-kernene fra 2.6.29 og g\u00f8r det muligt at for\u00e5rsage en kernel panic ved at sende en r\u00e6kke SACK-pakker, hvilket skyldes et heltals overflow i h\u00e5ndteringen. For angrebet er det tilstr\u00e6kkeligt at indstille MSS-v\u00e6rdien for TCP-forbindelsen til 48 byte (den nedre gr\u00e6nse, der s\u00e6tter segmentst\u00f8rrelsen til 8 byte) og sende en sekvens af specifikt sammensatte SACK-pakker.\n

    Som en beskyttelsesomvej kan man deaktivere h\u00e5ndteringen af SACK (indtaste 0 i \/proc\/sys\/net\/ipv4\/tcp_sack) eller blokere<\/a><\/noindex> forbindelser med lav MSS (virker kun ved at s\u00e6tte sysctl net.ipv4.tcp_mtu_probing til 0 og kan forstyrre nogle normale forbindelser med lav MSS);<\/p>\n

  • CVE-2019-11478<\/a><\/noindex> (SACK Slowness) \u2014 f\u00f8rer til forstyrrelser i SACK-mekanismen (n\u00e5r der bruges en Linux-kerne \u00e6ldre end 4.15) eller til overdreven ressourceforbrug. Problemet opst\u00e5r under behandlingen af specielt udformede SACK-pakker, som kan bruges til at fragmentere retransmissionsk\u00f8en (TCP retransmission). Omg\u00e5elsesmetoderne til beskyttelse ligner dem fra den tidligere s\u00e5rbarhed;\n
  • CVE-2019-5599<\/a><\/noindex> (SACK Slowness) \u2014 g\u00f8r det muligt at for\u00e5rsage fragmentering af kortet afsendte pakker under behandlingen af en s\u00e6rlig sekvens af SACK inden for en enkelt TCP-forbindelse og for\u00e5rsage udf\u00f8relsen af ressourcekr\u00e6vende operationer i listegennems\u00f8gning. Problemet opst\u00e5r i FreeBSD 12 med RACK-pakkeforl\u00e6ggelsesmekanismen. Som en omg\u00e5elsesmetode kan RACK-modulet deaktiveres;\n
  • CVE-2019-11479<\/a><\/noindex> \u2014 angriberen kan f\u00e5 Linux-kernen til at opdele svarene i flere TCP-segmenter, hvor hver af dem kun indeholder 8 byte data, hvilket kan f\u00f8re til en betydelig stigning i trafik, \u00f8get CPU-belastning og overbelastning af kommunikationskanalen. Som en beskyttelsesmetode anbefales det blokere<\/a><\/noindex> blokere forbindelser med lav MSS.\n<\/ul>\n

    I Linux-kernen er problemerne l\u00f8st i versionerne 4.4.182, 4.9.182, 4.14.127, 4.19.52 og 5.1.11. Rettelsen for FreeBSD er tilg\u00e6ngelig i form af et patch<\/a><\/noindex>. I distributions er pakkeopdateringer med kernen allerede udgivet til Debian<\/a><\/noindex>, RHEL<\/a><\/noindex>, SUSE\/openSUSE<\/a><\/noindex>. Rettelse under forberedelse i Ubuntu<\/a><\/noindex>, Fedora<\/a><\/noindex> og Arch Linux<\/a><\/noindex>.<\/p>\n

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

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

    \u041a\u043e\u043c\u043f\u0430\u043d\u0438\u044f Netflix \u0432\u044b\u044f\u0432\u0438\u043b\u0430 \u043d\u0435\u0441\u043a\u043e\u043b\u044c\u043a\u043e \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u0438\u0445 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0435\u0439 \u0432 TCP-\u0441\u0442\u0435\u043a\u0430\u0445 Linux \u0438 FreeBSD, \u043a\u043e\u0442\u043e\u0440\u044b\u0435 \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0442 \u0443\u0434\u0430\u043b\u0451\u043d\u043d\u043e \u0438\u043d\u0438\u0446\u0438\u0438\u0440\u043e\u0432\u0430\u0442\u044c \u043a\u0440\u0430\u0445 \u044f\u0434\u0440\u0430 \u0438\u043b\u0438 \u0432\u044b\u0437\u0432\u0430\u0442\u044c \u0447\u0440\u0435\u0437\u043c\u0435\u0440\u043d\u043e\u0435 \u043f\u043e\u0442\u0440\u0435\u0431\u043b\u0435\u043d\u0438\u0435 \u0440\u0435\u0441\u0443\u0440\u0441\u043e\u0432 \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\u044b\u0445 TCP-\u043f\u0430\u043a\u0435\u0442\u043e\u0432 (packet-of-death). \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u044b \u0432\u044b\u0437\u0432\u0430\u043d\u044b \u043e\u0448\u0438\u0431\u043a\u0430\u043c\u0438 \u0432 \u043e\u0431\u0440\u0430\u0431\u043e\u0442\u0447\u0438\u043a\u0430\u0445 \u043c\u0430\u043a\u0441\u0438\u043c\u0430\u043b\u044c\u043d\u043e\u0433\u043e \u0440\u0430\u0437\u043c\u0435\u0440\u0430 \u0431\u043b\u043e\u043a\u0430 \u0434\u0430\u043d\u043d\u044b\u0445 \u0432 TCP-\u043f\u0430\u043a\u0435\u0442\u0435 (MSS, Maximum segment size) \u0438 \u043c\u0435\u0445\u0430\u043d\u0438\u0437\u043c\u0430 \u0432\u044b\u0431\u043e\u0440\u043e\u0447\u043d\u043e\u0433\u043e \u043f\u043e\u0434\u0442\u0432\u0435\u0440\u0436\u0434\u0435\u043d\u0438\u044f \u0441\u043e\u0435\u0434\u0438\u043d\u0435\u043d\u0438\u0439 (SACK, TCP Selective Acknowledgement). CVE-2019-11477 (SACK Panic) […]<\/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-35396","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47S\u00e5rbarheder i TCP-stakke p\u00e5 Linux og FreeBSD, der f\u00f8rer til fjernadgang til nedbrud | ProHoster","description":"Virksomheden Netflix har opdaget flere 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