{"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\/sv\/blog\/news\/uyazvimosti-v-tcp-stekah-linux-i-freebsd-privodyashhie-k-udalyonnomu-otkazu-v-obsluzhivanii","title":{"rendered":"S\u00e5rbarheter i TCP-staplarna Linux och FreeBSD som leder till en fj\u00e4rrutl\u00f6sning av tj\u00e4nsteavbrott","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

F\u00f6retaget Netflix har identifierat<\/a><\/noindex> flera kritiska s\u00e5rbarheter<\/a><\/noindex> i TCP-staplarna Linux och FreeBSD, som g\u00f6r det m\u00f6jligt att fj\u00e4rrinitiera en k\u00e4rnkrasch eller orsaka \u00f6verdriven resursf\u00f6rbrukning vid hantering av specifikt formaterade TCP-paket (packet-of-death). Problemen orsakas av<\/a><\/noindex> fel i hanterarna f\u00f6r maximal storlek p\u00e5 datablokkar i TCP-paket (MSS, Maximum Segment Size) och mekanismen f\u00f6r selektiv bekr\u00e4ftelse av anslutningar (SACK, TCP Selective Acknowledgement).<\/p>\n

  • CVE-2019-11477<\/a><\/noindex> (SACK Panic) \u2014 problemet uppst\u00e5r i Linux-k\u00e4rnor fr\u00e5n version 2.6.29 och g\u00f6r det m\u00f6jligt att orsaka en k\u00e4rnkrash (panic) genom att skicka en serie SACK-paket p\u00e5 grund av ett heltals\u00f6verskridande i hanteraren. F\u00f6r attacken \u00e4r det tillr\u00e4ckligt att s\u00e4tta v\u00e4rdet MSS till 48 byte f\u00f6r TCP-anslutningen (minimi gr\u00e4ns som st\u00e4ller in segmentets storlek till 8 byte) och skicka en sekvens av specifikt sammanst\u00e4llda SACK-paket.\n

    Som skydd \u00e4r det m\u00f6jligt att st\u00e4nga av hanteringen av SACK (skriver 0 i \/proc\/sys\/net\/ipv4\/tcp_sack) eller blockera<\/a><\/noindex> anslutningar med l\u00e5g MSS (fungerar endast om sysctl net.ipv4.tcp_mtu_probing s\u00e4tts till 0 och kan p\u00e5verka vissa normala anslutningar med l\u00e5g MSS);<\/p>\n

  • CVE-2019-11478<\/a><\/noindex> (SACK Slowness) \u2014 leder till st\u00f6rningar i SACK-mekanismen (vid anv\u00e4ndning av Linux-k\u00e4rnor \u00e4ldre \u00e4n 4.15) eller \u00f6verdriven resursanv\u00e4ndning. Problemet uppst\u00e5r vid bearbetning av speciellt utformade SACK-paket som kan anv\u00e4ndas f\u00f6r att fragmentera k\u00f6erna f\u00f6r om\u00f6verf\u00f6ring (TCP retransmission). \u00c5tg\u00e4rderna f\u00f6r att kringg\u00e5 skyddet \u00e4r desamma som f\u00f6r den f\u00f6reg\u00e5ende s\u00e5rbarheten;\n
  • CVE-2019-5599<\/a><\/noindex> (SACK Slowness) \u2014 g\u00f6r det m\u00f6jligt att \u00e5stadkomma fragmentering av kartan \u00f6ver skickade paket vid bearbetning av en speciell sekvens SACK inom en enda TCP-anslutning och orsaka en resurskr\u00e4vande operation av att g\u00e5 igenom listan. Problemet uppst\u00e5r i FreeBSD 12 med mekanismen f\u00f6r att identifiera paketf\u00f6rluster RACK. Som en tillf\u00e4llig l\u00f6sning kan RACK-modulen st\u00e4ngas av;\n
  • CVE-2019-11479<\/a><\/noindex> \u2014 en angripare kan orsaka uppdelning av svaren i k\u00e4rnan Linux till flera TCP-segment, var och en som inneh\u00e5ller endast 8 byte data, vilket kan leda till en betydande \u00f6kning av trafik, \u00f6kad CPU-belastning och blockering av kommunikationskanalen. Som en \u00e5tg\u00e4rd f\u00f6r att skydda rekommenderas det blockera<\/a><\/noindex> anslutningar med l\u00e5g MSS.\n<\/ul>\n

    I k\u00e4rnan av Linux har problem \u00e5tg\u00e4rdats i versionerna 4.4.182, 4.9.182, 4.14.127, 4.19.52 och 5.1.11. En l\u00f6sning f\u00f6r FreeBSD finns tillg\u00e4nglig som en patch<\/a><\/noindex>. I distributionerna har paketuppdateringar med k\u00e4rnan redan sl\u00e4ppts f\u00f6r Debian<\/a><\/noindex>, RHEL<\/a><\/noindex>, SUSE\/openSUSE<\/a><\/noindex>. En l\u00f6sning f\u00f6rbereds i Ubuntu<\/a><\/noindex>, Fedora<\/a><\/noindex> och Arch Linux<\/a><\/noindex>.<\/p>\n

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

    K\u00e4lla: 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\u00e5rbarheter i TCP-staplarna i Linux och FreeBSD som leder till en fj\u00e4rravbrott i tj\u00e4nsten | ProHoster","description":"F\u00f6retaget Netflix har identifierat flera 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