{"id":115,"date":"2009-10-23T15:57:24","date_gmt":"2009-10-23T14:57:24","guid":{"rendered":"http:\/\/www.alvaromarin.com\/?p=115"},"modified":"2009-10-23T15:57:24","modified_gmt":"2009-10-23T14:57:24","slug":"proteccion-en-el-kernel-de-freebsd-contra-dos-a-smtp","status":"publish","type":"post","link":"http:\/\/www.alvaromarin.com\/2009\/10\/23\/proteccion-en-el-kernel-de-freebsd-contra-dos-a-smtp\/","title":{"rendered":"Protecci\u00f3n en el kernel de FreeBSD contra DoS a SMTP"},"content":{"rendered":"<p>En la pasada <a href=\"http:\/\/www.ukuug.org\/events\/eurobsdcon2009\/\" target=\"_blank\">EuroBSDCon 2009<\/a> celebrada en Septiembre, un congreso de los <em>hackers<\/em> de FreeBSD, hubo una charla cuyo t\u00edtulo rezaba <em>\u00abFreeBSD kernel protection measures against SMTP DDoS attacks\u00bb<\/em>, por <a href=\"http:\/\/people.freebsd.org\/~mbr\/\" target=\"_blank\">Martin Blapp<\/a>.<\/p>\n<p>El <em>paper<\/em> de aquella charla se puede encontrar en:<\/p>\n<p><a href=\"http:\/\/www.ukuug.org\/events\/eurobsdcon2009\/papers\/BSDCON09-SMTP-DDoS-Final.pdf\" target=\"_blank\">http:\/\/www.ukuug.org\/events\/eurobsdcon2009\/papers\/BSDCON09-SMTP-DDoS-Final.pdf<\/a><\/p>\n<p>Como el propio t\u00edtulo hace suponer, se trata de un m\u00f3dulo (llamado <em>accf_smtp<\/em> para el kernel de FreeBSD capaz de gestionar las conexiones SMTP entrantes al servidor y prevenir cierto tipo de ataques (comunes entre las <em>botnes<\/em>). Con dichas conexiones, puede realizar diversas funciones como hacer una pausa antes de entregar el <em>banner<\/em> del servicio SMTP, rechazar conexiones que no env\u00eden primeramente el comando HELO\/EHLO, establecer n\u00famero m\u00e1ximo de caracteres en par\u00e1metros de comandos&#8230;etc. <\/p>\n<p>Soy de la opini\u00f3n de <a href=\"http:\/\/www.porcupine.org\/wietse\/\" target=\"_blank\">Wietse Venema<\/a> que comentaba que esas funciones no son para hacerlas en el kernel sino en <em>userland<\/em>, como ya hacen numerosos servidores de correo electr\u00f3nico, por lo que en realidad no supone nada nuevo.<\/p>\n<p>Esta idea est\u00e1 basada en el ya existente <em><a href=\"http:\/\/www.gsp.com\/cgi-bin\/man.cgi?section=9&#038;topic=accf_http\" target=\"_blank\">accf_http<\/a><\/em>, que gestiona las conexiones HTTP entrantes. <\/p>\n<p>Habr\u00e1 que esperar a ver qu\u00e9 opinan los que puedan probarlo en sus FreeBSDs.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>En la pasada EuroBSDCon 2009 celebrada en Septiembre, un congreso de los hackers de FreeBSD, hubo una charla cuyo t\u00edtulo rezaba \u00abFreeBSD kernel protection measures against SMTP DDoS attacks\u00bb, por Martin Blapp. El paper de aquella charla se puede encontrar &hellip; 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