{"id":112410,"date":"2023-12-22T03:10:14","date_gmt":"2023-12-22T01:10:16","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/smtp-smuggling-novaya-tehnika-spufinga-pochtovyh-soobshhenij"},"modified":"2023-12-22T03:10:14","modified_gmt":"2023-12-22T01:10:16","slug":"smtp-smuggling-novaya-tehnika-spufinga-pochtovyh-soobshhenij","status":"publish","type":"post","link":"https:\/\/prohoster.info\/da\/blog\/news\/smtp-smuggling-novaya-tehnika-spufinga-pochtovyh-soobshhenij","title":{"rendered":"SMTP Smuggling \u2014 en ny teknik til spoofing af e-mails","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Forskere fra SEC Consult har offentliggjort en ny teknik til spoofing, der skyldes forskelle i overholdelsen af specifikationen i forskellige implementeringer af SMTP-protokollen. Den foresl\u00e5ede angrebsteknik g\u00f8r det muligt at opdele \u00e9n besked til flere forskellige beskeder under overf\u00f8rslen fra en original SMTP-server til en anden SMTP-server, der tolker sekvenserne forskelligt for opdeling af beskeder, der overf\u00f8res over en enkelt forbindelse. Metoden kan bruges til at sende falske beskeder p\u00e5 vegne af andre afsendere i e-mail-tjenester, der verificerer den oprindelige afsender. <\/p>\n

Problemet skyldes, at forskellige SMTP-servere fortolker slutsekvenser af data forskelligt, hvilket kan f\u00f8re til opdeling af en enkelt e-mail i flere i l\u00f8bet af et enkelt session til SMTP-serveren. I specifikationen for markering af slutningen af e-mail-overf\u00f8rslen er sekvensen «\r\n\r\n» (et punkt omgivet af carriage return- og newline-tegn) defineret. Efter denne sekvens kan der f\u00f8lge kommandoer til overf\u00f8rsel af en anden e-mail uden at afbryde forbindelsen. Nogle SMTP-servere f\u00f8lger specifikationen strengt, men andre, for at sikre kompatibilitet med visse sj\u00e6ldne e-mail-klienter, behandler sekvenser som «\n\n», «\n.\r\n», «\r\n.\n», «\r.\r», «\r\n0.\r\n» og «\r\n0.\r\n» som adskillelse. <\/p>\n

Angrebet g\u00e5r ud p\u00e5, at der til den f\u00f8rste server<\/a>, som kun behandler adskillelses-sekvensen «\r\n\r\n», bliver der sendt en e-mail, hvis tekst indeholder en alternativ adskillelse, f.eks. «\r.\r», efterfulgt af kommandoer til at sende en anden besked. Da den f\u00f8rste server strengt f\u00f8lger specifikationen, behandler den den modtagne sekvens som \u00e9n e-mail. Hvis e-mailen derefter sendes til en transitserver eller modtagerens server, som yderligere opfatter sekvensen «\r.\r» som en adskillelse, vil den blive behandlet som to separate sendte e-mails (den anden e-mail kan sendes p\u00e5 vegne af en bruger, der ikke er autentificeret via «AUTH LOGIN», men se korrekt ud for modtageren).

\"SMTP<\/center>
\"SMTP<\/center> <\/p>\n

Eksempler p\u00e5 SMTP-servere og tjenester, der tillader alternative adskillelser, inkluderer Postfix, Sendmail, MS Exchange Online og Cisco Secure Email Gateway, mens e-mail-tjenester, der ikke filtrerer ukorrekte adskillelser fra e-mails ved henvendelse til andre servere, er GMX, iCloud og Microsoft Outlook. <\/p>\n

For blocking the issue in Postfix in releases 3.8.1, 3.7.6, 3.6.10, and 3.5.20, a setting 'smtpd_forbid_unauth_pipelining' has been added, which causes the connection to break if delimiters that do not comply with RFC 2920 and RFC 5321 are used. Currently, this setting is disabled by default, but it is planned to be activated by default in the Postfix 3.9 branch, which is expected in spring 2024. The 3.9 branch will also include the setting smtpd_forbid_bare_newline, which outputs an error when using only the newline character ('\n') to separate lines, violating RFC 5321. <\/p>\n

In the upcoming release of Sendmail 8.18.0.2, an option 'o' has been proposed for protection against attacks in srv_features, which enables the processing of only the sequence '\r\n\r\n'. It is noted that disabling support for alternative delimiters may disrupt the operation of some rare email clients that do not fully adhere to the SMTP specification.
\n
Kilde: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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