{"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\/cs\/blog\/news\/smtp-smuggling-novaya-tehnika-spufinga-pochtovyh-soobshhenij","title":{"rendered":"SMTP Smuggling \u2014 nov\u00e1 technika spoofingu emailov\u00fdch zpr\u00e1v","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

V\u00fdzkumn\u00edci spole\u010dnosti SEC Consult zve\u0159ejnili novou techniku spoofingu, kter\u00e1 je zp\u016fsobena nesrovnalostmi ve sledov\u00e1n\u00ed specifikace v r\u016fzn\u00fdch implementac\u00edch protokolu SMTP. Navrhovan\u00e1 technika \u00fatoku umo\u017e\u0148uje rozd\u011blit jednu zpr\u00e1vu na n\u011bkolik r\u016fzn\u00fdch zpr\u00e1v p\u0159i jej\u00edm p\u0159enosu z p\u016fvodn\u00edho SMTP serveru na jin\u00fd SMTP server, kter\u00fd interpretuje sekvenci pro rozd\u011blen\u00ed zpr\u00e1v p\u0159en\u00e1\u0161en\u00fdch jedn\u00edm spojen\u00edm odli\u0161n\u011b. Metoda m\u016f\u017ee b\u00fdt pou\u017eita k odes\u00edl\u00e1n\u00ed fale\u0161n\u00fdch zpr\u00e1v jm\u00e9nem jin\u00fdch odes\u00edlatel\u016f v po\u0161tovn\u00edch slu\u017eb\u00e1ch, kter\u00e9 ov\u011b\u0159uj\u00ed p\u016fvodn\u00edho odes\u00edlatele. <\/p>\n

Probl\u00e9m je zp\u016fsoben t\u00edm, \u017ee r\u016fzn\u00e9 SMTP servery r\u016fzn\u011b interpretuj\u00ed sekvenci konce dat, co\u017e m\u016f\u017ee v\u00e9st k rozd\u011blen\u00ed jednoho e-mailu na n\u011bkolik v r\u00e1mci jednoho sezen\u00ed s SMTP serverem. Ve specifikaci pro ozna\u010den\u00ed konce p\u0159enosu e-mailu je definov\u00e1na sekvence «\r\n\r\n» (te\u010dka ohrani\u010den\u00e1 znaky n\u00e1vratov\u00e9ho znaku a nov\u00e9ho \u0159\u00e1dku). Po t\u00e9to sekvenci mohou n\u00e1sledovat p\u0159\u00edkazy pro odesl\u00e1n\u00ed dal\u0161\u00edho e-mailu bez p\u0159eru\u0161en\u00ed spojen\u00ed. N\u011bkter\u00e9 SMTP servery striktn\u011b dodr\u017euj\u00ed p\u0159edpis, ale jin\u00e9, pro zaji\u0161t\u011bn\u00ed kompatibility s n\u011bkter\u00fdmi vz\u00e1cn\u00fdmi po\u0161tovn\u00edmi klienty, zpracov\u00e1vaj\u00ed jako odd\u011blova\u010de i takov\u00e9 sekvence jako «\n\n», «\n\r\n», «\r\n\n», «\r.\r», «\r\n0.\r\n» a «\r\n0.\r\n». <\/p>\n

\u00datok spo\u010d\u00edv\u00e1 v tom, \u017ee na prvn\u00ed server<\/a>, kter\u00fd zpracov\u00e1v\u00e1 pouze odd\u011blova\u010d «\r\n\r\n» odes\u00edl\u00e1 e-mail, jeho\u017e t\u011blo obsahuje alternativn\u00ed odd\u011blova\u010d, nap\u0159\u00edklad «\r\r», za kter\u00fdm n\u00e1sleduj\u00ed p\u0159\u00edkazy pro odesl\u00e1n\u00ed druh\u00e9 zpr\u00e1vy. Proto\u017ee prvn\u00ed server striktn\u011b dodr\u017euje specifikaci, zpracov\u00e1v\u00e1 obdr\u017eenou sekvenci jako jeden e-mail. Pokud je pot\u00e9 e-mail sm\u011brov\u00e1n na tranzitn\u00ed server nebo server p\u0159\u00edjemce, kter\u00fd nav\u00edc vn\u00edm\u00e1 sekvenci «\r\r» jako odd\u011blova\u010d, bude zpracov\u00e1n jako dv\u011b samostatn\u011b odeslan\u00e9 e-maily (druh\u00fd e-mail m\u016f\u017ee b\u00fdt odesl\u00e1n jm\u00e9nem u\u017eivatele, kter\u00fd nebyl autentizov\u00e1n p\u0159es «AUTH LOGIN», ale na stran\u011b p\u0159\u00edjemce se bude jevit jako platn\u00fd).

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

Jako p\u0159\u00edklady SMTP server\u016f a slu\u017eeb, kter\u00e9 povoluj\u00ed alternativn\u00ed odd\u011blova\u010de, lze uv\u00e9st Postfix, Sendmail, MS Exchange Online a Cisco Secure Email Gateway, a mezi po\u0161tovn\u00edmi slu\u017ebami, kter\u00e9 nefilteruj\u00ed nespr\u00e1vn\u00e9 odd\u011blova\u010de z e-mail\u016f p\u0159i spojen\u00ed s jin\u00fdmi servery \u2014 GMX, iCloud a Microsoft Outlook. <\/p>\n

Aby se zabr\u00e1nilo probl\u00e9mu v Postfixu ve verz\u00edch 3.8.1, 3.7.6, 3.6.10 a 3.5.20, byla p\u0159id\u00e1na konfigurace «smtpd_forbid_unauth_pipelining», kter\u00e1 p\u0159eru\u0161\u00ed spojen\u00ed v p\u0159\u00edpad\u011b pou\u017eit\u00ed odd\u011blova\u010d\u016f, kter\u00e9 nevyhovuj\u00ed po\u017eadavk\u016fm RFC 2920 a RFC 5321. V sou\u010dasnosti je tato konfigurace ve v\u00fdchoz\u00edm nastaven\u00ed vypnuta, ale pl\u00e1nuje se jej\u00ed aktivace ve v\u00fdchoz\u00edm nastaven\u00ed ve v\u011btvi Postfix 3.9, kter\u00e1 se o\u010dek\u00e1v\u00e1 na ja\u0159e 2024. V\u011btvi 3.9 tak\u00e9 bude zahrnuta konfigurace smtpd_forbid_bare_newline, kter\u00e1 vyvol\u00e1 chybu p\u0159i pou\u017eit\u00ed pouze znaku nov\u00e9ho \u0159\u00e1dku («\n») k odd\u011blen\u00ed \u0159\u00e1dk\u016f, co\u017e poru\u0161uje RFC 5321. <\/p>\n

V o\u010dek\u00e1van\u00e9m vyd\u00e1n\u00ed Sendmail 8.18.0.2 pro ochranu p\u0159ed \u00fatokem je v srv_features navr\u017eena volba ‘o’, kter\u00e1 umo\u017e\u0148uje zpracov\u00e1n\u00ed pouze sekvence «\r\n.\r\n». Upozor\u0148uje se, \u017ee vypnut\u00ed podpory alternativn\u00edch odd\u011blova\u010d\u016f m\u016f\u017ee naru\u0161it funk\u010dnost n\u011bkter\u00fdch vz\u00e1cn\u00fdch emailov\u00fdch klient\u016f, kter\u00e9 zcela neodpov\u00eddaj\u00ed specifikaci SMTP.
\n
Zdroj: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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