{"id":55807,"date":"2020-01-29T00:00:00","date_gmt":"2020-01-28T21:00:00","guid":{"rendered":"https:\/\/prohoster.info\/blog\/blog_prohoster\/uyazvimost-v-opensmtpd-pozvolyayushhaya-udalyonno-vypolnit-kod-s-pravami-root"},"modified":"2020-02-18T14:03:57","modified_gmt":"2020-02-18T11:03:57","slug":"uyazvimost-v-opensmtpd-pozvolyayushhaya-udalyonno-vypolnit-kod-s-pravami-root","status":"publish","type":"post","link":"https:\/\/prohoster.info\/sq\/blog\/news\/uyazvimost-v-opensmtpd-pozvolyayushhaya-udalyonno-vypolnit-kod-s-pravami-root","title":{"rendered":"Nj\u00eb dob\u00ebsi n\u00eb OpenSMTPD, e cila lejon ekzekutimin e kodit n\u00eb distanc\u00eb me privilegje root","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

N\u00eb projektin e zhvilluar OpenBSD p\u00ebr serverin e post\u00ebs , shum\u00ebpjes\u00ebshi i terminalit tekstual (analog i GNU screen)<\/a><\/noindex> u identifikua nj\u00eb dob\u00ebsi kritike<\/a><\/noindex> (CVE-2020-7247), e cila lejon ekzekutimin e komandave shell n\u00eb server me t\u00eb drejtat e p\u00ebrdoruesit root. Vulnerabiliteti u identifikua gjat\u00eb nj\u00eb auditi t\u00eb rip\u00ebrs\u00ebritur, t\u00eb kryer nga kompania Qualys Security (auditi i m\u00ebparsh\u00ebm i OpenSMTPD ishte kryer n\u00eb vitin 2015, nd\u00ebrsa vulnerabiliteti i ri \u00ebsht\u00eb prezent q\u00eb nga maji i vitit 2018). u krye<\/a><\/noindex> n\u00eb vitin 2015, dhe vulnerabiliteti i ri \u00ebsht\u00eb prezent q\u00eb nga maji i vitit 2018). Problemi i eliminuar<\/a><\/noindex> jan\u00eb l\u00ebshuar n\u00eb versionin OpenSMTPD 6.6.2. T\u00eb gjith\u00eb p\u00ebrdoruesve u rekomandohet t\u00eb instalojn\u00eb menj\u00ebher\u00eb p\u00ebrdit\u00ebsimin (p\u00ebr OpenBSD, rregullimi mund t\u00eb instalohet p\u00ebrmes syspatch).<\/p>\n

Jan\u00eb propozuar dy variante sulmi. Varianti i par\u00eb funksionon n\u00eb konfigurimin e paracaktuar t\u00eb OpenSMTPD (pranimi i k\u00ebrkesave vet\u00ebm nga localhost) dhe lejon shfryt\u00ebzimin e problemit n\u00eb m\u00ebnyr\u00eb lokale, kur sulmuesi ka mund\u00ebsin\u00eb t\u00eb qasje n\u00eb nd\u00ebrfaqen lokale t\u00eb rrjetit (loopback) n\u00eb server (p.sh., n\u00eb sistemet e hostimit). Varianti i dyt\u00eb shfaqet n\u00eb rastin e konfigurimit t\u00eb OpenSMTPD p\u00ebr pranimin e k\u00ebrkesave t\u00eb jashtme t\u00eb rrjetit (serveri i post\u00ebs, q\u00eb pranon email nga pal\u00eb t\u00eb treta). K\u00ebrkuesit kan\u00eb p\u00ebrgatitur nj\u00eb prototip t\u00eb eksploitit, i cili funksionon me sukses si me variantin OpenSMTPD t\u00eb p\u00ebrfshir\u00eb n\u00eb OpenBSD 6.6, ashtu edhe me versionin e portuar p\u00ebr sisteme t\u00eb tjera operative (i testuar n\u00eb Debian Testing).<\/p>\n

Problemi \u00ebsht\u00eb shkaktuar nga nj\u00eb gabim n\u00eb funksionin smtp_mailaddr(), i cili thirret p\u00ebr t\u00eb verifikuar sakt\u00ebsin\u00eb e vlerave n\u00eb fushat \u00abMAIL FROM\u00bb dhe \u00abRCPT TO\u00bb, q\u00eb p\u00ebrcaktojn\u00eb d\u00ebrguesin\/pranuesin dhe d\u00ebrgohen gjat\u00eb lidhjes me serverin e post\u00ebs. P\u00ebr t\u00eb kontrolluar pjes\u00ebn e adres\u00ebs s\u00eb post\u00ebs q\u00eb shkon para simbolit \u00ab@\u00bb, n\u00eb smtp_mailaddr() thirret funksioni
\nvalid_localpart(), i cili konsideron si t\u00eb lejueshme (MAILADDR_ALLOWED) simbolet \u00ab!#$%\u2019*?\/^`{|}~+-=_\u00bb, sipas k\u00ebrkesave t\u00eb RFC 5322. <\/p>\n

N\u00eb k\u00ebt\u00eb rast, ekrani i drejtp\u00ebrdrejt\u00eb i vargut b\u00ebhet n\u00eb funksionin mda_expand_token(), i cili z\u00ebvend\u00ebson vet\u00ebm simbolet \u00ab!#$%\u2019*?`{|}~\u00bb (MAILADDR_ESCAPE). M\u00eb pas, vargu i p\u00ebrgatitur n\u00eb mda_expand_token() p\u00ebrdoret gjat\u00eb thirrjes s\u00eb agentit t\u00eb shp\u00ebrndarjes (MDA) me komand\u00ebn \u2018execle(\u2018\/bin\/sh\u2019, \u2018\/bin\/sh\u2019, \u2018-c\u2019, mda_command,\u2026\u2019. N\u00eb rastin e vendosjes s\u00eb let\u00ebrsi n\u00eb mbox p\u00ebrmes \/bin\/sh, aktivizohet vargu \u2018\/usr\/libexec\/mail.local -f %{mbox.from} %{user.username}\u2019, ku vlera \u2018%{mbox.from}\u2019 p\u00ebrfshin t\u00eb dh\u00ebnat e ekranuara nga parametri \u2018MAIL FROM\u2019.<\/p>\n

Esenca e dob\u00ebsis\u00eb q\u00ebndron n\u00eb faktin se smtp_mailaddr() ka nj\u00eb gabim logjik, p\u00ebr shkak t\u00eb t\u00eb cilit n\u00eb rast se d\u00ebrgohet nj\u00eb domen i zbraz\u00ebt n\u00eb email, funksioni kthen nj\u00eb kod t\u00eb suksessh\u00ebm verifikimi, edhe n\u00ebse pjesa e adres\u00ebs para \u00ab@\u00bb p\u00ebrmban simbole t\u00eb pap\u00ebrshtatshme. M\u00eb pas, gjat\u00eb p\u00ebrgatitjes s\u00eb vargut nga funksioni mda_expand_token(), nuk ekranohet \u00e7do simbol i mundsh\u00ebm special t\u00eb shell-it, por vet\u00ebm simbolet speciale t\u00eb lejuara n\u00eb adres\u00ebn e post\u00ebs. K\u00ebshtu, p\u00ebr t\u00eb aktivizuar komand\u00ebn e tij, mjafton t\u00eb p\u00ebrdoret n\u00eb pjes\u00ebn lokale t\u00eb emailit simboli \u2018;\u2019 dhe hap\u00ebsira, t\u00eb cilat nuk jan\u00eb n\u00eb grupin MAILADDR_ESCAPE dhe nuk ekranohet. P\u00ebr shembull:<\/p>\n

$ nc 127.0.0.1 25<\/p>\n

HELO professor.falken
\n MAIL FROM:
\n RCPT TO:
\n DATA
\n .
\n QUIT<\/p>\n

Pas k\u00ebsaj seance, OpenSMTPD do t\u00eb ekzekutoj\u00eb n\u00eb mbox komand\u00ebn p\u00ebrmes shell <\/p>\n

\/usr\/libexec\/mail.local -f ;sleep 66; root<\/p>\n

K\u00ebshtu, mund\u00ebsit\u00eb e sulmit kufizohen nga fakti q\u00eb pjesa lokale e adres\u00ebs nuk mund t\u00eb tejkaloj\u00eb 64 simbole, dhe simbolet speciale \u2018$\u2019 dhe \u2018|\u2019 z\u00ebvend\u00ebsohen me \u2018:\u2019 gjat\u00eb ekranuarit. P\u00ebr t\u00eb anashkaluar k\u00ebt\u00eb kufizim, \u00ebsht\u00eb shfryt\u00ebzuar fakti se p\u00ebrmbajtja e letr\u00ebs kalon pas aktivizimit t\u00eb \/usr\/libexec\/mail.local p\u00ebrmes rrjedh\u00ebs hyr\u00ebse, dmth. p\u00ebrmes manipulimeve me adres\u00ebn, mund t\u00eb aktivizohet vet\u00ebm interpretuese e komandave sh dhe t\u00eb p\u00ebrdoret p\u00ebrmbajtja e letr\u00ebs si nj\u00eb grup instrukcionesh. Duke qen\u00eb se n\u00eb fillim t\u00eb letr\u00ebs jan\u00eb specifikuar titujt e sh\u00ebrbimeve SMTP, propozohet t\u00eb p\u00ebrdoret thirrja e komand\u00ebs read n\u00eb cik\u00ebl p\u00ebr t'i kaluar ata. Eksploiti funksional merr nj\u00eb form\u00eb t\u00eb till\u00eb:<\/p>\n

$ nc 192.168.56.143 25<\/p>\n

HELO professor.falken
\n MAIL FROM:
\n RCPT TO:
\n DATA
\n #0
\n #1
\n …
\n #d
\n for i in W O P R; do
\n echo -n \u2018($i) \u2018 && id || break
\n done > \/root\/x.`id -u`. $$
\n .
\n QUIT<\/p>\n

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

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

\u0412 \u0440\u0430\u0437\u0432\u0438\u0432\u0430\u0435\u043c\u043e\u043c \u043f\u0440\u043e\u0435\u043a\u0442\u043e\u043c OpenBSD \u043f\u043e\u0447\u0442\u043e\u0432\u043e\u043c \u0441\u0435\u0440\u0432\u0435\u0440\u0435 OpenSMTPD \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u0430\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c (CVE-2020-7247), \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0430\u044f \u0443\u0434\u0430\u043b\u0451\u043d\u043d\u043e \u0432\u044b\u043f\u043e\u043b\u043d\u0438\u0442\u044c shell-\u043a\u043e\u043c\u0430\u043d\u0434\u044b \u043d\u0430 \u0441\u0435\u0440\u0432\u0435\u0440\u0435 \u0441 \u043f\u0440\u0430\u0432\u0430\u043c\u0438 \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u044f root. \u0423\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u0430 \u0432 \u0445\u043e\u0434\u0435 \u043f\u043e\u0432\u0442\u043e\u0440\u043d\u043e\u0433\u043e \u0430\u0443\u0434\u0438\u0442\u0430, \u043f\u0440\u043e\u0432\u0435\u0434\u0451\u043d\u043d\u043e\u0433\u043e \u043a\u043e\u043c\u043f\u0430\u043d\u0438\u0435\u0439 Qualys Security (\u043f\u0440\u043e\u0448\u043b\u044b\u0439 \u0430\u0443\u0434\u0438\u0442 OpenSMTPD \u043f\u0440\u043e\u0432\u043e\u0434\u0438\u043b\u0441\u044f \u0432 2015 \u0433\u043e\u0434\u0443, \u0430 \u043d\u043e\u0432\u0430\u044f \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c \u043f\u0440\u0438\u0441\u0443\u0442\u0441\u0442\u0432\u0443\u0435\u0442 \u0441 \u043c\u0430\u044f 2018 \u0433\u043e\u0434\u0430). \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u0430 \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u0430 \u0432 \u0432\u044b\u043f\u0443\u0441\u043a\u0435 OpenSMTPD 6.6.2. \u0412\u0441\u0435\u043c \u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u044f\u043c \u0440\u0435\u043a\u043e\u043c\u0435\u043d\u0434\u0443\u0435\u0442\u0441\u044f […]<\/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-55807","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\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\udd47Vulnerabiliteti n\u00eb OpenSMTPD, q\u00eb lejon ekzekutimin e kodit me t\u00eb drejtat e root | ProHoster","description":"N\u00eb projektin n\u00eb zhvillim OpenBSD p\u00ebr serverin e post\u00ebs OpenSMTPD u 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