{"id":82266,"date":"2020-05-20T19:42:07","date_gmt":"2020-05-20T17:42:07","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/udalyonno-ekspluatiruemaya-uyazvimost-v-pochtovom-servere-qmail"},"modified":"2020-05-20T19:42:07","modified_gmt":"2020-05-20T17:42:07","slug":"udalyonno-ekspluatiruemaya-uyazvimost-v-pochtovom-servere-qmail","status":"publish","type":"post","link":"https:\/\/prohoster.info\/hu\/blog\/news\/udalyonno-ekspluatiruemaya-uyazvimost-v-pochtovom-servere-qmail","title":{"rendered":"Proxmox 6.2 'Virtual Environment'","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

A biztons\u00e1gi kutat\u00f3k a Qualys c\u00e9gt\u0151l kimutatt\u00e1k<\/a><\/noindex> lehet\u0151s\u00e9g kihaszn\u00e1l\u00e1s<\/a><\/noindex> sebezhet\u0151s\u00e9gek a qmail levelez\u0151 szerverben, h\u00edres<\/a><\/noindex> m\u00e1r 2005 \u00f3ta (CVE-2005-1513) fenn\u00e1ll, de az\u00f3ta nem jav\u00edtott\u00e1k, mivel a qmail szerz\u0151je azt \u00e1ll\u00edtotta, hogy irre\u00e1lis l\u00e9trehozni egy m\u0171k\u00f6d\u0151 exploitot, amelyet a rendszerek alap\u00e9rtelmezett konfigur\u00e1ci\u00f3ban val\u00f3 t\u00e1mad\u00e1s\u00e1ra lehetne haszn\u00e1lni. A Qualys szakembereinek siker\u00fclt egy exploitet k\u00e9sz\u00edteni, amely megc\u00e1folja ezt a felt\u00e9telez\u00e9st \u00e9s lehet\u0151v\u00e9 teszi a k\u00f3d t\u00e1voli v\u00e9grehajt\u00e1s\u00e1t a szerveren egy k\u00fcl\u00f6n\u00f6sen form\u00e1zott \u00fczenet elk\u00fcld\u00e9s\u00e9vel.<\/p>\n

A probl\u00e9ma egy eg\u00e9sz sz\u00e1m t\u00falcsordul\u00e1sb\u00f3l ered a stralloc_readyplus() f\u00fcggv\u00e9nyben, amely egy nagyon nagy \u00fczenet feldolgoz\u00e1sa sor\u00e1n l\u00e9phet fel. A kihaszn\u00e1l\u00e1shoz 64 bites rendszerre volt sz\u00fcks\u00e9g, amely rendelkezik 4GB-n\u00e1l nagyobb virtu\u00e1lis mem\u00f3ri\u00e1val. A sebezhet\u0151s\u00e9g eredeti elemz\u00e9sekor 2005-ben Daniel Bernstein azt \u00e1ll\u00edtotta, hogy a k\u00f3dban l\u00e9v\u0151 felt\u00e9telez\u00e9s, miszerint a lefoglalt t\u00f6mb m\u00e9rete mindig 32 bites \u00e9rt\u00e9kben van, azon alapul, hogy senki nem ad gigab\u00e1jt mem\u00f3ri\u00e1t minden egyes folyamatnak. Az elm\u00falt 15 \u00e9vben a 64 bites rendszerek a szervereken kiszor\u00edtott\u00e1k a 32 bites v\u00e1ltozatokat, a biztos\u00edtand\u00f3 mem\u00f3ria mennyis\u00e9ge dr\u00e1maian megn\u0151tt, \u00e9s a h\u00e1l\u00f3zati s\u00e1vsz\u00e9less\u00e9g is jelent\u0151sen n\u0151tt. <\/p>\n

A qmailhez kapcsol\u00f3d\u00f3 csomagok figyelembe vett\u00e9k Bernstein megjegyz\u00e9s\u00e9t, \u00e9s a qmail-smtpd folyamat elind\u00edt\u00e1sakor korl\u00e1tozt\u00e1k a rendelkez\u00e9sre \u00e1ll\u00f3 mem\u00f3ri\u00e1t (p\u00e9ld\u00e1ul Debian 10 alatt 7MB limit van be\u00e1ll\u00edtva). De a Qualys m\u00e9rn\u00f6kei kider\u00edtett\u00e9k, hogy ez nem elegend\u0151, \u00e9s a qmail-smtpd mellett egy t\u00e1voli t\u00e1mad\u00e1s a qmail-local folyamat ellen is v\u00e9grehajthat\u00f3, amely az \u00f6sszes ellen\u0151rz\u00f6tt csomagban korl\u00e1tlan maradt. Bizony\u00edt\u00e9k\u00e1ul egy protot\u00edpust k\u00e9sz\u00edtettek, amely alkalmas a Debian csomagban tal\u00e1lhat\u00f3 qmail alap\u00e9rtelmezett konfigur\u00e1ci\u00f3j\u00e1nak t\u00e1mad\u00e1s\u00e1ra.
\nA k\u00f3d t\u00e1voli v\u00e9grehajt\u00e1s\u00e1nak megszervez\u00e9s\u00e9hez 4GB szabad lemezter\u00fclet \u00e9s 8GB RAM sz\u00fcks\u00e9ges a szerveren.
\nAz exploit lehet\u0151v\u00e9 teszi b\u00e1rmilyen shell-parancs futtat\u00e1s\u00e1t b\u00e1rmely felhaszn\u00e1l\u00f3i joggal a rendszerben, kiv\u00e9ve a root-ot \u00e9s a rendszerszint\u0171 felhaszn\u00e1l\u00f3kat, akiknek nincs saj\u00e1t almapp\u00e1juk a \u201e\/home\u201d mapp\u00e1ban (a qmail-local folyamat egy helyi felhaszn\u00e1l\u00f3 jog\u00e1val fut, akinek a lev\u00e9lk\u00e9zbes\u00edt\u00e9se t\u00f6rt\u00e9nik).<\/p>\n

A t\u00e1mad\u00e1s v\u00e9grehajt\u00e1sa
\nnagyon nagy e-mail \u00fczenet k\u00fcld\u00e9s\u00e9n kereszt\u00fcl, amely t\u00f6bb sort tartalmaz a fejl\u00e9cben, k\u00f6r\u00fclbel\u00fcl 4 GB \u00e9s 576 MB m\u00e9retben. Az ilyen sor kezel\u00e9se a qmail-local-ban eg\u00e9sz sz\u00e1m t\u00falcsordul\u00e1st okoz, amikor az \u00fczenetet egy helyi felhaszn\u00e1l\u00f3nak pr\u00f3b\u00e1lj\u00e1k k\u00e9zbes\u00edteni. Az eg\u00e9sz sz\u00e1m t\u00falcsordul\u00e1s ezut\u00e1n puffert\u00falcsordul\u00e1st okoz az adatok m\u00e1sol\u00e1sakor, \u00e9s lehet\u0151s\u00e9get ad a libc k\u00f3dj\u00e1nak \u00edr\u00e1s\u00e1ra a mem\u00f3ri\u00e1ban. Az \u00e1tadott adatok elrendez\u00e9s\u00e9nek manipul\u00e1l\u00e1s\u00e1val lehet\u0151s\u00e9g van arra is, hogy fel\u00fcl\u00edrjuk az \u201eopen()\u201d funkci\u00f3 c\u00edm\u00e9t, helyette a \u201esystem()\u201d funkci\u00f3 c\u00edm\u00e9t adva meg. <\/p>\n

Tov\u00e1bb\u00e1, a qmail-local-ban a qmesearch() h\u00edv\u00e1sakor a \u201e.qmail-extension\u201d f\u00e1jl megnyit\u00e1sa t\u00f6rt\u00e9nik az open() f\u00fcggv\u00e9nyen kereszt\u00fcl, ami t\u00e9nylegesen a system(\".qmail-extension\") f\u00fcggv\u00e9ny futtat\u00e1s\u00e1hoz vezet.
\nMivel a \u201eextension\u201d f\u00e1jl egy r\u00e9sze a c\u00edmzett c\u00edm\u00e9nek a f\u00fcggv\u00e9ny\u00e9ben j\u00f6n l\u00e9tre (p\u00e9ld\u00e1ul: \u201elocaluser-extension@localdomain\u201d), a t\u00e1mad\u00f3k k\u00e9pesek parancsot k\u00fcldeni futtat\u00e1sra az \u201elocaluser-;command;@localdomain\u201d c\u00edmzett megad\u00e1s\u00e1val. <\/p>\n

A k\u00f3d elemz\u00e9se sor\u00e1n k\u00e9t s\u00e9r\u00fcl\u00e9kenys\u00e9get is felfedeztek a qmail-verify kieg\u00e9sz\u00edt\u0151 patchekben, amely a Debian csomag r\u00e9sze. Az els\u0151 s\u00e9r\u00fcl\u00e9kenys\u00e9g (CVE-2020-3811<\/a><\/noindex>) lehet\u0151v\u00e9 teszi az e-mail c\u00edm ellen\u0151rz\u00e9s\u00e9nek megker\u00fcl\u00e9s\u00e9t, a m\u00e1sodik (CVE-2020-3812<\/a><\/noindex>) helyi inform\u00e1ci\u00f3k kisziv\u00e1rg\u00e1s\u00e1hoz vezet. K\u00fcl\u00f6n\u00f6sen az els\u0151 sebezhet\u0151s\u00e9g lehet\u0151v\u00e9 teszi a c\u00edm helyess\u00e9gi ellen\u0151rz\u00e9s\u00e9nek megker\u00fcl\u00e9s\u00e9t, amely az exploit sor\u00e1n a parancs \u00e1tad\u00e1sa sz\u00e1m\u00e1ra haszn\u00e1lt c\u00edm v\u00e9rz\u00e9s\u00e9hez vezet (az ellen\u0151rz\u00e9s nem m\u0171k\u00f6dik olyan c\u00edmek eset\u00e9n, amelyek nem tartalmaznak domaint, mint p\u00e9ld\u00e1ul: \u201elocaluser-;command;\u201d). A m\u00e1sodik sebezhet\u0151s\u00e9g haszn\u00e1lhat\u00f3 a rendszerben, k\u00f6zt\u00fck csak root sz\u00e1m\u00e1ra el\u00e9rhet\u0151 f\u00e1jlok \u00e9s k\u00f6nyvt\u00e1rak ellen\u0151rz\u00e9s\u00e9re, k\u00f6zvetlen h\u00edv\u00e1ssal a helyi feldolgoz\u00f3hoz (a qmail-verify root jogokkal fut).<\/p>\n

A probl\u00e9ma megker\u00fcl\u00e9s\u00e9re Bernstein azt aj\u00e1nlotta, hogy a qmail folyamatokat egy k\u00f6zponti mem\u00f3riahat\u00e1r be\u00e1ll\u00edt\u00e1s\u00e1val ind\u00edts\u00e1k el (\u00bbsoftlimit -m12345678\u00ab), \u00e9s ezzel a probl\u00e9ma blokkol\u00e1sra ker\u00fcl. Alternat\u00edv v\u00e9delmi m\u00f3dk\u00e9nt eml\u00edtik a feldolgozott \u00fczenet maxim\u00e1lis m\u00e9ret\u00e9nek korl\u00e1toz\u00e1s\u00e1t a \u00bbcontrol\/databytes\u00ab f\u00e1jl r\u00e9v\u00e9n (alap\u00e9rtelmezett be\u00e1ll\u00edt\u00e1sok mellett nem hozz\u00e1k l\u00e9tre, \u00edgy a qmail sebezhet\u0151 marad). Ezen k\u00edv\u00fcl a \u00bbcontrol\/databytes\u00ab nem v\u00e9d a rendszeren bel\u00fcli helyi t\u00e1mad\u00e1sok ellen, mivel a korl\u00e1toz\u00e1s csak a qmail-smtpd-ben \u00e9rv\u00e9nyes\u00fcl.<\/p>\n

A probl\u00e9ma a csomagot \u00e9rinti netqmail<\/a><\/noindex>, amely a Debian adatt\u00e1rakban tal\u00e1lhat\u00f3. Ehhez a csomaghoz egy patch-csomag k\u00e9sz\u00fclt, amely elt\u00fcnteti a 2005-\u00f6s r\u00e9gi sebezhet\u0151s\u00e9geket (a mem\u00f3ri\u00e1ra vonatkoz\u00f3 szigor\u00fa korl\u00e1tok k\u00f3dba t\u00f6rt\u00e9n\u0151 be\u00e9p\u00edt\u00e9s\u00e9vel az alloc() funkci\u00f3ban), valamint \u00faj probl\u00e9m\u00e1kat a qmail-verify vonatkoz\u00e1s\u00e1ban. Egyedileg elk\u00e9sz\u00edtett<\/a><\/noindex> friss\u00edtett verzi\u00f3j\u00e1t a qmail-verify patch-nek. A fejleszt\u0151k \u00e1gak<\/a><\/noindex> notqmail<\/a><\/noindex> elk\u00e9sz\u00edtett\u00e9k saj\u00e1t patch-eiket a r\u00e9gi probl\u00e9m\u00e1k blokkol\u00e1s\u00e1ra, \u00e9s megkezdt\u00e9k a lehets\u00e9ges eg\u00e9sz sz\u00e1mok t\u00falt\u00f6lt\u00e9s\u00e9nek kik\u00fcsz\u00f6b\u00f6l\u00e9s\u00e9t a k\u00f3dban.<\/p>\n

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

Forr\u00e1s: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u0418\u0441\u0441\u043b\u0435\u0434\u043e\u0432\u0430\u0442\u0435\u043b\u0438 \u0431\u0435\u0437\u043e\u043f\u0430\u0441\u043d\u043e\u0441\u0442\u0438 \u0438\u0437 \u043a\u043e\u043c\u043f\u0430\u043d\u0438\u0438 Qualys \u043f\u043e\u043a\u0430\u0437\u0430\u043b\u0438 \u0432\u043e\u0437\u043c\u043e\u0436\u043d\u043e\u0441\u0442\u044c \u044d\u043a\u0441\u043f\u043b\u0443\u0430\u0442\u0430\u0446\u0438\u0438 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438 \u0432 \u043f\u043e\u0447\u0442\u043e\u0432\u043e\u043c \u0441\u0435\u0440\u0432\u0435\u0440\u0435 qmail, \u0438\u0437\u0432\u0435\u0441\u0442\u043d\u043e\u0439 \u0435\u0449\u0451 \u0441 2005 \u0433\u043e\u0434\u0430 (CVE-2005-1513), \u043d\u043e \u043e\u0441\u0442\u0430\u0432\u0430\u0432\u0448\u0435\u0439\u0441\u044f \u043d\u0435\u0438\u0441\u043f\u0440\u0430\u0432\u043b\u0435\u043d\u043d\u043e\u0439, \u0442\u0430\u043a \u043a\u0430\u043a \u0430\u0432\u0442\u043e\u0440 qmail 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