{"id":137763,"date":"2025-06-21T17:11:54","date_gmt":"2025-06-21T15:11:54","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/uyazvimosti-v-pam-i-libblockdev-pozvolyayushhie-poluchit-prava-root-v-sisteme"},"modified":"2025-06-21T17:11:54","modified_gmt":"2025-06-21T15:11:54","slug":"uyazvimosti-v-pam-i-libblockdev-pozvolyayushhie-poluchit-prava-root-v-sisteme","status":"publish","type":"post","link":"https:\/\/prohoster.info\/hr\/blog\/news\/uyazvimosti-v-pam-i-libblockdev-pozvolyayushhie-poluchit-prava-root-v-sisteme","title":{"rendered":"Ranljivosti u PAM i libblockdev, koje omogu\u0107uju sticanje root prava u sustavu","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Tvrtka Qualys otkrila je ranjivost (CVE-2025-6019) u biblioteci libblockdev, koja omogu\u0107uje dobivanje root prava u sustavu manipulacijama s pozadinskim procesom udisks. Prototip exploit-a prikazan je u Ubuntu, Debian, Fedora i openSUSE Leap 15. <\/p>\n

Proces udisks koristi se u gotovo svim Linux distribucijama i pru\u017ea D-Bus su\u010delje za izvo\u0111enje operacija s ure\u0111ajima, poput montiranja i formatiranja. Kako bi izveo radnje s ure\u0111ajima, udisks poziva funkcije knji\u017enice libblockdev. Pristup udisksu po defaultu je otvoren samo za korisnike koji rade u kontekstu \u201eallow_active\u201c, tj. onima koji imaju fizi\u010dki pristup ra\u010dunalu i koji su se povezali preko lokalne konzole ili pokrenuli grafi\u010dku sesiju. Korisnici koji se povezuju udaljeno, primjerice putem ssh, ne ulaze u ovaj kontekst i ne mogu izravno iskoristiti ranjivost. <\/p>\n

Za zaobila\u017eenje tog ograni\u010denja mo\u017ee se upotrijebiti trik koji omogu\u0107uje podizanje razine autentifikacije na \u201eallow_active\u201c manipulacijom pokretanjem korisni\u010dke usluge uz pomo\u0107 alata systemctl, koju \u0107e polkitd prepoznati kao znak lokalne sesije. Bit metode je u tome da polkitd utvr\u0111uje postojanje fizi\u010dkog pristupa i dodjeljuje razinu \u201eallow_active\u201c temeljem posrednih znakova na koje se mo\u017ee utjecati. Ograni\u010denje metode je \u0161to je za prevaru polkitda potrebno da u sustavu ve\u0107 postoji aktivna sesija lokalnog korisnika s fizi\u010dkim pristupom. <\/p>\n

Druga metoda stjecanja prava \u201eallow_active\u201c je iskori\u0161tavanje ranjivosti (CVE-2025-6018) u PAM (Pluggable Authentication Modules), koju su istra\u017eiva\u010di iz Qualys-a otkrili tijekom analize ranjivosti u libblockdev. Ranjivost omogu\u0107ava bilo kojem korisniku, uklju\u010duju\u0107i onog koji se povezao putem SSH, izvo\u0111enje operacija u kontekstu \u201eallow_active\u201c. Problem je specifi\u010dan za PAM postavke u openSUSE Leap 15 i SUSE Linux Enterprise 15, i pojavljuje se samo u tim distribucijama. <\/p>\n

U modulu pam_env u openSUSE i SUSE prema zadanim postavkama uklju\u010deno je \u010ditanje datoteke ~\/.pam_environment. Kroz ovu datoteku korisnik mo\u017ee postaviti varijable okru\u017eenja XDG_SEAT=seat0 i XDG_VTNR=1, koje \u0107e biti percipirane kao znak fizi\u010dke prisutnosti korisnika, \u010dak i ako se zapravo prijavio putem SSH. Modul pam_env tako\u0111er se poziva prilikom povezivanja putem ssh u Debian 12 i Ubuntu 24.04 (u Debian 13 i Ubuntu 24.10+ je isklju\u010den), ali postavljanje varijabli okru\u017eenja u tim distribucijama ne mo\u017ee se koristiti za pove\u0107anje razine pristupa do 'allow_active', jer se pam_env poziva na kona\u010dnom stadiju nakon u\u010ditavanja modula pam_systemd i postavljene varijable okru\u017eenja ne mogu utjecati na parametre sesije. <\/p>\n

\u0160to se ti\u010de ranjivosti u libblockdev, napada\u010d mo\u017ee montirati sliku proizvoljnog datote\u010dnog sustava u loop-re\u017eimu, smje\u0161taju\u0107i u tu sliku izvr\u0161nu datoteku s SUID root zastavicom ili posebnim ure\u0111ajem (\/dev\/mem) za niskorazinski pristup diskovima ili memoriji. Kako bi se blokirali takvi napadi, F\u0421 slike montiraju se sustavom s zastavama nosuid i nodev, ali ranjivost u libblockdev omogu\u0107ava montiranje slike bez zastava nosuid i nodev. Su\u0161tina ranjivosti je u tome \u0161to udisks korisniku s razinom pristupa 'allow_active' omogu\u0107ava promjenu veli\u010dine vlastitih datote\u010dnih sustava, a libblockdev tijekom izvo\u0111enja te operacije privremeno montira F\u0421 bez postavljanja zastava nosuid i nodev. <\/p>\n

Tako se napad svodi na stvaranje loop-ure\u0111aja temeljenog na slici F\u0421 XFS u kojoj se nalazi suid root datoteka, iniciranje operacije promjene veli\u010dine loop-ure\u0111aja i pra\u0107enje trenutka njegovog montiranja u katalog \/tmp\/blockdev*: victim> killall -KILL gvfs-udisks2-volume-monitor victim> udisksctl loop-setup \u2014file .\/xfs.image \u2014no-user-interaction Mapped file .\/xfs.image as \/dev\/loop0. victim> while true; do \/tmp\/blockdev*\/bash -c 'sleep 10; ls -l \/tmp\/blockdev*\/bash' && break; done 2>\/dev\/null & victim> gdbus call \u2014system \u2014dest org.freedesktop.UDisks2 \u2014object-path \/org\/freedesktop\/UDisks2\/block_devices\/loop0 \u2014method org.freedesktop.UDisks2.Filesystem.Resize 0 '{}' Error: GDBus.Error:org.freedesktop.UDisks2.Error.Failed: Error resizing filesystem on \/dev\/loop0: Failed to unmount '\/dev\/loop0' after resizing it: target is busy -r-sr-xr-x. 1 root root 1406608 Jun 18 09:42 \/tmp\/blockdev.RSM429\/bash victim> \/tmp\/blockdev*\/bash -p victim# id uid=65534(nobody) gid=65534(nobody) euid=0(root) groups=65534(nobody) <\/p>\n

Ranljivost u libblockdev trenutno je ispravljena samo putem ispravki. Stanje nove verzije paketa ili priprema ispravke u distribucijama mogu se provjeriti na sljede\u0107im stranicama (ako stranica nije dostupna, to zna\u010di da se programeri distribucije jo\u0161 nisu posvetili rje\u0161avanju problema): Debian, Ubuntu, Fedora, SUSE\/openSUSE, RHEL, Gentoo i Arch (1, 2). Kao zaobilazno rje\u0161enje za blokiranje ranjivosti, mogu\u0107e je promijeniti pravilo pristupa operaciji «org.freedesktop.udisks2.modify-device» u polkit, izmjenom vrijednosti parametra «allow_active» u datoteci \/usr\/share\/polkit-1\/actions\/org.freedesktop.UDisks2.policy s «yes» na «auth_admin». <\/p>\n

Dodatno se mo\u017ee napomenuti ranjivost (CVE-2025-6020) otkrivenu prije nekoliko sati u paketu linux-pam, koja omogu\u0107uje lokalnom korisniku da dobije root prava. Modul pam_namespace ispravno nije provjeravao putanje datoteka pod kontrolom korisnika, \u0161to je omogu\u0107ilo manipulacijom simboli\u010dnim vezama i postizanjem stanja utrke da do\u0111e do prepisivanja privilegiranih datoteka u sustavu. Ranjivost je ispravljena u izdanju linux-pam 1.7.1. Status nove verzije paketa ili pripremu ispravka u distribucijama mo\u017ee se provjeriti na sljede\u0107im stranicama: Debian, Ubuntu, Fedora, SUSE\/openSUSE, RHEL, Gentoo i Arch (1, 2).
\n
Izvor: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

\u041a\u043e\u043c\u043f\u0430\u043d\u0438\u044f Qualys \u0432\u044b\u044f\u0432\u0438\u043b\u0430 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u044c (CVE-2025-6019) \u0432 \u0431\u0438\u0431\u043b\u0438\u043e\u0442\u0435\u043a\u0435 libblockdev, \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0443\u044e \u0447\u0435\u0440\u0435\u0437 \u043c\u0430\u043d\u0438\u043f\u0443\u043b\u044f\u0446\u0438\u0438 \u0441 \u0444\u043e\u043d\u043e\u0432\u044b\u043c \u043f\u0440\u043e\u0446\u0435\u0441\u0441\u043e\u043c udisks \u043f\u043e\u043b\u0443\u0447\u0438\u0442\u044c \u043f\u0440\u0430\u0432\u0430 root \u0432 \u0441\u0438\u0441\u0442\u0435\u043c\u0435. \u0420\u0430\u0431\u043e\u0442\u0430 \u043f\u0440\u043e\u0442\u043e\u0442\u0438\u043f\u0430 \u044d\u043a\u0441\u043f\u043b\u043e\u0438\u0442\u0430 \u043f\u0440\u043e\u0434\u0435\u043c\u043e\u043d\u0441\u0442\u0440\u0438\u0440\u043e\u0432\u0430\u043d\u0430 \u0432 Ubuntu, Debian, Fedora \u0438 openSUSE Leap 15. 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