{"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\/cs\/blog\/news\/uyazvimosti-v-pam-i-libblockdev-pozvolyayushhie-poluchit-prava-root-v-sisteme","title":{"rendered":"Zranitelnosti v PAM a libblockdev, kter\u00e9 umo\u017e\u0148uj\u00ed z\u00edskat pr\u00e1va root v syst\u00e9mu","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Spole\u010dnost Qualys objevila zranitelnost (CVE-2025-6019) v knihovn\u011b libblockdev, kter\u00e1 umo\u017e\u0148uje z\u00edskat pr\u00e1va root v syst\u00e9mu manipulacemi s pozad\u00edm procesu udisks. Pr\u00e1ce prototypu exploitace byla demonstrov\u00e1na na Ubuntu, Debianu, Fedo\u0159e a openSUSE Leap 15. <\/p>\n

Proces udisks se pou\u017e\u00edv\u00e1 prakticky ve v\u0161ech distribuc\u00edch Linuxu a poskytuje rozhran\u00ed D-Bus pro prov\u00e1d\u011bn\u00ed operac\u00ed se skladovac\u00edmi za\u0159\u00edzen\u00edmi, jako je p\u0159ipojov\u00e1n\u00ed a form\u00e1tov\u00e1n\u00ed. Pro prov\u00e1d\u011bn\u00ed operac\u00ed se skladovac\u00edmi za\u0159\u00edzen\u00edmi udisks vol\u00e1 funkce knihovny libblockdev. P\u0159\u00edstup k udisks je ve v\u00fdchoz\u00edm nastaven\u00ed povolen pouze u\u017eivatel\u016fm pracuj\u00edc\u00edm v kontextu «allow_active», tj. t\u011bm, kte\u0159\u00ed maj\u00ed fyzick\u00fd p\u0159\u00edstup k po\u010d\u00edta\u010di a p\u0159ipojili se prost\u0159ednictv\u00edm lok\u00e1ln\u00ed konzole nebo spustili grafickou relaci. U\u017eivatel\u00e9 p\u0159ipojuj\u00edc\u00ed se na d\u00e1lku, nap\u0159\u00edklad p\u0159es ssh, nespadnou do tohoto kontextu a nemohou p\u0159\u00edmo vyu\u017e\u00edt zranitelnost. <\/p>\n

Pro obch\u00e1zen\u00ed tohoto omezen\u00ed lze pou\u017e\u00edt trik, kter\u00fd umo\u017e\u0148uje zv\u00fd\u0161it \u00farove\u0148 ov\u011b\u0159ov\u00e1n\u00ed na «allow_active» pomoc\u00ed manipulace se spu\u0161t\u011bn\u00edm u\u017eivatelsk\u00e9 slu\u017eby systemctl, kterou polkitd vyhodnot\u00ed jako zn\u00e1mku m\u00edstn\u00ed relace. Podstatou metody je, \u017ee polkitd ur\u010duje p\u0159\u00edtomnost fyzick\u00e9ho p\u0159\u00edstupu a p\u0159i\u0159azuje \u00farove\u0148 «allow_active» na z\u00e1klad\u011b nep\u0159\u00edm\u00fdch znak\u016f, na kter\u00e9 lze m\u00edt vliv. Omezen\u00ed metody spo\u010d\u00edv\u00e1 v tom, \u017ee pro oklam\u00e1n\u00ed polkitd je nutn\u00e9, aby v syst\u00e9mu ji\u017e byla aktivn\u00ed relace m\u00edstn\u00edho u\u017eivatele s fyzick\u00fdm p\u0159\u00edstupem. <\/p>\n

Druh\u00fdm zp\u016fsobem, jak z\u00edskat pr\u00e1va «allow_active», je exploitace zranitelnosti (CVE-2025-6018) v PAM (Pluggable Authentication Modules), kterou v\u00fdzkumn\u00edci ze spole\u010dnosti Qualys odhalili b\u011bhem anal\u00fdzy zranitelnosti v libblockdev. Tato zranitelnost umo\u017e\u0148uje jak\u00e9mukoli u\u017eivateli, v\u010detn\u011b t\u011bch p\u0159ipojen\u00fdch p\u0159es SSH, vykon\u00e1vat operace v kontextu «allow_active». Probl\u00e9m je specifick\u00fd pro nastaven\u00ed PAM v openSUSE Leap 15 a SUSE Linux Enterprise 15 a projevuje se pouze v t\u011bchto distribuc\u00edch. <\/p>\n

V modulu pam_env v openSUSE a SUSE je ve v\u00fdchoz\u00edm nastaven\u00ed povoleno \u010dten\u00ed souboru ~\/.pam_environment. P\u0159es tento soubor m\u016f\u017ee u\u017eivatel nastavit prom\u011bnn\u00e9 prost\u0159ed\u00ed XDG_SEAT=seat0 a XDG_VTNR=1, kter\u00e9 budou p\u0159i dal\u0161\u00edm zpracov\u00e1n\u00ed vn\u00edm\u00e1ny jako zn\u00e1mka fyzick\u00e9 p\u0159\u00edtomnosti u\u017eivatele, i kdy\u017e bylo p\u0159ihl\u00e1\u0161en\u00ed provedeno p\u0159es SSH. Modul pam_env je tak\u00e9 vyvol\u00e1n p\u0159i p\u0159ipojov\u00e1n\u00ed p\u0159es ssh v Debianu 12 a Ubuntu 24.04 (v Debianu 13 a Ubuntu 24.10+ je deaktivov\u00e1n), ale nastaven\u00ed prom\u011bnn\u00fdch prost\u0159ed\u00ed v t\u011bchto distribuc\u00edch nem\u016f\u017ee b\u00fdt pou\u017eito pro zv\u00fd\u0161en\u00ed \u00farovn\u011b p\u0159\u00edstupu na 'allow_active', proto\u017ee pam_env je vyvol\u00e1n v kone\u010dn\u00e9 f\u00e1zi po na\u010dten\u00ed modulu pam_systemd a nastaven\u00e9 prom\u011bnn\u00e9 prost\u0159ed\u00ed nemohou ovlivnit parametry relace. <\/p>\n

Pokud jde o zranitelnost v libblockdev, \u00fato\u010dn\u00edk m\u016f\u017ee p\u0159ipojit obraz libovoln\u00e9ho souborov\u00e9ho syst\u00e9mu v loop-re\u017eimu, um\u00edst\u011bn\u00edm v tomto obraze spustiteln\u00e9ho souboru s p\u0159\u00edznakem SUID root nebo speci\u00e1ln\u00edho za\u0159\u00edzen\u00ed (\/dev\/mem) pro n\u00edzko\u00farov\u0148ov\u00fd p\u0159\u00edstup k disk\u016fm nebo pam\u011bti. Pro zablokov\u00e1n\u00ed takov\u00fdch \u00fatok\u016f jsou obrazy FS p\u0159ipojov\u00e1ny syst\u00e9mem s p\u0159\u00edznaky nosuid a nodev, ale zranitelnost v libblockdev umo\u017e\u0148uje p\u0159ipojit obraz bez p\u0159\u00edznak\u016f nosuid a nodev. Podstatou zranitelnosti je, \u017ee udisks umo\u017e\u0148uje u\u017eivateli s \u00farovn\u00ed p\u0159\u00edstupu 'allow_active' m\u011bnit velikosti sv\u00fdch souborov\u00fdch syst\u00e9m\u016f a libblockdev b\u011bhem t\u00e9to operace do\u010dasn\u011b p\u0159ipojuje FS bez nastaven\u00ed p\u0159\u00edznak\u016f nosuid a nodev. <\/p>\n

T\u00edmto se \u00fatok soust\u0159ed\u00ed na vytvo\u0159en\u00ed loop za\u0159\u00edzen\u00ed na z\u00e1klad\u011b obrazu FS XFS, ve kter\u00e9m je um\u00edst\u011bn soubor suid root, iniciaci operace zm\u011bny velikosti loop za\u0159\u00edzen\u00ed a sledov\u00e1n\u00ed okam\u017eiku jeho p\u0159ipojen\u00ed do adres\u00e1\u0159e \/tmp\/blockdev*: victim> killall -KILL gvfs-udisks2-volume-monitor victim> udisksctl loop-setup --file .\/xfs.image --no-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 --system --dest org.freedesktop.UDisks2 --object-path \/org\/freedesktop\/UDisks2\/block_devices\/loop0 --method 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

Zranitelnost v libblockdev byla zat\u00edm odstran\u011bna pouze ve form\u011b z\u00e1plat. Stav nov\u00e9 verze bal\u00ed\u010dku nebo p\u0159\u00edpravy opravy v distribuc\u00edch lze zkontrolovat na n\u00e1sleduj\u00edc\u00edch str\u00e1nk\u00e1ch (pokud je str\u00e1nka nedostupn\u00e1, znamen\u00e1 to, \u017ee v\u00fdvoj\u00e1\u0159i distribuce se zat\u00edm neza\u010dali zab\u00fdvat probl\u00e9mem): Debian, Ubuntu, Fedora, SUSE\/openSUSE, RHEL, Gentoo a Arch (1, 2). Jako obch\u016fdky pro zablokov\u00e1n\u00ed zranitelnosti lze zm\u011bnit pravidlo p\u0159\u00edstupu k operaci «org.freedesktop.udisks2.modify-device» v polkitu, zm\u011bnou hodnoty parametru «allow_active» na «auth_admin» v souboru \/usr\/share\/polkit-1\/actions\/org.freedesktop.UDisks2.policy. <\/p>\n

D\u00e1le lze zm\u00ednit ned\u00e1vno zve\u0159ejn\u011bnou zranitelnost (CVE-2025-6020) v bal\u00ed\u010dku linux-pam, kter\u00e1 umo\u017e\u0148uje lok\u00e1ln\u00edmu u\u017eivateli z\u00edskat pr\u00e1va root. Modul pam_namespace spr\u00e1vn\u011b neov\u011b\u0159oval cestu k soubor\u016fm ovl\u00e1dan\u00fdm u\u017eivateli, co\u017e umo\u017enilo prost\u0159ednictv\u00edm manipulace se symbolick\u00fdmi odkazy a dosa\u017een\u00edm stavu z\u00e1vodu p\u0159epsat privilegovan\u00e9 soubory v syst\u00e9mu. Zranitelnost byla opravena v vyd\u00e1n\u00ed linux-pam 1.7.1. Stav nov\u00e9 verze bal\u00ed\u010dku nebo p\u0159\u00edpravy opravy v distribuc\u00edch lze zkontrolovat na n\u00e1sleduj\u00edc\u00edch str\u00e1nk\u00e1ch: Debian, Ubuntu, Fedora, SUSE\/openSUSE, RHEL, Gentoo a Arch (1, 2).
\n
Zdroj: 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. \u041f\u0440\u043e\u0446\u0435\u0441\u0441 udisks \u043f\u0440\u0438\u043c\u0435\u043d\u044f\u0435\u0442\u0441\u044f \u043f\u0440\u0430\u043a\u0442\u0438\u0447\u0435\u0441\u043a\u0438 \u0432\u043e \u0432\u0441\u0435\u0445 \u0434\u0438\u0441\u0442\u0440\u0438\u0431\u0443\u0442\u0438\u0432\u0430\u0445 Linux \u0438 \u043f\u0440\u0435\u0434\u043e\u0441\u0442\u0430\u0432\u043b\u044f\u0435\u0442 \u0438\u043d\u0442\u0435\u0440\u0444\u0435\u0439\u0441 D-Bus \u0434\u043b\u044f \u0432\u044b\u043f\u043e\u043b\u043d\u0435\u043d\u0438\u044f \u043e\u043f\u0435\u0440\u0430\u0446\u0438\u0439 \u0441 \u043d\u0430\u043a\u043e\u043f\u0438\u0442\u0435\u043b\u044f\u043c\u0438, \u0442\u0430\u043a\u0438\u0445 \u043a\u0430\u043a \u043c\u043e\u043d\u0442\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435 \u0438 \u0444\u043e\u0440\u043c\u0430\u0442\u0438\u0440\u043e\u0432\u0430\u043d\u0438\u0435. \u0414\u043b\u044f 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