Описание
util-linux is a random collection of Linux utilities. Prior to version 2.41.4, a TOCTOU (Time-of-Check-Time-of-Use) vulnerability has been identified in the SUID binary /usr/bin/mount from util-linux. The mount binary, when setting up loop devices, validates the source file path with user privileges via fork() + setuid() + realpath(), but subsequently re-canonicalizes and opens it with root privileges (euid=0) without verifying that the path has not been replaced between both operations. Neither O_NOFOLLOW, nor inode comparison, nor post-open fstat() are employed. This allows a local unprivileged user to replace the source file with a symlink pointing to any root-owned file or device during the race window, causing the SUID binary to open and mount it as root. Exploitation requires an /etc/fstab entry with user,loop options whose path points to a directory where the attacker has write permission, and that /usr/bin/mount has the SUID bit set (the default configuration on virtually all Linux distributions). The impact is unauthorized read access to root-protected files and block devices, including backup images, disk volumes, and any file containing a valid filesystem. This issue has been patched in version 2.41.4.
A flaw was found in util-linux. When an /etc/fstab entry is configured with the user,loop options, the mount program checks the file path with user permissions but later opens it with root privileges. This creates a brief Time-of-Check-Time-of-Use (TOCTOU) window where an attacker can substitute the intended file with a malicious symbolic link. This allows a local unprivileged user to mount any root-owned file or block device that contains a valid filesystem, gaining full read access to its contents.
Отчет
This vulnerability is only exploitable when an /etc/fstab entry exists with user,loop options and its source path points to a directory where the attacker has write permission (e.g., the user's home directory). Also, this issue allows an attacker to mount any root-owned file or block device containing a valid filesystem, causing information disclosure. There is no memory corruption or arbitrary code execution. Due to these reasons, this flaw has been rated with a moderate severity.
Меры по смягчению последствий
To mitigate this flaw, remove the 'user' option from any loop mounts in the /etc/fstab file or ensure the the source path points to a root-owned directory where unprivileged users do not have write permissions.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | util-linux | Fix deferred | ||
| Red Hat Enterprise Linux 6 | util-linux-ng | Not affected | ||
| Red Hat Enterprise Linux 7 | util-linux | Not affected | ||
| Red Hat Enterprise Linux 8 | util-linux | Fix deferred | ||
| Red Hat Enterprise Linux 9 | util-linux | Fix deferred | ||
| Red Hat OpenShift Container Platform 4 | rhcos | Fix deferred | ||
| Red Hat Hardened Images | util-linux-main-2.42-7.1.hum1 | Fixed | RHSA-2026:7180 | 09.04.2026 |
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Ссылки на источники
Дополнительная информация
Статус:
EPSS
4.7 Medium
CVSS3
Связанные уязвимости
util-linux is a random collection of Linux utilities. Prior to version 2.41.4, a TOCTOU (Time-of-Check-Time-of-Use) vulnerability has been identified in the SUID binary /usr/bin/mount from util-linux. The mount binary, when setting up loop devices, validates the source file path with user privileges via fork() + setuid() + realpath(), but subsequently re-canonicalizes and opens it with root privileges (euid=0) without verifying that the path has not been replaced between both operations. Neither O_NOFOLLOW, nor inode comparison, nor post-open fstat() are employed. This allows a local unprivileged user to replace the source file with a symlink pointing to any root-owned file or device during the race window, causing the SUID binary to open and mount it as root. Exploitation requires an /etc/fstab entry with user,loop options whose path points to a directory where the attacker has write permission, and that /usr/bin/mount has the SUID bit set (the default configuration on virtually al...
util-linux is a random collection of Linux utilities. Prior to version 2.41.4, a TOCTOU (Time-of-Check-Time-of-Use) vulnerability has been identified in the SUID binary /usr/bin/mount from util-linux. The mount binary, when setting up loop devices, validates the source file path with user privileges via fork() + setuid() + realpath(), but subsequently re-canonicalizes and opens it with root privileges (euid=0) without verifying that the path has not been replaced between both operations. Neither O_NOFOLLOW, nor inode comparison, nor post-open fstat() are employed. This allows a local unprivileged user to replace the source file with a symlink pointing to any root-owned file or device during the race window, causing the SUID binary to open and mount it as root. Exploitation requires an /etc/fstab entry with user,loop options whose path points to a directory where the attacker has write permission, and that /usr/bin/mount has the SUID bit set (the default configuration on virtually all L
util-linux: TOCTOU Race Condition in util-linux mount(8) - Loop Device Setup
util-linux is a random collection of Linux utilities. Prior to version ...
EPSS
4.7 Medium
CVSS3