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CVE-2026-78409— Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks

Quick assessment

Affected
Red Hat Red Hat Enterprise Linux 10
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Linux 6.15 及更高版本中， 选项使用了一个针对已分离树（detached-tree）的快速路径，并将配置好的子目录传递给 函数，同时使用了 标志。然而，该标志并不能阻止中间符号链接的遍历，也无法确保路径解析始终保留在新挂载的文件系统内部。因此，拥有 中授权的 条目的本地非特权用户，能够将主机的某个路径挂载到预期的挂载点（mountpoint）上。

CVSS 7.0 · High

Possible ATT&CK Techniques 1 AI

T1078 · Valid Accounts
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I. Basic Information for CVE-2026-78409

Vulnerability Information
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Vulnerability Title
Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks
Source: CVE Program / CVE List V5
Vulnerability Description
The X-mount.subdir option uses a detached-tree fast path on Linux 6.15 and later and passes the configured subdirectory to open_tree() with AT_SYMLINK_NOFOLLOW. That flag does not stop intermediate symlink traversal or keep resolution inside the newly mounted filesystem. A local unprivileged user with an fstab-authorized X-mount.subdir entry can attach a host path at the intended mountpoint.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
在文件访问前对链接解析不恰当(链接跟随)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Red Hat Red Hat Enterprise Linux 10 - cpe:/o:redhat:enterprise_linux:10
Red Hat Red Hat Enterprise Linux 7 - cpe:/o:redhat:enterprise_linux:7
Red Hat Red Hat Enterprise Linux 8 - cpe:/o:redhat:enterprise_linux:8
Red Hat Red Hat Enterprise Linux 9 - cpe:/o:redhat:enterprise_linux:9
Red Hat Red Hat Enterprise Linux 9 - cpe:/o:redhat:enterprise_linux:9
Red Hat Red Hat Enterprise Linux 9 - cpe:/o:redhat:enterprise_linux:9
Red Hat Red Hat Hardened Images - cpe:/a:redhat:hummingbird:1
Red Hat Red Hat OpenShift Container Platform 4 - cpe:/a:redhat:openshift:4

II. Public POCs for CVE-2026-78409

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III. Intelligence Information for CVE-2026-78409

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Vendor Advisories for CVE-2026-78409 (2)

Other References for CVE-2026-78409 (1)

Same Patch Batch · Red Hat · 2026-09-02 · 7 CVEs total

CVE-2026-78408 7.9 HIGH Util-linux: util-linux: nsenter --join-cgroup leaks root cgroup migration authority
CVE-2026-84838 7.8 HIGH Rpm: command injection in rpmuncompress via unescaped filenames passed to popen()
CVE-2026-84837 7.8 HIGH Rpm: command injection in `rpmbuild -t*` (`gettarspec`) via unescaped tarball path
CVE-2026-78410 7.8 HIGH Util-linux: util-linux: restricted bind mounts do not pin the source, allowing x-mount.own
CVE-2026-82968 6.4 MEDIUM Keycloak-services: keycloak-services: cross-session email verification proof not bound to
CVE-2026-53683 4.3 MEDIUM Freeipa: idm: idm/freeipa web ui - client-side open redirect in reset_password.html

IV. Related Vulnerabilities

Same product: Red Hat Enterprise Linux 10
Same vendor: Red Hat
Same weakness: CWE-59

V. Comments for CVE-2026-78409

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