High [CVE-2026-78409] Util-linux: util-linux: x-mount.subdir detached-tree resolution can escape via intermediate symlinks
This high-severity Red Hat Linux advisory covers CVE-2026-78409 affecting Red Hat Hardened Images.
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Summary
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. Affected versions: util-linux v2.42 through v2.42.2.
Earlier releases, including v2.40 and v2.41, are not affected. Restricted-user SUID mount(8) reproduction also requires Linux >= 6.15.
Fixed in v2.41.6 and v2.42.3. Red Hat severity: Important — CVSS 7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H).
Weakness: CWE-59. Affected Red Hat products: Red Hat Hardened Images.
Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9; Red Hat OpenShift Container Platform 4 as not affected. Red Hat does not currently list a fixing RHSA for this CVE.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Mitigation checklist
- Upgrade to util-linux v2.41.6, v2.42.3, or later. Until a fix is applied, do not allow unprivileged /etc/fstab entries that specify X-mount.subdir.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
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