# CVE-2026-98978: namespace: never expire a locked mount

CVE-2026-98978 is fixed in linux on 1 platform by DEBIAN-CVE-2026-98978 (version 7.2.11-1), released October 24, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-98978
- Priority: High
- CVSS: 8.4 (Important)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 23, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98978

## Description

In the Linux kernel, the following vulnerability has been resolved:  namespace: never expire a locked mount  Locked mounts are special. They protect the underlying files and directories from being revealed. do_umount() refuses to unmount locked mounts but shrink_submounts() doesn't.  A shrinkable mount can become locked once the owner of a user namespace puts it beneath a locked mount with MOVE_MOUNT_BENEATH. The locked property now moves to the mount at the bottom making it possible to unmount the top mount.  So umount() of an unlocked ancestor now expires the bottom mount first and the covered directory is revealed:    move_mount(c -> x/hidden, MOVE_MOUNT_BENEATH) = 0   the cover after the lock moved:  umount2(x/hidden) = 0   the holder of the lock:          umount2(x/hidden) = EINVAL   the root of the copy, busy:      umount2(x) = EBUSY   reads x/hidden/secret: "covered-by-root"  So leave a locked mount alone as it dies together with its parent. A plain umount() of an unlocked mount with a locked one below it is EBUSY from now on. It's the same for any other locked child. A lazy umount still takes the whole tree.  mark_mounts_for_expiry() never sees a locked mount. lock_mnt_tree() leaves a mount on an expiry list alone and nothing else puts a locked one on such a list. Add an assert for this.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.2.11-1 | [DEBIAN-CVE-2026-98978](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98978.md) | Oct 24, 2026 |

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