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Response snapshot Oct 27, 2026, 01:44 UTC

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VulnerabilityCVE-2026-98978

Linux kernel: namespace: never expire a locked mount

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.

At a glance

Exploited
Not known
Severity
8.4 High (CVSS 3.1)
Chance of exploitation
0.2% in the next 30 days
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-98978 (opens a new tab)

What happened

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.

Continue reading

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.

Scores and how they were measured

CVSS base severity

8.4

Version 3.1As of

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.2%

Scored Percentile 6.3%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2026-98978 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-98978, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 24). Linux kernel: namespace: never expire a locked mount (CVE-2026-98978). https://kevwire.com/record/CVE-2026-98978

MLA

"Linux kernel: namespace: never expire a locked mount (CVE-2026-98978)." KEVWire, 24 Oct. 2026, kevwire.com/record/CVE-2026-98978.

Chicago

KEVWire. "Linux kernel: namespace: never expire a locked mount (CVE-2026-98978)." Last modified October 24, 2026. https://kevwire.com/record/CVE-2026-98978.

Evidence summary (plain text)

Linux kernel: namespace: never expire a locked mount (Oct 23, 2026).
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.
CVSS 8.4 (version 3.1; evidence as of Oct 24, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-98978).
EPSS 0.2% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-98978&date=2026-10-26).
Sources:
NVD CVE-2026-98978: https://nvd.nist.gov/vuln/detail/CVE-2026-98978
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=9000
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-98978&date=2026-10-26
Record ID: CVE-2026-98978.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 01:40 UTC. Ingestion is not an independent editorial investigation.

NVD status: Received. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

Record detail