KEVWire

Security intelligence, with context.

Response snapshot Oct 27, 2026, 05:48 UTC

Back to the wire
Permalink
VulnerabilityCVE-2026-98988

Linux kernel: namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE

In the Linux kernel, the following vulnerability has been resolved: namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE open_tree(OPEN_TREE_NAMESPACE) creates a new mount namespace from a copy of the tree at the given path.

Published Updated

At a glance

Exploited
Not known
Severity
8.8 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-2026-98988 (opens a new tab)

What happened

In the Linux kernel, the following vulnerability has been resolved:

namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE

open_tree(OPEN_TREE_NAMESPACE) creates a new mount namespace from a copy of the tree at the given path. The caller needs to be privileged over its current user namespace because the new mount namespace will be owned by it. It doesn't need to be privileged over the mount namespace the tree is copied from. An unprivileged user just needs to create a user namespace first.

The copy follows the rules of a detached bind mount. Without AT_RECURSIVE only the mount itself is cloned and its children are left out. With AT_RECURSIVE unbindable mounts are skipped. Both is fine when the caller has privileges over the source mount namespace because it could unmount those mounts anyway. Not so for an unprivileged user in that mount namespace.

Continue reading

For them a mount namespace copy is what unshare() does. copy_mnt_ns() copies everything including unbindable mounts and lock_mnt_tree() makes sure nothing can be unmounted in the copy. Nothing that was covered gets revealed.

create_new_namespace() only does the locking and so the covered content is right there in the new mount namespace:

# mount -t tmpfs none /tmp/otn; mkdir /tmp/otn/covered # echo hidden > /tmp/otn/covered/under.txt # mount -t tmpfs none /tmp/otn/covered

uid 1000, after unshare(CLONE_NEWUSER): fd = open_tree(AT_FDCWD, "/tmp/otn", OPEN_TREE_NAMESPACE); setns(fd, CLONE_NEWNS); open("/covered/under.txt", O_RDONLY) -> "hidden"

Covering paths with mounts is how container runtimes mask parts of /proc and /sys and how admins hide things.

When the caller's user namespace doesn't own the source mount namespace copy the way unshare() does and refuse a non-recursive copy of a mount that has anything mounted below the requested directory and copy unbindable mounts in a recursive copy. A caller that is privileged over the source mount namespace sees no change.

Scores and how they were measured

CVSS base severity

8.8

Version 3.1As of

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

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 5.6%

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-2026-98988 (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-2026-98988, 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: keep covered mounts covered in OPEN_TREE_NAMESPACE (CVE-2026-98988). https://kevwire.com/record/CVE-2026-98988

MLA

"Linux kernel: namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE (CVE-2026-98988)." KEVWire, 24 Oct. 2026, kevwire.com/record/CVE-2026-98988.

Chicago

KEVWire. "Linux kernel: namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE (CVE-2026-98988)." Last modified October 24, 2026. https://kevwire.com/record/CVE-2026-98988.

Evidence summary (plain text)

Linux kernel: namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE (Oct 23, 2026).
In the Linux kernel, the following vulnerability has been resolved:

namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE

open_tree(OPEN_TREE_NAMESPACE) creates a new mount namespace from a
copy of the tree at the given path. The caller needs to be privileged
over its current user namespace because the new mount namespace will be
owned by it. It doesn't need to be privileged over the mount namespace
the tree is copied from. An unprivileged user just needs to create a
user namespace first.

The copy follows the rules of a detached bind mount. Without
AT_RECURSIVE only the mount itself is cloned and its children are left
out. With AT_RECURSIVE unbindable mounts are skipped. Both is fine when
the caller has privileges over the source mount namespace because it
could unmount those mounts anyway. Not so for an unprivileged user in
that mount namespace. For them a mount namespace copy is what unshare()
does. copy_mnt_ns() copies everything including unbindable mounts and
lock_mnt_tree() makes sure nothing can be unmounted in the copy. Nothing
that was covered gets revealed.

create_new_namespace() only does the locking and so the covered content
is right there in the new mount namespace:

  # mount -t tmpfs none /tmp/otn; mkdir /tmp/otn/covered
  # echo hidden > /tmp/otn/covered/under.txt
  # mount -t tmpfs none /tmp/otn/covered

  uid 1000, after unshare(CLONE_NEWUSER):
  fd = open_tree(AT_FDCWD, "/tmp/otn", OPEN_TREE_NAMESPACE);
  setns(fd, CLONE_NEWNS);
  open("/covered/under.txt", O_RDONLY)  -> "hidden"

Covering paths with mounts is how container runtimes mask parts of
/proc and /sys and how admins hide things.

When the caller's user namespace doesn't own the source mount namespace
copy the way unshare() does and refuse a non-recursive copy of a mount
that has anything mounted below the requested directory and copy
unbindable mounts in a recursive copy. A caller that is privileged over
the source mount namespace sees no change.
CVSS 8.8 (version 3.1; evidence as of Oct 24, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-98988).
EPSS 0.2% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-98988&date=2026-10-26).
Sources:
NVD CVE-2026-98988: https://nvd.nist.gov/vuln/detail/CVE-2026-98988
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-2026-98988&date=2026-10-26
Record ID: CVE-2026-98988.
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.

Record JSON

Your account

Email alerts

Email alerts are not available yet. To follow your stack today, use its RSS feed, which honors your filters, or connect an AI agent through the API.

Suggest an improvement

Ideas, missing sources, corrections, and bugs are all welcome. No account needed. Suggestions are reviewed by a person before anything changes.

Record details

Record detail