# CVE-2026-98988: namespace: keep covered mounts covered in OPEN_TREE_NAMESPACE


- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 24 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98988, GHSA-6v5x-qw46-2jph, UBUNTU-CVE-2026-98988

## What is CVE-2026-98988?

CVE-2026-98988 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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.

## Which versions are affected by CVE-2026-98988?


## How do I fix CVE-2026-98988?

Upgrade to a fixed version.

## Is CVE-2026-98988 being exploited?

There is no known exploitation of CVE-2026-98988 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98988 and fix it if it is affected.

What it is: CVE-2026-98988 is a high-severity vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98988 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98988/ (Markdown: https://insights.sbomify.com/CVE-2026-98988/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98988
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98988
- OSV: https://osv.dev/vulnerability/CVE-2026-98988

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98988/
Summaries are generated and may contain mistakes; the official description above is the record.