# CVE-2026-98990: namespace: check a submount for references right before unmounting it


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** AZL-110828, BELL-CVE-2026-98990, DEBIAN-CVE-2026-98990, GHSA-5v88-6pxr-8v5g, UBUNTU-CVE-2026-98990

## What is CVE-2026-98990?

CVE-2026-98990 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

namespace: check a submount for references right before unmounting it

shrink_submounts() and mark_mounts_for_expiry() first collect all the
mounts they are allowed to unmount and then unmount them.

Whether a mount is busy is decided by propagate_mount_busy() on the
tree. But unmounting the first mount changes the tree that the second
one propagates into. propagate_umount()
moves a surviving overmount off a copy it unmounts and mounts it where
the copy was mounted. If that's where the propagated copy of the second
victim is looked up the overmount becomes a candidate of the second
umount_tree(). It's childless and so trim_one() commits it without
looking at its reference count.

So a synchronous umount pulls out a busy mount that is in use somewhere
else and marks it MNT_SYNC_UMOUNT while it has users:

  umount2(/tmp/plshrink/p1, 0) = 0 errno 0
  cwd is (unreachable)

The same two umounts requested one after the other fail with EBUSY.
This needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of
NFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts
inherit the flag.

Check each mount right before it is unmounted under the same hold of
namespace_sem and mount_lock as the umount itself. Make sure that the
algorithm stays linear.

## Which versions are affected by CVE-2026-98990?


## How do I fix CVE-2026-98990?

Upgrade to a fixed version.

## Is CVE-2026-98990 being exploited?

There is no known exploitation of CVE-2026-98990 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98990 and fix it if it is affected.

What it is: CVE-2026-98990 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98990 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-2026-98990/ (Markdown: https://insights.sbomify.com/CVE-2026-98990/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98990
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98990
- OSV: https://osv.dev/vulnerability/CVE-2026-98990

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98990/
Summaries are generated and may contain mistakes; the official description above is the record.