# CVE-2026-98977: namespace: handle mount locking for automounts correctly


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** AZL-110804, BELL-CVE-2026-98977, DEBIAN-CVE-2026-98977, GHSA-qrj7-g2h3-853j, UBUNTU-CVE-2026-98977

## What is CVE-2026-98977?

CVE-2026-98977 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

namespace: handle mount locking for automounts correctly

If mounts are propagated across user namespaces, attach_recursive_mnt()
locks every copy of the source mount to protect overmounts from
vanishing and revealing the underlying files or directories.

The user namespace is taken from the caller's mount namespaces since
this is where the mounts end up. Except, that's not always true.
Automounts may legitimately get popped in by tasks located in a
different mount and user namespace during path lookup.

Then check doesn't make sense at that point. The copy in the namespace
of the parent - which may be the host's - is now locked and the host
cannot change the flags of its own mounts anymore.

Here's the reproducer:

- host has debugfs mounted nosuid,nodev,noexec and shared
- tracefs automount below it is not yet active
- hand a child process a directory descriptor on that mount
- child process enters auser and mount namespace
- child process' namespace now holds a locked copy of the host's debugfs
  mount that receives propagation from it
- child process stats "tracing/." through the descriptor
- lookup runs on the host's mount so the automount lands below the host's mount
- propagation puts a copy below the child's copy
- both try to clear the flags on the mount they got, with a bind remount:

    host, on its own automount:            MS_REMOUNT|MS_BIND = EPERM
    child, on the copy in its namespace:   MS_REMOUNT|MS_BIND = 0

So the lock landed on the host's mount instead of the child's copy.
Congrats. So we need to compare with the owner of the namespace the
mount actually gets mounted on. For all regular cases that is the
caller's mount namespace and so nothing changes.

Detached trees in anonymous mount namespaces by be handed over via
SCM_RIGHTS or inherited in other ways on purpose so the attaching task's
mount namespace is authoritative, not the creator of the detached tree.

## Which versions are affected by CVE-2026-98977?


## How do I fix CVE-2026-98977?

Upgrade to a fixed version.

## Is CVE-2026-98977 being exploited?

There is no known exploitation of CVE-2026-98977 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98977 and fix it if it is affected.

What it is: CVE-2026-98977 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98977 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-2026-98977/ (Markdown: https://insights.sbomify.com/CVE-2026-98977/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98977
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98977
- OSV: https://osv.dev/vulnerability/CVE-2026-98977

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98977/
Summaries are generated and may contain mistakes; the official description above is the record.