# CVE-2026-72034: fhandle: reject detached mounts in capable_wrt_mount()

> A race condition in the Linux kernel fhandle subsystem can cause a null pointer dereference and system panic when handling detached mounts.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-72034, DEBIAN-CVE-2026-72034, GHSA-g7v4-chcg-vj96, UBUNTU-CVE-2026-72034

## What is CVE-2026-72034?

CVE-2026-72034 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

fhandle: reject detached mounts in capable_wrt_mount()

The recent fhandle RCU fix moved the mount namespace capability check
into capable_wrt_mount(), so a non-NULL mnt_namespace survives the
ns_capable() dereference. The helper still assumes the later
READ_ONCE(mount->mnt_ns) must be non-NULL because may_decode_fh()
checked is_mounted() first.

That assumption is not stable. A detached mount from
open_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while
open_by_handle_at() is between those checks, and umount_tree() can
clear mount->mnt_ns. If the helper observes NULL, it dereferences
mnt_ns->user_ns and panics.

Return false when the RCU read observes a detached mount. This keeps
the relaxed permission path conservative: a mount no longer attached
to a namespace cannot authorize open_by_handle_at() access.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-72034?


## How do I fix CVE-2026-72034?

Apply the vendor's patch.

## Is CVE-2026-72034 being exploited?

There is no known exploitation of CVE-2026-72034 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72034 and fix it if it is affected.

What it is: CVE-2026-72034 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-72034 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-2026-72034/ (Markdown: https://insights.sbomify.com/CVE-2026-72034/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72034
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72034
- OSV: https://osv.dev/vulnerability/CVE-2026-72034

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72034/
Summaries are generated and may contain mistakes; the official description above is the record.