# CVE-2026-89707: nfsd: release path refs on follow_down() error

> An authenticated NFS client can trigger a reference count leak in the Linux kernel, causing resource exhaustion and blocking unmount operations.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100529, BELL-CVE-2026-89707, DEBIAN-CVE-2026-89707, GHSA-qv85-292c-84hh, UBUNTU-CVE-2026-89707

## What is CVE-2026-89707?

CVE-2026-89707 is a high-severity denial of service vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

nfsd: release path refs on follow_down() error

nfsd_cross_mnt() initializes a local struct path with mntget() and
dget() before calling follow_down(). On a negative return the error
arm jumps to out without releasing those references:

    err = follow_down(&path, follow_flags);
    if (err < 0)
            goto out;

follow_down() never drops the caller's entry-time refs on any error
sub-case; for example a pre-cross d_manage() failure leaves path
untouched, so the mntget()/dget() taken on entry survive the call.

Every other early-exit arm in nfsd_cross_mnt() (other-namespace
return, IS_ERR(exp2), and the success tail after the swap) already
calls path_put(&path); the err < 0 arm is the lone omission. The
leak inflates mnt_count and d_count on each failed cross-mount,
blocking umount and pinning dentries against the shrinker, and is
reachable by any authenticated NFS client through nfsd_lookup_dentry
or the NFSv4 READDIR encode path.

Fix by calling path_put(&path) before the goto out in the err < 0
arm so the entry-time refs are released on all follow_down() error
returns.

## Which versions are affected by CVE-2026-89707?


## How do I fix CVE-2026-89707?

Apply the vendor's patch.

## Is CVE-2026-89707 being exploited?

There is no known exploitation of CVE-2026-89707 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89707 and fix it if it is affected.

What it is: CVE-2026-89707 is a high-severity denial of service vulnerability in Linux, published on 11 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89707 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-2026-89707/ (Markdown: https://insights.sbomify.com/CVE-2026-89707/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89707
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89707
- OSV: https://osv.dev/vulnerability/CVE-2026-89707

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89707/
Summaries are generated and may contain mistakes; the official description above is the record.