# CVE-2026-53393: nfsd: reset write verifier on deferred writeback errors


- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** AZL-92600, BELL-CVE-2026-53393, DEBIAN-CVE-2026-53393, GHSA-wm3m-j54f-523v, ROOT-OS-DEBIAN-11-CVE-2026-53393, ROOT-OS-DEBIAN-12-CVE-2026-53393, ROOT-OS-UBUNTU-2204-CVE-2026-53393, UBUNTU-CVE-2026-53393

## What is CVE-2026-53393?

CVE-2026-53393 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 2026. 

### Official description

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

nfsd: reset write verifier on deferred writeback errors

nfsd_vfs_write() and nfsd_commit() both call filemap_check_wb_err() to
detect deferred writeback errors, but neither rotates the server's write
verifier (nn->writeverf) when this check fails. Every other
durable-storage-failure path in these functions calls
commit_reset_write_verifier() before returning an error.

The missing rotation means clients holding UNSTABLE write data under the
current verifier will COMMIT, receive the unchanged verifier back, and
conclude their data is durable — silently dropping data that failed
writeback. This violates the UNSTABLE+COMMIT durability contract
(RFC 1813 §3.3.7, RFC 8881 §18.32).

Add commit_reset_write_verifier() calls at both filemap_check_wb_err()
error sites, matching the pattern used by adjacent error paths in the
same functions. The helper already filters -EAGAIN and -ESTALE
internally, so the calls are unconditionally safe.

## Which versions are affected by CVE-2026-53393?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53393?

Upgrade to a fixed version.

## Is CVE-2026-53393 being exploited?

There is no known exploitation of CVE-2026-53393 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-53393 and fix it if it is affected.

What it is: CVE-2026-53393 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 2026. 
Exploitation: There is no known exploitation of CVE-2026-53393 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-53393/ (Markdown: https://insights.sbomify.com/CVE-2026-53393/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53393
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53393
- OSV: https://osv.dev/vulnerability/CVE-2026-53393

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53393/
Summaries are generated and may contain mistakes; the official description above is the record.