# CVE-2026-90266: btrfs: zoned: don't force read-only on transient -EAGAIN from reloc merge

> A local attacker can cause a denial of service on zoned Btrfs filesystems by triggering transient errors during reclaim, aborting transactions.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-90266, GHSA-gj86-9624-3gxh, UBUNTU-CVE-2026-90266

## What is CVE-2026-90266?

CVE-2026-90266 is a denial of service vulnerability in Linux, published on 17 Sep 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:

btrfs: zoned: don't force read-only on transient -EAGAIN from reloc merge

On a zoned FS, btrfs_delayed_refs_rsv_refill() returns -EAGAIN whenever
the over-committed metadata plus the zone_unusable bytes exceeds the
usable size in a metadata block-group to avoid heavy over-commit of
metadata and early ENOSPC in one transaction.

If this happens while doing reclaim, the transaction is getting aborted.

Treat -EAGAIN as a soft, retryable condition in case of block-group
reclaim.

## Which versions are affected by CVE-2026-90266?


## How do I fix CVE-2026-90266?

Apply the vendor's patch.

## Is CVE-2026-90266 being exploited?

There is no known exploitation of CVE-2026-90266 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90266 and fix it if it is affected.

What it is: CVE-2026-90266 is a denial of service vulnerability in Linux, published on 17 Sep 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-2026-90266 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-2026-90266/ (Markdown: https://insights.sbomify.com/CVE-2026-90266/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90266
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90266
- OSV: https://osv.dev/vulnerability/CVE-2026-90266

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90266/
Summaries are generated and may contain mistakes; the official description above is the record.