# CVE-2026-90260: btrfs: zoned: don't clobber the extent buffer when zeroing it out

> A use-after-free style memory corruption in the Linux kernel's btrfs zoned filesystem can cause extent tree corruption and system crashes.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/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:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** BELL-CVE-2026-90260, DEBIAN-CVE-2026-90260, GHSA-3xv6-4m2c-phmw, UBUNTU-CVE-2026-90260

## What is CVE-2026-90260?

CVE-2026-90260 is a high-severity memory corruption 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 clobber the extent buffer when zeroing it out

On a zoned filesystem a freed-but-still-dirty tree block is written out
as zeros (EXTENT_BUFFER_ZONED_ZEROOUT) only to keep the zone write
pointer advancing. btree_csum_one_bio() implemented this by memzeroing
the extent buffer's own folios before submission.

That destroys the in-memory buffer while it may still be referenced. In
particular btrfs_free_tree_block() can run on it afterwards and reads
the header to add a delayed reference; once the header has been zeroed
it frees bytenr 0 and corrupts the extent tree (the
btrfs_header_bytenr(buf) != 0 ASSERT in btrfs_free_tree_block(), or an
"unable to find ref" abort). It is flaky and reproduces under fsstress,
e.g. generic/461 and generic/013.

Write the zeros to disk from the shared zero page instead and leave the
extent buffer content untouched, so any later reference - including the
delayed reference from btrfs_free_tree_block() - still sees a valid
header. end_bbio_meta_write() now clears writeback on the buffer's own
folios, as the bio no longer carries them.

## Which versions are affected by CVE-2026-90260?


## How do I fix CVE-2026-90260?

Apply the vendor's patch.

## Is CVE-2026-90260 being exploited?

There is no known exploitation of CVE-2026-90260 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90260 and fix it if it is affected.

What it is: CVE-2026-90260 is a high-severity memory corruption 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-2026-90260 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-2026-90260/ (Markdown: https://insights.sbomify.com/CVE-2026-90260/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90260
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90260
- OSV: https://osv.dev/vulnerability/CVE-2026-90260

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90260/
Summaries are generated and may contain mistakes; the official description above is the record.