# CVE-2026-31666: btrfs: fix incorrect return value after changing leaf in lookup_extent_data_ref()

> Incorrect return value in btrfs lookup can cause extent tree corruption by allowing operations on wrong items.

- **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:** 24 Apr 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-31666, DEBIAN-CVE-2026-31666, GHSA-7wrc-m37g-996x, ROOT-OS-DEBIAN-13-CVE-2026-31666, UBUNTU-CVE-2026-31666

## What is CVE-2026-31666?

CVE-2026-31666 is a high-severity vulnerability in Linux kernel, published on 24 Apr 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: fix incorrect return value after changing leaf in lookup_extent_data_ref()

After commit 1618aa3c2e01 ("btrfs: simplify return variables in
lookup_extent_data_ref()"), the err and ret variables were merged into
a single ret variable. However, when btrfs_next_leaf() returns 0
(success), ret is overwritten from -ENOENT to 0. If the first key in
the next leaf does not match (different objectid or type), the function
returns 0 instead of -ENOENT, making the caller believe the lookup
succeeded when it did not. This can lead to operations on the wrong
extent tree item, potentially causing extent tree corruption.

Fix this by returning -ENOENT directly when the key does not match,
instead of relying on the ret variable.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2026-31666?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31666?

Apply the vendor's patch.

## Is CVE-2026-31666 being exploited?

There is no known exploitation of CVE-2026-31666 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-2026-31666 and fix it if it is affected.

What it is: CVE-2026-31666 is a high-severity vulnerability in Linux kernel, published on 24 Apr 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-2026-31666 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-2026-31666/ (Markdown: https://insights.sbomify.com/CVE-2026-31666/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31666
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31666
- OSV: https://osv.dev/vulnerability/CVE-2026-31666

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31666/
Summaries are generated and may contain mistakes; the official description above is the record.