# CVE-2026-99040: KEYS: Fix add_key() race with keyring restriction


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** AZL-110915, BELL-CVE-2026-99040, DEBIAN-CVE-2026-99040, GHSA-xfxp-jqfr-m4g5, UBUNTU-CVE-2026-99040

## What is CVE-2026-99040?

CVE-2026-99040 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

KEYS: Fix add_key() race with keyring restriction

__key_create_or_update() snapshots keyring->restrict_link before taking
the destination keyring's semaphore.  keyring_restrict() installs a
restriction while holding that semaphore.

This allows a writer to observe no restriction, wait for the keyring
owner to install a reject-all restriction and return successfully, and
then link a key using the stale NULL snapshot.  The writer only needs
write permission on the destination keyring.

Move the restrict_link read after __key_link_lock() and
__key_link_begin().  The read and the subsequent restriction check are
then serialized with restriction installation by keyring->sem.

The race was reproduced on v7.2.8 in 19 executions where restriction
installation returned before the link completed.  All 19 linked the key
despite the reject-all restriction.  With this change, 312 executions
reached the same ordering and every add_key() call failed with -EPERM.

The issue was found by manual concurrency analysis assisted by AI-based
analysis and independently verified with a QEMU reproducer and kernel
instrumentation.

## Which versions are affected by CVE-2026-99040?


## How do I fix CVE-2026-99040?

Upgrade to a fixed version.

## Is CVE-2026-99040 being exploited?

There is no known exploitation of CVE-2026-99040 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99040 and fix it if it is affected.

What it is: CVE-2026-99040 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99040 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-2026-99040/ (Markdown: https://insights.sbomify.com/CVE-2026-99040/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99040
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99040
- OSV: https://osv.dev/vulnerability/CVE-2026-99040

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99040/
Summaries are generated and may contain mistakes; the official description above is the record.