# CVE-2026-89990: ceph: lock mutex in ceph_mds_check_access()

> A race condition in the Linux kernel Ceph client allows a use-after-free, potentially causing a system crash or arbitrary code execution.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-89990, DEBIAN-CVE-2026-89990, GHSA-pccj-hx6x-mqg3, UBUNTU-CVE-2026-89990

## What is CVE-2026-89990?

CVE-2026-89990 is a critical use after free vulnerability in Linux, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ceph: lock mutex in ceph_mds_check_access()

MDS session OPEN handling replaces mdsc->s_cap_auths under
mdsc->mutex, freeing the previous array and its strings.

ceph_mds_check_access() traverses this array without holding the
mutex.  A concurrent session reopen can therefore free the array while
it is being inspected, resulting in a use-after-free like this:

  Unable to handle kernel paging request at virtual address 003aaad64b2c8bb9
  [...]
  Internal error: Oops: 0000000096000004 [#1]  SMP
  Modules linked in:
  CPU: 56 UID: 2953037534 PID: 1253231 Comm: php-cgi8.4 Not tainted 6.18.45-i2-ampere #1146 NONE
  [..]
  pc : ceph_mds_check_access+0xd4/0x550
  lr : ceph_mds_check_access+0xc8/0x550
  [...]
  Call trace:
   ceph_mds_check_access+0xd4/0x550 (P)
   ceph_atomic_open+0x138/0xbe8
   path_openat+0xa24/0xfa8
   do_filp_open+0x94/0x158
   do_sys_openat2+0x88/0xf8

## Which versions are affected by CVE-2026-89990?


## How do I fix CVE-2026-89990?

Apply the vendor's patch.

## Is CVE-2026-89990 being exploited?

There is no known exploitation of CVE-2026-89990 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89990 and fix it if it is affected.

What it is: CVE-2026-89990 is a critical use after free vulnerability in Linux, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89990 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-2026-89990/ (Markdown: https://insights.sbomify.com/CVE-2026-89990/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89990
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89990
- OSV: https://osv.dev/vulnerability/CVE-2026-89990

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89990/
Summaries are generated and may contain mistakes; the official description above is the record.