# CVE-2026-89653: ceph: reject export_targets ranks >= CEPH_MAX_MDS in mdsmap decode

> A buffer overflow in the Linux kernel Ceph MDS map decoder allows attackers to write past array bounds, potentially causing crashes or 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:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100418, BELL-CVE-2026-89653, DEBIAN-CVE-2026-89653, GHSA-q4wh-f6ch-5m9w, UBUNTU-CVE-2026-89653

## What is CVE-2026-89653?

CVE-2026-89653 is a critical memory corruption vulnerability in Linux, published on 11 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: reject export_targets ranks >= CEPH_MAX_MDS in mdsmap decode

MDSMap export_targets entries are monitor controlled. check_new_map()
uses each entry as a bit number in a fixed stack bitmap, so a rank
outside the protocol namespace can make set_bit() write past the end of
the array.

Reject ranks outside CEPH_MAX_MDS while decoding the map. Do not
validate against possible_max_rank here because maps may legitimately
reference ranks beyond a temporarily reduced max_mds.

## Which versions are affected by CVE-2026-89653?


## How do I fix CVE-2026-89653?

Apply the vendor's patch.

## Is CVE-2026-89653 being exploited?

There is no known exploitation of CVE-2026-89653 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89653 and fix it if it is affected.

What it is: CVE-2026-89653 is a critical memory corruption vulnerability in Linux, published on 11 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-2026-89653 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-2026-89653/ (Markdown: https://insights.sbomify.com/CVE-2026-89653/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89653
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89653
- OSV: https://osv.dev/vulnerability/CVE-2026-89653

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89653/
Summaries are generated and may contain mistakes; the official description above is the record.