# CVE-2026-89657: libceph: validate OSD extent maps before cursor advance

> A malicious Ceph OSD peer can crash the Linux kernel client by sending malformed sparse-read replies that trigger an assertion failure.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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-100554, BELL-CVE-2026-89657, DEBIAN-CVE-2026-89657, GHSA-9478-77xp-cr7g, UBUNTU-CVE-2026-89657

## What is CVE-2026-89657?

CVE-2026-89657 is a high-severity denial of service 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:

libceph: validate OSD extent maps before cursor advance

net/ceph/osd_client.c:osd_sparse_read() validates that the sparse-read
data length matches the summed extent lengths, but it does not validate
that each OSD-supplied extent is monotonic and lies inside the original
request range. A malformed authenticated OSD reply can advertise a
far-forward nonzero extent offset with a matching data length and make
the client advance the message-data cursor beyond the request buffer.
This reaches the BUG_ON(!*length) assertion in ceph_msg_data_next() from
the client receive path.

Impact: A malicious or compromised authenticated Ceph OSD peer can crash
a kernel Ceph client via a malformed sparse-read reply.

Reject sparse extent maps that overflow, move backwards, overlap, or
extend outside the original sparse-read request before advancing the
cursor.

[ idryomov: perform sparse_extent_map_valid() check a bit earlier,
  in CEPH_SPARSE_READ_DATA_LEN instead of CEPH_SPARSE_READ_DATA_PRE
  state ]

## Which versions are affected by CVE-2026-89657?


## How do I fix CVE-2026-89657?

Apply the vendor's patch.

## Is CVE-2026-89657 being exploited?

There is no known exploitation of CVE-2026-89657 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89657 and fix it if it is affected.

What it is: CVE-2026-89657 is a high-severity denial of service 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-2026-89657 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-2026-89657/ (Markdown: https://insights.sbomify.com/CVE-2026-89657/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89657
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89657
- OSV: https://osv.dev/vulnerability/CVE-2026-89657

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89657/
Summaries are generated and may contain mistakes; the official description above is the record.