# CVE-2026-80561: libceph: fix multiple unsafe decodes in decode_locker()

> A malicious OSD can trigger slab-out-of-bounds reads in the Linux kernel Ceph client, potentially causing denial of service 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:** 26 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97784, BELL-CVE-2026-80561, DEBIAN-CVE-2026-80561, GHSA-g3cj-79m7-wg3j, UBUNTU-CVE-2026-80561

## What is CVE-2026-80561?

CVE-2026-80561 is a critical memory corruption vulnerability in Linux, published on 26 Aug 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: fix multiple unsafe decodes in decode_locker()

decode_locker() in cls_lock_client.c contains three unsafe decode
operations that allow a malicious or compromised OSD to trigger
slab-out-of-bounds reads:

1. ceph_decode_copy() at the locker_id_t name field has no preceding
   bounds check. With p == end after ceph_start_decoding() accepts
   struct_len=0, this reads sizeof(ceph_entity_name) = 9 bytes past
   the validated buffer boundary.

2. *p += sizeof(struct ceph_timespec) after the locker_info_t header
   is an unchecked pointer advance. A malicious OSD can position p
   past end, causing all subsequent _safe checks to pass against a
   bogus boundary.

3. len = ceph_decode_32(p) has no preceding bounds check, and the
   immediately following *p += len is uncapped. A malicious OSD can
   send len=0xffffffff, advancing p gigabytes past end and escaping
   the decode window entirely.

Fix all three by replacing bare operations with their safe variants:
  ceph_decode_copy   -> ceph_decode_copy_safe
  *p += sizeof(...)  -> ceph_decode_skip_n
  ceph_decode_32(p)  -> ceph_decode_32_safe
  *p += len          -> ceph_decode_skip_n

A new label is added to return -EINVAL on any bounds violation.
-EINVAL is appropriate here: the data received from the OSD
is structurally malformed, which is an invalid argument to the decode
contract regardless of whether the caller or the wire is at fault.

Attacker model: a malicious or compromised OSD in a multi-tenant Ceph
deployment can trigger this against any kernel client that issues the
lock.get_info class method (e.g. during RBD exclusive lock acquisition)
without any further privileges beyond OSD session establishment.

[ idryomov: use ceph_decode_skip_string() to skip description, trim
  changelog ]

## Which versions are affected by CVE-2026-80561?


## How do I fix CVE-2026-80561?

Apply the vendor's patch.

## Is CVE-2026-80561 being exploited?

There is no known exploitation of CVE-2026-80561 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80561 and fix it if it is affected.

What it is: CVE-2026-80561 is a critical memory corruption vulnerability in Linux, published on 26 Aug 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-2026-80561 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-2026-80561/ (Markdown: https://insights.sbomify.com/CVE-2026-80561/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80561
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80561
- OSV: https://osv.dev/vulnerability/CVE-2026-80561

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80561/
Summaries are generated and may contain mistakes; the official description above is the record.