---
id: CVE-2026-89656
title: 'libceph: reject buckets with mismatched CRUSH ids'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  libceph: reject buckets with mismatched CRUSH ids

  crush_decode() stores bucket data by array slot, and the mapper later
  derives the per-bucket workspace index from the…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-787
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 <
    ee59040d6ed1a5f8d10d27174b8f32c90ca8e89a
  - >-
    Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 <
    baad5875fdd2f5e248250fc3519bb045d64f1716
  - >-
    Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 <
    4aeb93daadf388e72073abc204312dd364eeb30a
  - >-
    Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 <
    6e5c6ce252b1eccfd41670a5cf95ab44f7ba7022
  - >-
    Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 <
    3516a4131c4e45d62ee4e42e82c36930e8c1fbbd
  - >-
    Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 <
    00562ccd4e88d092b9b851df50fad20442bfeb24
  - >-
    Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 <
    79900d978158b2d80eef952fc41b9e4dc58d7b83
  - >-
    Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 <
    3cde4a8302301679937474a5f7a851394cc1bd11
  - Linux 4.11
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-10-16T19:25:30.231032Z'
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:50:27.849Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89656'
references:
  - url: 'https://git.kernel.org/stable/c/ee59040d6ed1a5f8d10d27174b8f32c90ca8e89a'
  - url: 'https://git.kernel.org/stable/c/baad5875fdd2f5e248250fc3519bb045d64f1716'
  - url: 'https://git.kernel.org/stable/c/4aeb93daadf388e72073abc204312dd364eeb30a'
  - url: 'https://git.kernel.org/stable/c/6e5c6ce252b1eccfd41670a5cf95ab44f7ba7022'
  - url: 'https://git.kernel.org/stable/c/3516a4131c4e45d62ee4e42e82c36930e8c1fbbd'
  - url: 'https://git.kernel.org/stable/c/00562ccd4e88d092b9b851df50fad20442bfeb24'
  - url: 'https://git.kernel.org/stable/c/79900d978158b2d80eef952fc41b9e4dc58d7b83'
  - url: 'https://git.kernel.org/stable/c/3cde4a8302301679937474a5f7a851394cc1bd11'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89656.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89656'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532365'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89656'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89656'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89656.mbox
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
epss: 0.00514
epssPercentile: 0.43609
scores:
  cna: 9.8
  vendor: 8.8
ingestedAt: '2026-09-14T15:23:07.450Z'
---

## Overview

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

libceph: reject buckets with mismatched CRUSH ids

crush_decode() stores bucket data by array slot, and the mapper later
derives the per-bucket workspace index from the decoded bucket id. A
malformed map can therefore make one bucket reuse another bucket's
workspace by encoding an id different from -1 - slot.

For uniform buckets, the second replica selection expands the source
bucket's permutation into that aliased workspace buffer. If the source
bucket is larger than the aliased bucket, the write runs past the smaller
permutation array and can escape the kvmalloc'd CRUSH workspace. KASAN
reports a slab OOB write of 4 bytes in bucket_perm_choose().

Reject buckets whose encoded id does not match their array slot. Valid
CRUSH maps already use the canonical negative id corresponding to the
bucket slot, so this restores the invariant expected by
work->work[-1 - in->id] without changing valid map behavior.

## Affected

- `Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 < ee59040d6ed1a5f8d10d27174b8f32c90ca8e89a`
- `Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 < baad5875fdd2f5e248250fc3519bb045d64f1716`
- `Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 < 4aeb93daadf388e72073abc204312dd364eeb30a`
- `Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 < 6e5c6ce252b1eccfd41670a5cf95ab44f7ba7022`
- `Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 < 3516a4131c4e45d62ee4e42e82c36930e8c1fbbd`
- `Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 < 00562ccd4e88d092b9b851df50fad20442bfeb24`
- `Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 < 79900d978158b2d80eef952fc41b9e4dc58d7b83`
- `Linux >= 66a0e2d579dbec5c676cfe446234ffebb267c564 < 3cde4a8302301679937474a5f7a851394cc1bd11`
- `Linux 4.11`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · updated 2026-09-27 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89656.json)