---
id: CVE-2026-89651
title: 'ceph: bound MDSCapAuth path and fs_name decode in handle_session()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ceph: bound MDSCapAuth path and fs_name decode in handle_session()

  handle_session() decodes the MDSCapAuth records carried by a
  CEPH_SESSION_OPEN message (msg_version …
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-125
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1d17de9534cb5a4c4c380d174cc2f9281b34f89e <
    dc5c7dffda92ef372fa587c444a1c537373df824
  - >-
    Linux >= 1d17de9534cb5a4c4c380d174cc2f9281b34f89e <
    c37db86d2b5e9b57001ccae7e7a727e95a4f9c02
  - >-
    Linux >= 1d17de9534cb5a4c4c380d174cc2f9281b34f89e <
    5f892c767b30e4fb0c744c59f9235c717383d2cd
  - >-
    Linux >= 1d17de9534cb5a4c4c380d174cc2f9281b34f89e <
    77933e22adfe813be2bd10be08d6e950103c3967
  - Linux 6.10
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:50:22.893Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89651'
references:
  - url: 'https://git.kernel.org/stable/c/dc5c7dffda92ef372fa587c444a1c537373df824'
  - url: 'https://git.kernel.org/stable/c/c37db86d2b5e9b57001ccae7e7a727e95a4f9c02'
  - url: 'https://git.kernel.org/stable/c/5f892c767b30e4fb0c744c59f9235c717383d2cd'
  - url: 'https://git.kernel.org/stable/c/77933e22adfe813be2bd10be08d6e950103c3967'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89651.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89651'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532282'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89651'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89651'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89651.mbox
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.00635
epssPercentile: 0.50213
scores:
  cna: 9.8
  vendor: 7
ingestedAt: '2026-09-14T15:23:07.473Z'
---

## Overview

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

ceph: bound MDSCapAuth path and fs_name decode in handle_session()

handle_session() decodes the MDSCapAuth records carried by a
CEPH_SESSION_OPEN message (msg_version >= 6). For each record the
match.path and match.fs_name byte strings are read by first decoding a
32-bit length and then copying that many bytes with the bare
ceph_decode_copy(). Unlike the surrounding fields, which all use the
_safe decode variants, these two copies are not preceded by a
ceph_decode_need() bounds check, and the enclosing MDSCapAuth and
MDSCapMatch struct_len fields are skipped rather than enforced as an
upper bound. A length larger than the bytes remaining in the message
front makes ceph_decode_copy() read past the end of the front buffer.

The message front is a dedicated allocation (ceph_msg_new2() ->
kvmalloc), so the over-read runs off that object. A malicious or
compromised MDS can trigger this with the first post-connect message on
mount, with no client-side user interaction; under KASAN it is reported
as a slab-out-of-bounds read in handle_session().

Impact: a malicious MDS can force the kernel client to read up to 4 GiB
past the message front allocation during session setup, crashing the
client (out-of-bounds read).

Switch both copies to ceph_decode_copy_safe(), which performs the
ceph_decode_need() bounds check before the copy and branches to the
existing bad label, matching the rest of the decoder and the error path
that frees the partially decoded cap_auths array.

## Affected

- `Linux >= 1d17de9534cb5a4c4c380d174cc2f9281b34f89e < dc5c7dffda92ef372fa587c444a1c537373df824`
- `Linux >= 1d17de9534cb5a4c4c380d174cc2f9281b34f89e < c37db86d2b5e9b57001ccae7e7a727e95a4f9c02`
- `Linux >= 1d17de9534cb5a4c4c380d174cc2f9281b34f89e < 5f892c767b30e4fb0c744c59f9235c717383d2cd`
- `Linux >= 1d17de9534cb5a4c4c380d174cc2f9281b34f89e < 77933e22adfe813be2bd10be08d6e950103c3967`
- `Linux 6.10`

## Remediation

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

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9 · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89651.json)