---
id: CVE-2026-31611
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ksmbd: require 3 sub-authorities before reading sub_auth[2]

  parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on
  match reads sid.sub_auth[2] as the file…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ksmbd: require 3 sub-authorities before reading sub_auth[2]

  parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on
  match reads sid.sub_auth[2] as the file…
severity: high
cvss: 8.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H'
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.15, < 6.6.136'
  - 'linux_kernel >= 6.7, < 6.12.83'
  - 'linux_kernel >= 6.13, < 6.18.24'
  - 'linux_kernel >= 6.19, < 6.19.14'
  - 'linux_kernel >= 7.0, < 7.0.1'
patched:
  - linux_kernel 7.0.1
published: '2026-04-24'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:19:12.263'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31611'
references:
  - url: 'https://git.kernel.org/stable/c/08f9e6d899b5c834bbcc239eae1bed58d9b15d2c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/46bbcd3ebfb3549c8da1838fc4493e79bd3241e7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/53370cf9090777774e07fd9a8ebce67c6cc333ab'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9401f86a224f37b50e6a3ccf1d46a70d5ef8af0a'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b5b5d5936a50497fb151c0b122899a6894721c2b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cf2148b880fb7c0fcd727202dbc4fd5d6998b9c2'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d2454f4a002d08560a60f214f392e6491cf11560'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-784472.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00524
epssPercentile: 0.4304
ingestedAt: '2026-10-15T03:30:12.859Z'
---

## Overview

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

ksmbd: require 3 sub-authorities before reading sub_auth[2]

parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on
match reads sid.sub_auth[2] as the file mode.  If sid_unix_NFS_mode is
the prefix S-1-5-88-3 with num_subauth = 2 then compare_sids() compares
only min(num_subauth, 2) sub-authorities so a client SID with
num_subauth = 2 and sub_auth = {88, 3} will match.

If num_subauth = 2 and the ACE is placed at the very end of the security
descriptor, sub_auth[2] will be  4 bytes past end_of_acl.  The
out-of-band bytes will then be masked to the low 9 bits and applied as
the file's POSIX mode, probably not something that is good to have
happen.

Fix this up by forcing the SID to actually carry a third sub-authority
before reading it at all.

## Affected

- `linux_kernel >= 5.15, < 6.6.136`
- `linux_kernel >= 6.7, < 6.12.83`
- `linux_kernel >= 6.13, < 6.18.24`
- `linux_kernel >= 6.19, < 6.19.14`
- `linux_kernel >= 7.0, < 7.0.1`

## Remediation

Upgrade past the affected range:

- `linux_kernel 7.0.1`