---
id: CVE-2026-89793
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ublk: clear VM_MAYWRITE on read-only ublk char device mmap

  ublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never
  clears VM_MAYWRITE on the resulting read-o…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ublk: clear VM_MAYWRITE on read-only ublk char device mmap

  ublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never
  clears VM_MAYWRITE on the resulting read-o…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    be41733c24be58e2a1ef718c80fafdfb98a40d5e
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    5befd06a72216869b607cf7724a4f16c6a2d3999
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    e373c1acdbcf88cec533ece9f589020adaed0a78
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    fa5e1bc673ca59722608af67b27e65dba0c97926
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    6e2b571b0a54755b06e092501913e1dfefe75d6c
  - Linux < 6.6.157
  - Linux < 6.12.110
  - Linux < 6.18.51
  - Linux < 7.2.5
  - Linux (all versions)
published: '2026-09-16'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T15:18:09.510'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89793'
references:
  - url: 'https://git.kernel.org/stable/c/5befd06a72216869b607cf7724a4f16c6a2d3999'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6e2b571b0a54755b06e092501913e1dfefe75d6c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/be41733c24be58e2a1ef718c80fafdfb98a40d5e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/e373c1acdbcf88cec533ece9f589020adaed0a78'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/fa5e1bc673ca59722608af67b27e65dba0c97926'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-16T10:53:53.925Z'
epss: 0.00175
epssPercentile: 0.06147
---

## Overview

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

ublk: clear VM_MAYWRITE on read-only ublk char device mmap

ublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never
clears VM_MAYWRITE on the resulting read-only mapping. This allows
a userspace daemon to mmap the per-queue command buffer PROT_READ,
then upgrade it to PROT_WRITE via mprotect(), since VM_MAYWRITE was
never cleared.

The command buffer holds struct ublksrv_io_desc entries that are
kernel-written ABI; a writable mapping lets an unprivileged daemon
process corrupt fields such as addr, op_flags, nr_sectors, and
start_sector.

Same bug class as the drm/panthor and drm/vc4 VM_MAYWRITE fixes, and
the 2026-08-13 ptp/vmclock fix (a5edadbae57e).

Verified via mprotect() PoC: before the fix, a PROT_READ mapping can
be upgraded to PROT_READ|PROT_WRITE and a write into the command
buffer corrupts io_desc fields (confirmed under KASAN). After the
fix, mprotect() returns -EACCES.

## Remediation

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