---
id: CVE-2026-64298
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  NFSv4: include MAY_WRITE in open permission mask for O_TRUNC

  POSIX requires write permission to truncate a file, so an open() that
  specifies O_TRUNC must be authorized…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  NFSv4: include MAY_WRITE in open permission mask for O_TRUNC

  POSIX requires write permission to truncate a file, so an open() that
  specifies O_TRUNC must be authorized…
severity: high
cvss: 7.1
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H'
published: '2026-07-25'
updated: '2026-07-27'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64298'
references:
  - url: 'https://git.kernel.org/stable/c/22c1fd1355ad4ca27aa7f0fa02719122dd92d9de'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/30fdf4df6c3c00efec947e4ddf97f0fdd4473628'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4817c8974315b666e895b7d1bb83cd3664c323b1'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/5140f099ecd8a2f2808b7f7b720ee1bad8468974'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6bd7d0a06b53c4e797e1a9cea0d2d41aa1b26230'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a937e92c1d00534b5c2e3e9f4381b7e988180797'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cb148a2762d644bff1894728e8835a9a4b84f9ea'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/e36501b7d4abdcd6d69a7cb901b2f286b7a3d041'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00164
epssPercentile: 0.04959
ingestedAt: '2026-07-27T06:16:50.194Z'
---

## Overview

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

NFSv4: include MAY_WRITE in open permission mask for O_TRUNC

POSIX requires write permission to truncate a file, so an open() that
specifies O_TRUNC must be authorized for write access regardless of the
O_ACCMODE access mode.

nfs_open_permission_mask() builds the access mask passed to
nfs_may_open(), which is the local authorization gate for OPENs the
client serves itself from a cached write delegation via the
can_open_delegated() path in nfs4_try_open_cached().  The mask is
derived from O_ACCMODE alone, so an open(O_RDONLY | O_TRUNC) against a
file the caller cannot write requests only MAY_READ and passes the
local check.  The OPEN is then satisfied locally and the truncation is
issued to the server as a SETATTR(size=0) over the delegation stateid,
which the server accepts under standard write-delegation semantics.
POSIX requires that this open fail with EACCES.

Include MAY_WRITE in the mask whenever O_TRUNC is set so the local
check matches the access the server would have enforced.

## Remediation

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