---
id: CVE-2025-40287
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  exfat: fix improper check of dentry.stream.valid_size

  We found an infinite loop bug in the exFAT file system that can lead to a
  Denial-of-Service (DoS) condition
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  exfat: fix improper check of dentry.stream.valid_size

  We found an infinite loop bug in the exFAT file system that can lead to a
  Denial-of-Service (DoS) condition. When…
severity: none
published: '2025-12-06'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T19:10:00.173'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-40287'
references:
  - url: 'https://git.kernel.org/stable/c/204b1b02ee018ba52ad2ece21fe3a8643d66a1b2'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6c627bcc1896ba62ec793d0c00da74f3c93ce3ad'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/82ebecdc74ff555daf70b811d854b1f32a296bea'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00185
epssPercentile: 0.07569
ingestedAt: '2026-10-15T19:25:46.336Z'
---

## Overview

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

exfat: fix improper check of dentry.stream.valid_size

We found an infinite loop bug in the exFAT file system that can lead to a
Denial-of-Service (DoS) condition. When a dentry in an exFAT filesystem is
malformed, the following system calls — SYS_openat, SYS_ftruncate, and
SYS_pwrite64 — can cause the kernel to hang.

Root cause analysis shows that the size validation code in exfat_find()
does not check whether dentry.stream.valid_size is negative. As a result,
the system calls mentioned above can succeed and eventually trigger the DoS
issue.

This patch adds a check for negative dentry.stream.valid_size to prevent
this vulnerability.

## Remediation

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