CVE-2025-40287

Kernel hang via unchecked negative exFAT valid size

Published Dec 6, 2025 · Updated May 11, 2026

Denial of service in the Linux exFAT driver allows local users to hang the kernel through a malformed filesystem dentry. The exfat_find() size-validation path accepts a negative dentry.stream.valid_size value instead of returning an error. The flaw is reached when an affected kernel processes that entry and a local user invokes openat, ftruncate, or pwrite64.

CVSS severity5.5
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in the Linux exFAT driver allows local users to hang the kernel through a malformed filesystem dentry. The exfat_find() size-validation path accepts a negative dentry.stream.valid_size value instead of returning an error. The flaw is reached when an affected kernel processes that entry and a local user invokes openat, ftruncate, or pwrite64.

The record

CVE
CVE-2025-40287
Published
Dec 6, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 6, 2025CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=11a347fb6cef62ce47e84b97c45f2b2497c7593b <204b1b02ee018ba52ad2ece21fe3a8643d66a1b2
  2. Affected versionversion=11a347fb6cef62ce47e84b97c45f2b2497c7593b <6c627bcc1896ba62ec793d0c00da74f3c93ce3ad
  3. Affected versionversion=11a347fb6cef62ce47e84b97c45f2b2497c7593b <82ebecdc74ff555daf70b811d854b1f32a296bea
  4. Affected versionversion=6.8

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=11a347fb6cef62ce47e84b97c45f2b2497c7593b <204b1b02ee018ba52ad2ece21fe3a8643d66a1b2; version=11a347fb6cef62ce47e84b97c45f2b2497c7593b <6c627bcc1896ba62ec793d0c00da74f3c93ce3ad; version=11a347fb6cef62ce47e84b97c45f2b2497c7593b <82ebecdc74ff555daf70b811d854b1f32a296bea; version=6.8

Published CVSS scores

5.5SUSECVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5Amazon LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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