CVE-2025-40040

Local memory-protection bypass via truncated VMA flags

Published Oct 28, 2025 · Updated Oct 28, 2025

A flag-handling flaw in the Linux kernel allows local users to crash the kernel or bypass memory protections through madvise(). In ksm_madvise(), complementing the 32-bit VM_MERGEABLE constant before promotion to unsigned long zeroes the upper 32 bits of vm_flags rather than clearing only the mergeable bit. An unprivileged process can trigger the deterministic path in its own address space; affected flags can cause a panic on userfaultfd close or remove sealing, protection-key, and shadow-stack controls.

CVSS severity7.8
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A flag-handling flaw in the Linux kernel allows local users to crash the kernel or bypass memory protections through madvise(). In ksm_madvise(), complementing the 32-bit VM_MERGEABLE constant before promotion to unsigned long zeroes the upper 32 bits of vm_flags rather than clearing only the mergeable bit. An unprivileged process can trigger the deterministic path in its own address space; affected flags can cause a panic on userfaultfd close or remove sealing, protection-key, and shadow-stack controls.

The record

CVE
CVE-2025-40040
Published
Oct 28, 2025
Updated
Oct 28, 2025
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 28, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 28, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=5.13
  2. Affected versionversion=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5 <76385629f45740b7888f8fcd83bde955b10f61fe
  3. Affected versionversion=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5 <92b82e232b8d8b116ac6e57aeae7a6033db92c60
  4. Affected versionversion=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5 <ac50c6e0a8f91a02b681af81abb2362fbb67cc18
  5. Affected versionversion=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5 <f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.13; version=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5 <76385629f45740b7888f8fcd83bde955b10f61fe; version=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5 <92b82e232b8d8b116ac6e57aeae7a6033db92c60; version=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5 <ac50c6e0a8f91a02b681af81abb2362fbb67cc18; version=7677f7fd8be76659cd2d0db8ff4093bbb51c20e5 <f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93

Published CVSS scores

7.8LinuxCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
5.8OracleCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/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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