CVE-2021-47491

Local denial of service via special-file THP collapse

Published May 22, 2024 · Updated May 11, 2026

Denial of service in Linux khugepaged allows local users to crash the system via an executable mapping of a special file. The file-backed THP collapse path accepts any read-only VM_EXEC mapping without checking that the mapped inode is a regular file, so khugepaged can collapse pages belonging to block devices or other special files. Reachability requires local code to create the mapping while transparent huge pages and khugepaged are active; the documented consequence is kernel instability up to a system crash, with no confidentiality or integrity impact.

CVSS severity5.5
Medium
EPSS probability0.21%
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 Linux khugepaged allows local users to crash the system via an executable mapping of a special file. The file-backed THP collapse path accepts any read-only VM_EXEC mapping without checking that the mapped inode is a regular file, so khugepaged can collapse pages belonging to block devices or other special files. Reachability requires local code to create the mapping while transparent huge pages and khugepaged are active; the documented consequence is kernel instability up to a system crash, with no confidentiality or integrity impact.

The record

CVE
CVE-2021-47491
Published
May 22, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 22, 2024CVE 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

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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=5.4
  2. Affected versionversion=99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 <5fcb6fce74ffa614d964667110cf1a516c48c6d9
  3. Affected versionversion=99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 <6d67b2a73b8e3a079c355bab3c1aef7d85a044b8
  4. Affected versionversion=99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 <a4aeaa06d45e90f9b279f0b09de84bd00006e733

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.4; version=99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 <5fcb6fce74ffa614d964667110cf1a516c48c6d9; version=99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 <6d67b2a73b8e3a079c355bab3c1aef7d85a044b8; version=99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 <a4aeaa06d45e90f9b279f0b09de84bd00006e733

Published CVSS scores

5.5NVDCVSS: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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