CVE-2021-47221

Memory corruption via misplaced freelist pointer

Published May 21, 2024 · Updated May 11, 2026

Memory corruption in Linux 5.7 through 5.12.12 allows local users to corrupt SLUB redzone data when redzoning is enabled. The SLUB allocator uses s->object_size instead of the larger in-use area when positioning a freelist pointer, so objects smaller than 24 bytes receive the pointer beyond the object boundary. Exploitation requires local access and SLUB redzoning; the kernel record states that no caches in the affected size range are known, limiting demonstrated impact to detected redzone corruption.

CVSS severity5.5
Medium
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in Linux 5.7 through 5.12.12 allows local users to corrupt SLUB redzone data when redzoning is enabled. The SLUB allocator uses s->object_size instead of the larger in-use area when positioning a freelist pointer, so objects smaller than 24 bytes receive the pointer beyond the object boundary. Exploitation requires local access and SLUB redzoning; the kernel record states that no caches in the affected size range are known, limiting demonstrated impact to detected redzone corruption.

The record

CVE
CVE-2021-47221
Published
May 21, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-763, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 21, 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=5.7
  2. Affected versionversion=89b83f282d8ba380cf2124f88106c57df49c538c <ce6e8bee7a3883e8008b30f5887dbb426aac6a35
  3. Affected versionversion=89b83f282d8ba380cf2124f88106c57df49c538c <e41a49fadbc80b60b48d3c095d9e2ee7ef7c9a8e
  4. Affected versionversion=89b83f282d8ba380cf2124f88106c57df49c538c <f6ed2357541612a13a5841b3af4dc32ed984a25f

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.7; version=89b83f282d8ba380cf2124f88106c57df49c538c <ce6e8bee7a3883e8008b30f5887dbb426aac6a35; version=89b83f282d8ba380cf2124f88106c57df49c538c <e41a49fadbc80b60b48d3c095d9e2ee7ef7c9a8e; version=89b83f282d8ba380cf2124f88106c57df49c538c <f6ed2357541612a13a5841b3af4dc32ed984a25f

Published CVSS scores

5.5NIST National Vulnerability DatabaseCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5SUSECVSS: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

CWE-763Release of Invalid Pointer or Reference
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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