CVE-2021-47640

Local KASAN bypass via stale shadow PTE

Published Feb 26, 2025 · Updated May 23, 2026

KASAN shadow-memory error in Linux 5.4 through 5.17.1 allows local users to evade detection of invalid vmalloc accesses. In arch/powerpc/mm/kasan/kasan_init_32.c, early shadow initialization leaves the page-table entry stale when PTE_RPN_SHIFT is 24 and PAGE_SHIFT is 12. The issue is limited to affected 32-bit PowerPC KASAN configurations; it produces false reports and suppresses detection of real vmalloc out-of-bounds accesses.

CVSS severity7.8
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

KASAN shadow-memory error in Linux 5.4 through 5.17.1 allows local users to evade detection of invalid vmalloc accesses. In arch/powerpc/mm/kasan/kasan_init_32.c, early shadow initialization leaves the page-table entry stale when PTE_RPN_SHIFT is 24 and PAGE_SHIFT is 12. The issue is limited to affected 32-bit PowerPC KASAN configurations; it produces false reports and suppresses detection of real vmalloc out-of-bounds accesses.

The record

CVE
CVE-2021-47640
Published
Feb 26, 2025
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-787
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 26, 2025CVE publishedPublication date reported by the CVE source.
  2. May 23, 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=3822dd8c102d11ada9d9ed8e04cad0b347a04689
  2. Affected versionversion=5.3.6 <5.4
  3. Affected versionversion=5.4
  4. Affected versionversion=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <5a3d8f3192a409893c57808cc935e16484df1068
  5. Affected versionversion=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <7f19245c3647afea8c7c41f795506ef70f64b9f2
  6. Affected versionversion=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <dd75080aa8409ce10d50fb58981c6b59bf8707d3
  7. Affected versionversion=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <de56beace6648065d404cd9835aa7d30e3df519d
  8. Affected versionversion=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <e3d157a4b4f4e0268c98be5b7013bf4b31234bb6
  9. Affected versionversion=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <f39a3309393a4a484532f6ba745c6acbcfe06115

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=3822dd8c102d11ada9d9ed8e04cad0b347a04689; version=5.3.6 <5.4; version=5.4; version=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <5a3d8f3192a409893c57808cc935e16484df1068; version=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <7f19245c3647afea8c7c41f795506ef70f64b9f2; version=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <dd75080aa8409ce10d50fb58981c6b59bf8707d3; version=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <de56beace6648065d404cd9835aa7d30e3df519d; version=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <e3d157a4b4f4e0268c98be5b7013bf4b31234bb6; version=cbd18991e24fea2c31da3bb117c83e4a3538cd11 <f39a3309393a4a484532f6ba745c6acbcfe06115

Published CVSS scores

7.8CISA ADP VulnrichmentCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write

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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