CVE-2021-47221

MEDIUMNVD 5.55.5—
EchelonGraph scoreMEDIUM confidence

Score 5.5 from GitHub Security Advisory published 2024-05-21. NVD baseline CVSS 5.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
5.5
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 5.5Exploit: NoneExposed: 0

A fix is available — apply it.

In the Linux kernel, the following vulnerability has been resolved:

mm/slub: actually fix freelist pointer vs redzoning

It turns out that SLUB redzoning ("slub_debug=Z") checks from s->object_size rather than from s->inuse (which is normally bumped to make room for the freelist pointer), so a cache created with an object size less than 24 would have the freelist pointer written beyond s->object_size, causing the redzone to be corrupted by the freelist pointer. This was very visible with "slub_debug=ZF":

BUG test (Tainted: G B ): Right Redzone overwritten -----------------------------------------------------------------------------

INFO: 0xffff957ead1c05de-0xffff957ead1c05df @offset=1502. First byte 0x1a instead of 0xbb INFO: Slab 0xffffef3950b47000 objects=170 used=170 fp=0x0000000000000000 flags=0x8000000000000200 INFO: Object 0xffff957ead1c05d8 @offset=1496 fp=0xffff957ead1c0620

Redzone (____ptrval____): bb bb bb bb bb bb bb bb ........ Object (____ptrval____): 00 00 00 00 00 f6 f4 a5 ........ Redzone (____ptrval____): 40 1d e8 1a aa @.... Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........

Adjust the offset to stay within s->object_size.

(Note that no caches of in this size range are known to exist in the kernel currently.)

CVSS v3
5.5
EG Score
5.5(medium)
EPSS
12.9%
KEV
Not listed

Published

May 21, 2024

Last Modified

April 29, 2025

References (6)

Vendor Advisories for CVE-2021-47221(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatkernel-0:4.18.0-477.10.1.el8_82023-05-16redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 9× in last 7d / 45× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-22 14:06 UTCEPSS rescore
  2. 2026-07-21 15:22 UTCEPSS rescore
  3. 2026-07-21 15:22 UTCEPSS rescore
  4. 2026-07-20 17:05 UTCEPSS rescore
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  13. 2026-07-14 09:55 UTCOSV refresh
  14. 2026-07-13 06:11 UTCEPSS rescore
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  1. 2026-07-05 02:28 UTCEPSS rescore
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  5. 2026-07-01 15:04 UTCEPSS rescore
  6. 2026-06-30 23:20 UTCEPSS rescore
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  12. 2026-06-27 03:07 UTCEPSS rescore
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  14. 2026-06-26 10:39 UTCOSV refresh
  15. 2026-06-25 13:48 UTCEPSS rescore
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  17. 2026-06-24 14:03 UTCEPSS rescore
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  19. 2026-06-23 21:31 UTCEPSS rescore
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  21. 2026-06-22 14:24 UTCEPSS rescore
  22. 2026-06-21 14:55 UTCEPSS rescore
  23. 2026-06-21 01:58 UTCEPSS rescore
  24. 2026-06-21 01:58 UTCEPSS rescore
  25. 2026-06-19 19:24 UTCEPSS rescore
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  27. 2026-06-18 17:51 UTCEPSS rescore
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  39. 2026-06-10 22:16 UTCEPSS rescore
  40. 2026-06-10 13:20 UTCEPSS rescore
  41. 2026-06-08 17:11 UTCOSV refresh
  42. 2026-06-08 14:15 UTCEPSS rescore
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  44. 2026-06-08 14:15 UTCEPSS rescore
  45. 2026-06-07 15:23 UTCEPSS rescore
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  47. 2026-06-06 13:46 UTCEPSS rescore
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  49. 2026-06-05 22:45 UTCEPSS rescore
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  59. 2026-05-31 22:29 UTCEPSS rescore
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  62. 2026-05-29 13:42 UTCEPSS rescore
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  65. 2026-05-27 13:39 UTCEPSS rescore
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  70. 2026-05-26 07:17 UTCEPSS rescore
  71. 2026-05-24 01:39 UTCEG score recompute
  72. 2026-05-24 01:39 UTCVendor advisory
  73. 2026-05-24 01:39 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2021-47221?
CVE-2021-47221 is a medium vulnerability published on May 21, 2024. In the Linux kernel, the following vulnerability has been resolved: mm/slub: actually fix freelist pointer vs redzoning It turns out that SLUB redzoning ("slub_debug=Z") checks from s->object_size rather than from s->inuse (which is normally bumped to make room for the freelist pointer), so a cache…
When was CVE-2021-47221 disclosed?
CVE-2021-47221 was first published in the National Vulnerability Database on May 21, 2024, with the most recent update on April 29, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-47221 actively exploited?
CVE-2021-47221 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 12.9% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-47221?
CVE-2021-47221 has a CVSS v3 base score of 5.5 (NVD).
How do I remediate CVE-2021-47221?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-47221, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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