CVE-2021-47566

HIGHNVD 7.87.8
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

This high-severity CVE scores 7.8 under NVD CVSS v3. EPSS exploit probability: 0.2% (12th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, NVD CVSS v3
Trending — 3 sources updated this week
7.8EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 7.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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

proc/vmcore: fix clearing user buffer by properly using clear_user()

To clear a user buffer we cannot simply use memset, we have to use clear_user(). With a virtio-mem device that registers a vmcore_cb and has some logically unplugged memory inside an added Linux memory block, I can easily trigger a BUG by copying the vmcore via "cp":

systemd[1]: Starting Kdump Vmcore Save Service... kdump[420]: Kdump is using the default log level(3). kdump[453]: saving to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ kdump[458]: saving vmcore-dmesg.txt to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ kdump[465]: saving vmcore-dmesg.txt complete kdump[467]: saving vmcore BUG: unable to handle page fault for address: 00007f2374e01000 #PF: supervisor write access in kernel mode #PF: error_code(0x0003) - permissions violation PGD 7a523067 P4D 7a523067 PUD 7a528067 PMD 7a525067 PTE 800000007048f867 Oops: 0003 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 468 Comm: cp Not tainted 5.15.0+ #6 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-27-g64f37cc530f1-prebuilt.qemu.org 04/01/2014 RIP: 0010:read_from_oldmem.part.0.cold+0x1d/0x86 Code: ff ff ff e8 05 ff fe ff e9 b9 e9 7f ff 48 89 de 48 c7 c7 38 3b 60 82 e8 f1 fe fe ff 83 fd 08 72 3c 49 8d 7d 08 4c 89 e9 89 e8 <49> c7 45 00 00 00 00 00 49 c7 44 05 f8 00 00 00 00 48 83 e7 f81 RSP: 0018:ffffc9000073be08 EFLAGS: 00010212 RAX: 0000000000001000 RBX: 00000000002fd000 RCX: 00007f2374e01000 RDX: 0000000000000001 RSI: 00000000ffffdfff RDI: 00007f2374e01008 RBP: 0000000000001000 R08: 0000000000000000 R09: ffffc9000073bc50 R10: ffffc9000073bc48 R11: ffffffff829461a8 R12: 000000000000f000 R13: 00007f2374e01000 R14: 0000000000000000 R15: ffff88807bd421e8 FS: 00007f2374e12140(0000) GS:ffff88807f000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f2374e01000 CR3: 000000007a4aa000 CR4: 0000000000350eb0 Call Trace: read_vmcore+0x236/0x2c0 proc_reg_read+0x55/0xa0 vfs_read+0x95/0x190 ksys_read+0x4f/0xc0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae

Some x86-64 CPUs have a CPU feature called "Supervisor Mode Access Prevention (SMAP)", which is used to detect wrong access from the kernel to user buffers like this: SMAP triggers a permissions violation on wrong access. In the x86-64 variant of clear_user(), SMAP is properly handled via clac()+stac().

To fix, properly use clear_user() when we're dealing with a user buffer.

CVSS v3
7.8
EG Score
7.8HIGHmedium confidence
EG Risk
35
EG Risk 35/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity78% × 45%
Impact severity (EG Severity): CVSS 7.8 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.2% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.2%
EPSS %ILE
12th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (7.8): severity, escalated by confirmed exploitation. This CVE's 7.8 is its impact severity (EG Severity), not escalated.

EG Severity
7.8 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-20). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

May 24, 2024

Last Modified

September 18, 2025

Advisory Details (8)

Auto-updated Oct 11, 2026
Patch available.
Web page

proc/vmcore: fix clearing user buffer by properly using clear_user() - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/7b3a34f08d11e7f05cd00b8e09adaa15192f0ad1
Web page

proc/vmcore: fix clearing user buffer by properly using clear_user() - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/33a7d698f30fa0b99d50569e9909d3baa65d8f6a
Web page

proc/vmcore: fix clearing user buffer by properly using clear_user() - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/fd7974c547abfb03072a4ee706d3a6f182266f89
Web page

proc/vmcore: fix clearing user buffer by properly using clear_user() - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/c1e63117711977cc4295b2ce73de29dd17066c82
Web page

proc/vmcore: fix clearing user buffer by properly using clear_user() - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/a9e164bd160be8cbee1df70acb379129e3cd2e7c
Web page

proc/vmcore: fix clearing user buffer by properly using clear_user() - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/a8a917058faf4abaec9fb614bb6d5f8fe3529ec6
Web page

proc/vmcore: fix clearing user buffer by properly using clear_user() - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/9ef384ed300d1bcfb23d0ab0b487d544444d4b52
Web page

proc/vmcore: fix clearing user buffer by properly using clear_user() - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/99d348b82bcb36171f24411d3f1a15706a2a937a

Vendor Advisories for CVE-2021-47566(2)

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

Patch Availability(2)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatkernel-0:4.18.0-477.74.1.el8_82024-09-24redhat
redhatkernel-0:4.18.0-372.118.1.el8_62024-08-13redhat

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.

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
linux5.10.46-4, 5.10.46-5, 5.10.70-1, 5.10.70-1~bpo10+1
  • every version up to 5.10.84-1: fixed in 5.10.84-1
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.15.15-1: fixed in 5.15.15-1
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.15.15-1: fixed in 5.15.15-1
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
linux—
  • every version up to 5.15.15-1: fixed in 5.15.15-1
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 10× in last 7d / 35× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 96 of 196 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 4 repeat rows among the latest 100 are merged into the row they repeat. The 100 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-23 16:28 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  2. 2026-10-22 16:29 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  3. 2026-10-21 16:28 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  4. 2026-10-21 08:31 UTCEG score recompute
  5. 2026-10-21 08:31 UTCVendor advisory
  6. 2026-10-20 16:28 UTCEPSS rescoreEPSS 0.2% · 12th percentile
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  8. 2026-10-18 16:28 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  9. 2026-10-18 08:49 UTCEG score recompute
  10. 2026-10-17 16:29 UTCEPSS rescoreEPSS 0.2% · 12th percentile
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  15. 2026-10-12 19:05 UTCEG score recompute
  16. 2026-10-12 16:30 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  17. 2026-10-11 23:31 UTCEG score recompute
  18. 2026-10-11 13:44 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  19. 2026-10-10 23:17 UTCOSV refresh
  20. 2026-10-10 19:56 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  21. 2026-10-09 20:04 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  22. 2026-10-08 16:40 UTCEPSS rescoreEPSS 0.2% · 12th percentile
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  25. 2026-10-05 17:40 UTCEPSS rescoreEPSS 0.2% · 12th percentile
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  1. 2026-10-04 23:19 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  2. 2026-10-03 14:22 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  3. 2026-10-02 16:23 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  4. 2026-09-30 15:45 UTCEG score recompute
  5. 2026-09-30 15:00 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  6. 2026-09-29 15:15 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  7. 2026-09-28 13:47 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  8. 2026-09-26 15:54 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  9. 2026-09-26 00:21 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  10. 2026-09-24 14:00 UTCEPSS rescoreEPSS 0.2% · 12th percentile
  11. 2026-09-23 13:45 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  12. 2026-09-22 14:44 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  13. 2026-09-21 20:28 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  14. 2026-09-21 11:19 UTCOSV refresh
  15. 2026-09-20 20:13 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  16. 2026-09-19 15:38 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  17. 2026-09-18 19:24 UTCEPSS rescoreEPSS 0.2% · 14th percentile
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  21. 2026-09-12 14:57 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  22. 2026-09-11 14:49 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  23. 2026-09-11 09:33 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  24. 2026-09-08 21:57 UTCEPSS rescoreEPSS 0.2% · 13th percentile
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  27. 2026-09-05 15:25 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  28. 2026-09-04 13:57 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  29. 2026-09-02 14:09 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  30. 2026-09-02 09:14 UTCOSV refresh
  31. 2026-09-01 13:51 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  32. 2026-08-30 19:14 UTCEPSS rescoreEPSS 0.2% · 13th percentile
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  34. 2026-08-28 21:38 UTCEPSS rescoreEPSS 0.2% · 13th percentile
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  39. 2026-08-21 23:46 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  40. 2026-08-20 22:52 UTCEPSS rescoreEPSS 0.2% · 13th percentile
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  42. 2026-08-18 13:45 UTCEPSS rescoreEPSS 0.2% · 13th percentile
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  44. 2026-08-16 14:53 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  45. 2026-08-16 08:17 UTCOSV refresh
  46. 2026-08-16 02:11 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  47. 2026-08-15 01:27 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  48. 2026-08-13 21:57 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  49. 2026-08-12 13:48 UTCEPSS rescoreEPSS 0.2% · 13th percentile
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  52. 2026-08-08 16:34 UTCEPSS rescoreEPSS 0.2% · 13th percentile
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  60. 2026-08-01 04:13 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  61. 2026-08-01 02:12 UTCOSV refresh
  62. 2026-07-30 16:25 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  63. 2026-07-30 01:28 UTCEPSS rescoreEPSS 0.2% · 13th percentile
  64. 2026-07-28 15:33 UTCEPSS rescoreEPSS 0.2% · 13th percentile
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  69. 2026-07-23 02:06 UTCEG score recompute
  70. 2026-07-22 22:53 UTCEG score recompute
  71. 2026-07-22 14:06 UTCEPSS rescoreEPSS 0.2% · 13th percentile

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Frequently asked(5)

What is CVE-2021-47566?
CVE-2021-47566 is a high-severity vulnerability; its CVE record was published on May 24, 2024. In the Linux kernel, the following vulnerability has been resolved: proc/vmcore: fix clearing user buffer by properly using clear_user() To clear a user buffer we cannot simply use memset, we have to use clearuser(). With a virtio-mem device that registers a vmcorecb and has some logically…
When was the CVE record for CVE-2021-47566 published?
The CVE record for CVE-2021-47566 was published on May 24, 2024. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of September 18, 2025; the record at its source may have been updated since.
Is CVE-2021-47566 actively exploited?
CVE-2021-47566 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (12th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2021-47566?
CVE-2021-47566 has a CVSS v3 base score of 7.8 (NVD).
How do I remediate CVE-2021-47566?
A fix for CVE-2021-47566 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2021-47566 are linked in the Vendor Advisories panel on this page.

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