CVE-2021-47506

HIGHNVD 7.87.8—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.8 under NVD CVSS v3. EPSS exploit probability: 0.8%, top 47% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Trending — 3 sources updated this week
7.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 7.8Exploit: None knownExposed: 0

A fix is available — apply it.

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

nfsd: fix use-after-free due to delegation race

A delegation break could arrive as soon as we've called vfs_setlease. A delegation break runs a callback which immediately (in nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we then exit nfs4_set_delegation without hashing the delegation, it will be freed as soon as the callback is done with it, without ever being removed from del_recall_lru.

Symptoms show up later as use-after-free or list corruption warnings, usually in the laundromat thread.

I suspect aba2072f4523 "nfsd: grant read delegations to clients holding writes" made this bug easier to hit, but I looked as far back as v3.0 and it looks to me it already had the same problem. So I'm not sure where the bug was introduced; it may have been there from the beginning.

CVSS v3
7.8
EG Score
7.8(medium)
EG Risk
35(Track)
EG Risk 35/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity78% × 45%
Exploitation1% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
53%
KEV
Not listed

Published

May 24, 2024

Last Modified

August 5, 2026

Advisory Details (8)

Auto-updated Aug 4, 2026
No patch confirmed yet.
generic

nfsd: fix use-after-free due to delegation race - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/148c816f10fd11df27ca6a9b3238cdd42fa72cd3
generic

nfsd: fix use-after-free due to delegation race - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/04a8d07f3d58308b92630045560799a3faa3ebce
generic

nfsd: fix use-after-free due to delegation race - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/eeb0711801f5e19ef654371b627682aed3b11373
generic

nfsd: fix use-after-free due to delegation race - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/e0759696de6851d7536efddfdd2dfed4c4df1f09
generic

nfsd: fix use-after-free due to delegation race - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/548ec0805c399c65ed66c6641be467f717833ab5
generic

nfsd: fix use-after-free due to delegation race - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/348714018139c39533c55661a0c7c990671396b4
generic

nfsd: fix use-after-free due to delegation race - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/33645d3e22720cac1e4548f8fef57bf0649536ee
generic

nfsd: fix use-after-free due to delegation race - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/2becaa990b93cbd2928292c0b669d3abb6cf06d4

Patch Availability(5)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-virtual-lts-xenial (4.4.0.268.274) @ xenial2026-05-24ubuntu
ubuntulinux-virtual-lts-xenial (4.4.0.268.302~14.04.1) @ trusty2026-05-24ubuntu
ubuntulinux-tools-aws (4.4.0.1143.140) @ trusty2026-05-24ubuntu
ubuntuoracle (5.15.0-1055) @ jammy2026-05-24ubuntu
ubuntulinux-tools-fips (4.4.0.1113.114) @ xenial2026-05-24ubuntu

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.

All Vendor Advisories

(5)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 11× in last 7d / 42× 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.

Showing the most recent 100 of 122 total refreshes for this CVE.

  1. 2026-08-07 16:24 UTCEPSS rescore
  2. 2026-08-06 13:44 UTCEPSS rescore
  3. 2026-08-05 19:15 UTCEPSS rescore
  4. 2026-08-05 09:39 UTCEG score recompute
  5. 2026-08-04 15:06 UTCEPSS rescore
  6. 2026-08-04 12:10 UTCEG score recompute
  7. 2026-08-04 10:34 UTCEPSS rescore
  8. 2026-08-04 09:49 UTCEG score recompute
  9. 2026-08-04 09:49 UTCVendor advisory
  10. 2026-08-03 10:33 UTCEPSS rescore
  11. 2026-08-02 02:24 UTCEPSS rescore
  12. 2026-08-01 04:13 UTCEPSS rescore
  13. 2026-08-01 01:42 UTCOSV refresh
  14. 2026-07-30 16:25 UTCEPSS rescore
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  21. 2026-07-23 14:16 UTCEPSS rescore
  22. 2026-07-23 02:06 UTCEG score recompute
  23. 2026-07-22 22:53 UTCEG score recompute
  24. 2026-07-22 14:06 UTCEPSS rescore
  25. 2026-07-20 17:05 UTCEPSS rescore
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  1. 2026-07-19 14:29 UTCEPSS rescore
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  5. 2026-07-16 17:00 UTCEPSS rescore
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  7. 2026-07-15 16:55 UTCEPSS rescore
  8. 2026-07-15 01:58 UTCEPSS rescore
  9. 2026-07-15 01:58 UTCEPSS rescore
  10. 2026-07-14 09:10 UTCOSV refresh
  11. 2026-07-13 22:27 UTCEPSS rescore
  12. 2026-07-13 06:11 UTCEPSS rescore
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  14. 2026-07-12 05:44 UTCEPSS rescore
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  18. 2026-07-08 15:12 UTCEPSS rescore
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  20. 2026-07-07 13:43 UTCEPSS rescore
  21. 2026-07-06 16:25 UTCEPSS rescore
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  23. 2026-07-06 02:21 UTCEPSS rescore
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  25. 2026-07-05 02:28 UTCEPSS rescore
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  27. 2026-07-04 06:29 UTCEPSS rescore
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  30. 2026-06-30 23:20 UTCEPSS rescore
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  36. 2026-06-27 03:07 UTCEPSS rescore
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  38. 2026-06-26 09:39 UTCOSV refresh
  39. 2026-06-25 13:48 UTCEPSS rescore
  40. 2026-06-25 13:48 UTCEPSS rescore
  41. 2026-06-24 14:03 UTCEPSS rescore
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  43. 2026-06-23 21:31 UTCEPSS rescore
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  45. 2026-06-22 14:24 UTCEPSS rescore
  46. 2026-06-21 14:55 UTCEPSS rescore
  47. 2026-06-21 01:58 UTCEPSS rescore
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  49. 2026-06-19 19:24 UTCEPSS rescore
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  51. 2026-06-18 17:51 UTCEPSS rescore
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  59. 2026-06-13 22:58 UTCEPSS rescore
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  63. 2026-06-10 22:16 UTCEPSS rescore
  64. 2026-06-10 13:20 UTCEPSS rescore
  65. 2026-06-08 16:41 UTCOSV refresh
  66. 2026-06-08 14:15 UTCEPSS rescore
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  75. 2026-06-05 06:09 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2021-47506?
CVE-2021-47506 is a high vulnerability published on May 24, 2024. In the Linux kernel, the following vulnerability has been resolved: nfsd: fix use-after-free due to delegation race A delegation break could arrive as soon as we've called vfs_setlease. A delegation break runs a callback which immediately (in nfsd4cbrecallprepare) adds the delegation to…
When was CVE-2021-47506 disclosed?
CVE-2021-47506 was first published in the National Vulnerability Database on May 24, 2024, with the most recent update on August 5, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-47506 actively exploited?
CVE-2021-47506 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 47.4% of all scored CVEs.
What is the CVSS score of CVE-2021-47506?
CVE-2021-47506 has a CVSS v3 base score of 7.8 (NVD).
How do I remediate CVE-2021-47506?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-47506, 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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