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NVD / CVE Program· CNA Linux

CVE-2021-47507: nfsd: Fix nsfd startup race (again)

MediumCVSS 4.7 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 18/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.18% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. Special conditions such as timing or configuration are required.
  • Fixed version: Linux Linux 5.10.85, 5.12, 5.4.165.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 5.10.85, 5.12, 5.4.165 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: nfsd: Fix nsfd startup race (again) Commit bd5ae9288d64 ("nfsd: register pernet ops last, unregister first") has re-opened rpc_pipefs_event() race against nfsd_net_id registration (register_pernet_subsys()) which has been fixed by commit bb7ffbf29e76 ("nfsd: fix nsfd startup race triggering BUG_ON"). Restore the order of register_pernet_subsys() vs register_cld_notifier(). Add WARN_ON() to prevent a future regression. Crash info: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000012 CPU: 8 PID: 345 Comm: mount Not tainted 5.4.144-... #1 pc : rpc_pipefs_event+0x54/0x120 [nfsd] lr : rpc_pipefs_event+0x48/0x120 [nfsd] Call trace: rpc_pipefs_event+0x54/0x120 [nfsd] blocking_notifier_call_chain rpc_fill_super get_tree_keyed rpc_fs_get_tree vfs_get_tree do_mount ksys_mount __arm64_sys_mount el0_svc_handler el0_svc

Published
May 24, 2024
Updated
Jun 17, 2026
EPSS
0.1% · 8th percentile

Report tools

JSON

Action score

18

Monitor

Low priority for now.

CVSS
18 / 40 · 4.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-47507

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 4d41f65efeec0a6da6088341203c81e49ebfcd90, 5.12affected
    • 8677e99150b0830d29cc1318b4cc559e176940bb and later · before f5734b1714ca355703e9ea8fb61d04beff1790b9affected · git
    • 7c7cb07d4affcf41749234fe9dc4d90cd3959e32 and later · before c520943a00ad5015704969ad3304c956bcd49d25affected · git
    • bd5ae9288d6451bd346a1b4a59d4fe7e62ba29b7 and later · before 8bf902fee5893cfc2f04a698abab47629699ae9aaffected · git
    • bd5ae9288d6451bd346a1b4a59d4fe7e62ba29b7 and later · before b10252c7ae9c9d7c90552f88b544a44ee773af64affected · git
    • 5.4.102 and later · before 5.4.165affected · semver
    • 5.10.20 and later · before 5.10.85affected · semver
    • 5.11.3 and later · before 5.12affected · semver
    • before 5.12not affected · semver
    • 5.4.165 and later · up to and including 5.4.*not affected · semver
Affected versions · NVD (4)

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel5.4.102 and later · before 5.4.165
  • linux linux kernel5.10.20 and later · before 5.10.85
  • linux linux kernel5.11.3 and later · before 5.15.8
  • linux linux kernel5.16

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 5.15.15-15.15.15-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe…KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2021-47505May 24, 2024 · aio: fix use-after-free due to missing POLLFREE handling
    31Monitor
  • ← EarlierCVE-2021-47506May 24, 2024 · nfsd: fix use-after-free due to delegation race
    31Monitor
  • Later →CVE-2021-47508May 24, 2024 · btrfs: free exchange changeset on failures
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux5.10.85Vendor (CNA)
Linux Linux5.12Vendor (CNA)
Linux Linux5.4.165Vendor (CNA)
Linux Linux8bf902fee5893cfc2f04a698abab47629699ae9aVendor (CNA)
Linux Linuxb10252c7ae9c9d7c90552f88b544a44ee773af64Vendor (CNA)
Linux Linuxc520943a00ad5015704969ad3304c956bcd49d25Vendor (CNA)
Linux Linuxf5734b1714ca355703e9ea8fb61d04beff1790b9Vendor (CNA)
debian:linux5.15.15-1 · Debian:12Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-362 · Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

CVSS vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

References

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records