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NVD / CVE Program· CNA Linux

CVE-2021-47109: neighbour: allow NUD_NOARP entries to be forced GCed

MediumCVSS 5.5 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 22/100)

  • 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: 0.69% (FIRST EPSS); higher than 53.2% of all records.
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 7a6b1ab7475fd6478eeaf5c9d1163e7a18125c8f, d17d47da59f726dc4c87caebda3a50333d7e2fd3, d99029e6aab62aef0a0251588b2867e77e83b137.
  • Severity is disputed: the assigning authority (CNA) scores it 7.5, NVD 5.5.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 7a6b1ab7475fd6478eeaf5c9d1163e7a18125c8f, d17d47da59f726dc4c87caebda3a50333d7e2fd3, d99029e6aab62aef0a0251588b2867e77e83b137 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: neighbour: allow NUD_NOARP entries to be forced GCed IFF_POINTOPOINT interfaces use NUD_NOARP entries for IPv6. It's possible to fill up the neighbour table with enough entries that it will overflow for valid connections after that. This behaviour is more prevalent after commit 58956317c8de ("neighbor: Improve garbage collection") is applied, as it prevents removal from entries that are not NUD_FAILED, unless they are more than 5s old.

Published
Mar 15, 2024
Updated
Aug 5, 2026
EPSS
0.6% · 53th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.6%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
5.5
CNA · Linux
7.5
2.0 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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-2021-47109

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

    • 5.0affected
    • 58956317c8de52009d1a38a721474c24aef74fe7 and later · before d99029e6aab62aef0a0251588b2867e77e83b137affected · git
    • 58956317c8de52009d1a38a721474c24aef74fe7 and later · before d17d47da59f726dc4c87caebda3a50333d7e2fd3affected · git
    • 58956317c8de52009d1a38a721474c24aef74fe7 and later · before ddf088d7aaaaacfc836104f2e632b29b1d383cfcaffected · git
    • 58956317c8de52009d1a38a721474c24aef74fe7 and later · before 7a6b1ab7475fd6478eeaf5c9d1163e7a18125c8faffected · git
    • before 5.0not affected · semver
    • 5.4.125 and later · up to and including 5.4.*not affected · semver
    • 5.10.43 and later · up to and including 5.10.*not affected · semver
    • 5.12.10 and later · up to and including 5.12.*not affected · semver
    • 5.13 and laternot affected · original_commit_for_fix
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 kernel5.0 and later · before 5.4.125
  • linux linux kernel5.5 and later · before 5.10.43
  • linux linux kernel5.11 and later · before 5.12.10
  • linux linux kernel5.13

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 5.10.46-15.10.46-1

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-2024-26630Mar 13, 2024 · mm: cachestat: fix folio read-after-free in cache walk
    28Monitor
  • ← EarlierCVE-2024-26629Mar 13, 2024 · nfsd: fix RELEASE_LOCKOWNER
    22Monitor
  • Later →CVE-2021-47110Mar 15, 2024 · x86/kvm: Disable kvmclock on all CPUs on shutdown
    28Monitor

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 Linux7a6b1ab7475fd6478eeaf5c9d1163e7a18125c8fVendor (CNA)
Linux Linuxd17d47da59f726dc4c87caebda3a50333d7e2fd3Vendor (CNA)
Linux Linuxd99029e6aab62aef0a0251588b2867e77e83b137Vendor (CNA)
Linux Linuxddf088d7aaaaacfc836104f2e632b29b1d383cfcVendor (CNA)
debian:linux5.10.46-1 · 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.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2023-0179354 days apartA buffer overflow vulnerability was found in the Netfilter subsystem in the Linux Kernel.
    32Monitor
  • CVE-2021-4709811 days aparthwmon: (lm90) Prevent integer overflow/underflow in hysteresis calculations
    31Monitor
  • CVE-2024-2330750 days apartInteger overflow in raid5_cache_count in Linux kernel
    31Monitor
  • CVE-2024-40994119 days apartptp: fix integer overflow in max_vclocks_store
    31Monitor
  • CVE-2024-41000119 days apartblock/ioctl: prefer different overflow check
    31Monitor
  • CVE-2022-48837123 days apartusb: gadget: rndis: prevent integer overflow in rndis_set_response()
    31Monitor

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 · 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.
  • No special conditions are required; it is repeatable.

If successful

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

Weakness class (CWE)

CWE-190 · Integer Overflow or Wraparound

CVSS vector

CVSS:3.1/AV:L/AC:L/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