CVE-2021-47555

Local denial of service via VLAN refcount underflow

Published May 24, 2024 · Updated Aug 5, 2026

Denial of service in affected Linux kernel releases allows local users to hang network-device removal through VLAN device teardown. register_vlan_dev can fail before dev_hold increments the real-device reference, but vlan_dev_free still calls dev_put and drives the count below zero. Reaching the flaw requires local privileges to create and delete VLAN-backed links; successful triggering leaves unregister_netdevice in an endless wait.

CVSS severity5.5
Medium
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in affected Linux kernel releases allows local users to hang network-device removal through VLAN device teardown. register_vlan_dev can fail before dev_hold increments the real-device reference, but vlan_dev_free still calls dev_put and drives the count below zero. Reaching the flaw requires local privileges to create and delete VLAN-backed links; successful triggering leaves unregister_netdevice in an endless wait.

The record

CVE
CVE-2021-47555
Published
May 24, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-191, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 24, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=21032425c36ff85f16e72ca92193a8c401e4acd5 <f7fc72a508cf115c273a7a29350069def1041890
  2. Affected versionversion=5.10.80 <5.10.83
  3. Affected versionversion=5.14.19 <5.15
  4. Affected versionversion=5.15.3 <5.15.6
  5. Affected versionversion=5.4.160 <5.4.163
  6. Affected versionversion=563bcbae3ba233c275c244bfce2efe12938f5363 <01d9cc2dea3fde3bad6d27f464eff463496e2b00
  7. Affected versionversion=700602b662d7eaa816b1a3cb0abe7a85de358fd4 <5e44178864b38dd70b877985abd7d86fdb95f27d
  8. Affected versionversion=e04a7a84bb77f9cdf4475340fe931389bc72331c <6e800ee43218a56acc93676bbb3d93b74779e555
  9. Affected versionversion=fca96b3f852a1b369b7b2844ce357cd689879934

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=21032425c36ff85f16e72ca92193a8c401e4acd5 <f7fc72a508cf115c273a7a29350069def1041890; version=5.10.80 <5.10.83; version=5.14.19 <5.15; version=5.15.3 <5.15.6; version=5.4.160 <5.4.163; version=563bcbae3ba233c275c244bfce2efe12938f5363 <01d9cc2dea3fde3bad6d27f464eff463496e2b00; version=700602b662d7eaa816b1a3cb0abe7a85de358fd4 <5e44178864b38dd70b877985abd7d86fdb95f27d; version=e04a7a84bb77f9cdf4475340fe931389bc72331c <6e800ee43218a56acc93676bbb3d93b74779e555; version=fca96b3f852a1b369b7b2844ce357cd689879934

Published CVSS scores

4.4CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-191Integer Underflow (Wrap or Wraparound)
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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