CVE-2021-47559Network attack vector

Remote host crash via SMC NULL dereference

Published May 24, 2024 · Updated Aug 5, 2026

A NULL pointer dereference in Linux kernel SMC allows remote attackers to crash the host through a crafted CLC handshake over TCP. smc_vlan_by_tcpsk passes a NULL result from netdev_lower_get_next to is_vlan_dev while manually walking lower network devices. The trigger requires an AF_SMC listener and a stacked lower-device topology; the dereference causes a kernel oops or panic.

CVSS severity7.5
High
EPSS probability0.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A NULL pointer dereference in Linux kernel SMC allows remote attackers to crash the host through a crafted CLC handshake over TCP. smc_vlan_by_tcpsk passes a NULL result from netdev_lower_get_next to is_vlan_dev while manually walking lower network devices. The trigger requires an AF_SMC listener and a stacked lower-device topology; the dereference causes a kernel oops or panic.

The record

CVE
CVE-2021-47559
Published
May 24, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-476, T1499.004
Attack vector
network
Privileges
unauthenticated

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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=4.18
  2. Affected versionversion=cb9d43f6775457cac75544bc4197f26ac2b6f294 <587acad41f1bc48e16f42bb2aca63bf323380be8
  3. Affected versionversion=cb9d43f6775457cac75544bc4197f26ac2b6f294 <bb851d0fb02547d03cd40106b5f2391c4fed6ed1
  4. Affected versionversion=cb9d43f6775457cac75544bc4197f26ac2b6f294 <c94cbd262b6aa3b54d73a1ed1f9c0d19df57f4ff

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.18; version=cb9d43f6775457cac75544bc4197f26ac2b6f294 <587acad41f1bc48e16f42bb2aca63bf323380be8; version=cb9d43f6775457cac75544bc4197f26ac2b6f294 <bb851d0fb02547d03cd40106b5f2391c4fed6ed1; version=cb9d43f6775457cac75544bc4197f26ac2b6f294 <c94cbd262b6aa3b54d73a1ed1f9c0d19df57f4ff

Published CVSS scores

7.5kernel.orgCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

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

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499.004Application or System Exploitation

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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