CVE-2021-47439

Kernel crash via rescheduled KSZ workqueue

Published May 22, 2024 · Updated May 11, 2026

NULL pointer dereference in the Microchip KSZ DSA driver in Linux allows local users to crash the kernel during module removal. The ksz_switch_remove path cancels mib_read_work before DSA teardown, but ksz_mac_link_down reschedules it while mib_interval remains nonzero; the delayed work then dereferences the unregistered dp->slave. Reaching the flaw requires a loaded KSZ switch driver and CAP_SYS_MODULE privilege to unload it, and exploitation interrupts the host without reported data disclosure or modification.

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

NULL pointer dereference in the Microchip KSZ DSA driver in Linux allows local users to crash the kernel during module removal. The ksz_switch_remove path cancels mib_read_work before DSA teardown, but ksz_mac_link_down reschedules it while mib_interval remains nonzero; the delayed work then dereferences the unregistered dp->slave. Reaching the flaw requires a loaded KSZ switch driver and CAP_SYS_MODULE privilege to unload it, and exploitation interrupts the host without reported data disclosure or modification.

The record

CVE
CVE-2021-47439
Published
May 22, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-476, T1499
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. May 22, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 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=469b390e1ba330e888175e55d78573db2e9a8cb4 <383239a33cf29ebee9ce0d4e0e5c900b77a16148
  2. Affected versionversion=469b390e1ba330e888175e55d78573db2e9a8cb4 <ef1100ef20f29aec4e62abeccdb5bdbebba1e378
  3. Affected versionversion=469b390e1ba330e888175e55d78573db2e9a8cb4 <f2e1de075018cf71bcd7d628e9f759cb8540b0c3
  4. Affected versionversion=5.7

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linuxversion=469b390e1ba330e888175e55d78573db2e9a8cb4 <383239a33cf29ebee9ce0d4e0e5c900b77a16148; version=469b390e1ba330e888175e55d78573db2e9a8cb4 <ef1100ef20f29aec4e62abeccdb5bdbebba1e378; version=469b390e1ba330e888175e55d78573db2e9a8cb4 <f2e1de075018cf71bcd7d628e9f759cb8540b0c3; version=5.7

Published CVSS scores

5.5CISA-ADPCVSS: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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