CVE-2021-46981

Local kernel crash via null NBD workqueue

Published Feb 28, 2024 · Updated May 23, 2026

NULL pointer dereference in the Linux kernel NBD driver allows local users to crash the kernel through an NBD disconnect request. The nbd_disconnect_and_put function passes recv_workq to flush_workqueue after an incompletely configured device leaves that pointer NULL. Access to open an NBD device and send its generic-netlink disconnect command is required; the demonstrated result is a kernel oops and service interruption.

CVSS severity5.5
Medium
EPSS probability0.25%
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 Linux kernel NBD driver allows local users to crash the kernel through an NBD disconnect request. The nbd_disconnect_and_put function passes recv_workq to flush_workqueue after an incompletely configured device leaves that pointer NULL. Access to open an NBD device and send its generic-netlink disconnect command is required; the demonstrated result is a kernel oops and service interruption.

The record

CVE
CVE-2021-46981
Published
Feb 28, 2024
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-476, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 28, 2024CVE publishedPublication date reported by the CVE source.
  2. May 23, 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=0b584bf573ae59021069c056c22d65d5721910cb
  2. Affected versionversion=4.14.149 <4.15
  3. Affected versionversion=4.19.79 <4.20
  4. Affected versionversion=5.3.6 <5.4
  5. Affected versionversion=5.4
  6. Affected versionversion=92ec11cccb7fc14331e000ab2337f60aa433433e
  7. Affected versionversion=9f0f39c92e4f50189155dfb13bb5524372e40eba
  8. Affected versionversion=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <1c4962df938891af9ab4775f5224ef8601764107
  9. Affected versionversion=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <54b78ba7e96e5fe1edb8054e375d31a6c0dc60dc
  10. Affected versionversion=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <79ebe9110fa458d58f1fceb078e2068d7ad37390
  11. Affected versionversion=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <b31d237796fd618379ec8e0f4de3370b5e4aeee7
  12. Affected versionversion=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <cde4b55cfb24522dcbba80bbdb0c082303e76c43

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=0b584bf573ae59021069c056c22d65d5721910cb; version=4.14.149 <4.15; version=4.19.79 <4.20; version=5.3.6 <5.4; version=5.4; version=92ec11cccb7fc14331e000ab2337f60aa433433e; version=9f0f39c92e4f50189155dfb13bb5524372e40eba; version=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <1c4962df938891af9ab4775f5224ef8601764107; version=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <54b78ba7e96e5fe1edb8054e375d31a6c0dc60dc; version=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <79ebe9110fa458d58f1fceb078e2068d7ad37390; version=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <b31d237796fd618379ec8e0f4de3370b5e4aeee7; version=e9e006f5fcf2bab59149cb38a48a4817c1b538b4 <cde4b55cfb24522dcbba80bbdb0c082303e76c43

Published CVSS scores

5.5NVDCVSS: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-476NULL Pointer Dereference
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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