CVE-2021-3348

System crash via unlocked NBD socket reallocation

Published Feb 1, 2021 · Updated Aug 3, 2024

Use-after-free in the Linux kernel NBD driver through 5.10.12 allows local users with device access to crash the system via an I/O request. During device setup, nbd_add_socket invokes krealloc on config->socks while nbd_queue_rq and nbd_handle_cmd read that array without locking. Access to an NBD device and precise ioctl and I/O timing are required; the stale-pointer read can crash the kernel, while arbitrary code execution is vendor-rated as possible rather than confirmed.

CVSS severity7.0
High
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

Use-after-free in the Linux kernel NBD driver through 5.10.12 allows local users with device access to crash the system via an I/O request. During device setup, nbd_add_socket invokes krealloc on config->socks while nbd_queue_rq and nbd_handle_cmd read that array without locking. Access to an NBD device and precise ioctl and I/O timing are required; the stale-pointer read can crash the kernel, while arbitrary code execution is vendor-rated as possible rather than confirmed.

The record

CVE
CVE-2021-3348
Published
Feb 1, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.4National Vulnerability DatabaseAV:L/AC:M/Au:N/C:P/I:P/A:P
5.1SUSECVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
7.0Canonical UbuntuCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/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)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1068Exploitation for Privilege Escalation

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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