CVE-2021-4083

Local privilege escalation via stale file reference

Published Jan 18, 2022 · Updated Aug 3, 2024

Use-after-free in Unix domain socket garbage collection in Linux Kernel before 5.16-rc4 allows local users to crash or gain privileges. Lockless fget() lookup can acquire a reference after concurrent close() removes the descriptor, causing garbage collection to misclassify a file with a renewed reference. A local process must win the high-complexity race; successful exploitation can crash the system or execute code with elevated privileges.

CVSS severity7.4
High
EPSS probability0.31%
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 Unix domain socket garbage collection in Linux Kernel before 5.16-rc4 allows local users to crash or gain privileges. Lockless fget() lookup can acquire a reference after concurrent close() removes the descriptor, causing garbage collection to misclassify a file with a renewed reference. A local process must win the high-complexity race; successful exploitation can crash the system or execute code with elevated privileges.

The record

CVE
CVE-2021-4083
Published
Jan 18, 2022
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-416, CWE-362, T1068, T1499
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 18, 2022CVE 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?

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

  1. Affected versionversion=kernel 5.16-rc4

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=kernel 5.16-rc4

Published CVSS scores

7.0NVDCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
7.4Red HatCVSS:3.1/AV:L/AC:H/PR:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1068Exploitation for Privilege Escalation
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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