CVE-2021-20321

Local system crash via missing negative dentry check

Published Feb 18, 2022 · Updated Aug 3, 2024

Race condition in Linux Kernel OverlayFS 5.15-rc5 allows local users to crash the system through a crafted rename operation. The ovl_rename function passes a negative target dentry to vfs_rename without first rejecting that invalid state, creating a race over the file object. Exploitation requires low-privileged local access and an OverlayFS mount; the documented consequence is a system crash, not data disclosure or modification.

CVSS severity4.7
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

Race condition in Linux Kernel OverlayFS 5.15-rc5 allows local users to crash the system through a crafted rename operation. The ovl_rename function passes a negative target dentry to vfs_rename without first rejecting that invalid state, creating a race over the file object. Exploitation requires low-privileged local access and an OverlayFS mount; the documented consequence is a system crash, not data disclosure or modification.

The record

CVE
CVE-2021-20321
Published
Feb 18, 2022
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-362, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 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 5.15-rc5

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=kernel 5.15-rc5

Published CVSS scores

4.7NVDCVSS:3.1/AV:L/AC:H/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-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
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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