CVE-2021-47089

Local denial of service via unreleased KFENCE allocations

Published Mar 4, 2024 · Updated May 11, 2026

Memory leak in Linux kernel 5.12 before 5.15.12 allows local users to exhaust kernel memory by repeatedly reading KFENCE objects. The KFENCE debugfs file_operations table omits a release handler, so closing the objects file leaves seq_file and seq_buf allocations unreleased. Access requires a kernel built with KFENCE and debugfs enabled; debugfs is root-only by default, while delegated access exposes gradual availability degradation.

CVSS severity3.3
Low
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory leak in Linux kernel 5.12 before 5.15.12 allows local users to exhaust kernel memory by repeatedly reading KFENCE objects. The KFENCE debugfs file_operations table omits a release handler, so closing the objects file leaves seq_file and seq_buf allocations unreleased. Access requires a kernel built with KFENCE and debugfs enabled; debugfs is root-only by default, while delegated access exposes gradual availability degradation.

The record

CVE
CVE-2021-47089
Published
Mar 4, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-401, T1499.001
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 4, 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=0ce20dd840897b12ae70869c69f1ba34d6d16965 <0129ab1f268b6cf88825eae819b9b84aa0a85634
  2. Affected versionversion=0ce20dd840897b12ae70869c69f1ba34d6d16965 <2f06c8293d27f6337f907042c602c9c953988c48
  3. Affected versionversion=5.12

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=0ce20dd840897b12ae70869c69f1ba34d6d16965 <0129ab1f268b6cf88825eae819b9b84aa0a85634; version=0ce20dd840897b12ae70869c69f1ba34d6d16965 <2f06c8293d27f6337f907042c602c9c953988c48; version=5.12
The Linux Kernel Organization · Linux Kernelversion=0 <5.12; version=0ce20dd84089 <0129ab1f268b; version=0ce20dd84089 <2f06c8293d27; version=5.12; version=5.15.12 <=5.15*; version=5.16 <=*

Published CVSS scores

3.3CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

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

CWE-401Missing Release of Memory after Effective Lifetime
T1499.001OS Exhaustion Flood

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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