CVE-2021-47379

Kernel memory corruption via unlocked BFQ teardown

Published May 21, 2024 · Updated May 23, 2026

Use-after-free in the Linux kernel's blk-cgroup code allows local users to corrupt kernel memory by racing BFQ policy teardown. blkcg_deactivate_policy frees per-policy blkg data without first taking the associated blkcg lock, so bfq_io_set_weight_legacy can read that data after release. Triggering the race requires low-privilege local access to cgroup and I/O-scheduler control paths; the observed result is an invalid kernel read, while code execution was not demonstrated.

CVSS severity7.8
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's blk-cgroup code allows local users to corrupt kernel memory by racing BFQ policy teardown. blkcg_deactivate_policy frees per-policy blkg data without first taking the associated blkcg lock, so bfq_io_set_weight_legacy can read that data after release. Triggering the race requires low-privilege local access to cgroup and I/O-scheduler control paths; the observed result is an invalid kernel read, while code execution was not demonstrated.

The record

CVE
CVE-2021-47379
Published
May 21, 2024
Updated
May 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 21, 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=3ca6e949b751fa3dfbf475ce635364cef543738b
  2. Affected versionversion=4.14.51 <4.15
  3. Affected versionversion=4.16.17 <4.17
  4. Affected versionversion=4.17
  5. Affected versionversion=946b81da114b8ba5c74bb01e57c0c6eca2bdc801 <7c2c69e010431b0157c9454adcdd2305809bf9fb
  6. Affected versionversion=946b81da114b8ba5c74bb01e57c0c6eca2bdc801 <858560b27645e7e97aca37ee8f232cccd658fbd2
  7. Affected versionversion=946b81da114b8ba5c74bb01e57c0c6eca2bdc801 <d12ddd843f1877de1f7dd2aeea4907cf9ff3ac08
  8. Affected versionversion=946b81da114b8ba5c74bb01e57c0c6eca2bdc801 <f58d305887ad7b24986d58e881f6806bb81b2bdf
  9. Affected versionversion=9d5e2d69705fed4ab527f5a283b90ae602f4e0fd

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=3ca6e949b751fa3dfbf475ce635364cef543738b; version=4.14.51 <4.15; version=4.16.17 <4.17; version=4.17; version=946b81da114b8ba5c74bb01e57c0c6eca2bdc801 <7c2c69e010431b0157c9454adcdd2305809bf9fb; version=946b81da114b8ba5c74bb01e57c0c6eca2bdc801 <858560b27645e7e97aca37ee8f232cccd658fbd2; version=946b81da114b8ba5c74bb01e57c0c6eca2bdc801 <d12ddd843f1877de1f7dd2aeea4907cf9ff3ac08; version=946b81da114b8ba5c74bb01e57c0c6eca2bdc801 <f58d305887ad7b24986d58e881f6806bb81b2bdf; version=9d5e2d69705fed4ab527f5a283b90ae602f4e0fd

Published CVSS scores

7.8UbuntuCVSS:3.1/AV:L/AC:L/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.

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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

T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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