CVE-2020-12657

Kernel crash or code execution via BFQ race

Published May 5, 2020 · Updated Aug 4, 2024

Use-after-free in the Linux kernel before 5.6.5 allows local users to crash the system or execute arbitrary code through the BFQ scheduler. bfq_idle_slice_timer reads bfqd->in_service_queue outside bfqd-lock, allowing expiration to free the queue before bfq_idle_slice_timer_body dereferences it. A local low-privileged user must groom memory and win the BFQ scheduler race; successful triggering crashes the kernel or escalates privileges.

CVSS severity7.8
High
EPSS probability0.71%
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 before 5.6.5 allows local users to crash the system or execute arbitrary code through the BFQ scheduler. bfq_idle_slice_timer reads bfqd->in_service_queue outside bfqd-lock, allowing expiration to free the queue before bfq_idle_slice_timer_body dereferences it. A local low-privileged user must groom memory and win the BFQ scheduler race; successful triggering crashes the kernel or escalates privileges.

The record

CVE
CVE-2020-12657
Published
May 5, 2020
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-416, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 5, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.0Amazon LinuxCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P

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-416Use After Free
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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