CVE-2021-47281

Local kernel compromise via ALSA timer race

Published May 21, 2024 · Updated Aug 5, 2026

Use-after-free in the Linux kernel ALSA sequencer allows local users to corrupt kernel memory through concurrent timer operations. snd_seq_timer_open checks for an existing queue timer without synchronization, so a concurrent call can replace tmr->timeri and leave the old timer running after the queue is freed. A low-privilege user with access to the ALSA sequencer device can trigger the race, causing a kernel crash or compromise of kernel memory.

CVSS severity7.0
High
EPSS probability0.24%
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 ALSA sequencer allows local users to corrupt kernel memory through concurrent timer operations. snd_seq_timer_open checks for an existing queue timer without synchronization, so a concurrent call can replace tmr->timeri and leave the old timer running after the queue is freed. A low-privilege user with access to the ALSA sequencer device can trigger the race, causing a kernel crash or compromise of kernel memory.

The record

CVE
CVE-2021-47281
Published
May 21, 2024
Updated
Aug 5, 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. Aug 5, 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=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <536a7646c00a0f14fee49e5e313109e5da2f6031
  2. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <83e197a8414c0ba545e7e3916ce05f836f349273
  3. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <bd7d88b0874f82f7b29d1a53e574cedaf23166ba
  4. Affected versionversion=2.6.12

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <536a7646c00a0f14fee49e5e313109e5da2f6031; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <83e197a8414c0ba545e7e3916ce05f836f349273; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <bd7d88b0874f82f7b29d1a53e574cedaf23166ba; version=2.6.12

Published CVSS scores

5.8Amazon LinuxCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
7.0NIST NVDCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
5.5SUSECVSS:3.1/AV:L/AC:L/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

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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