CVE-2021-47509

Local service interruption via oversized PCM period

Published May 24, 2024 · Updated May 11, 2026

Memory exhaustion in the Linux kernel ALSA OSS PCM layer allows local users to interrupt service via an oversized fragment shift. The SNDCTL_DSP_SETFRAGMENT ioctl permits a fragment shift of up to 31 bits to drive period-size calculations in sound/core/oss/pcm_oss.c, causing temporary buffers to be allocated at attacker-controlled sizes. A low-privileged user must reach the OSS PCM device interface; exhausting kernel memory can hang or crash the host.

CVSS severity5.5
Medium
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

Memory exhaustion in the Linux kernel ALSA OSS PCM layer allows local users to interrupt service via an oversized fragment shift. The SNDCTL_DSP_SETFRAGMENT ioctl permits a fragment shift of up to 31 bits to drive period-size calculations in sound/core/oss/pcm_oss.c, causing temporary buffers to be allocated at attacker-controlled sizes. A low-privileged user must reach the OSS PCM device interface; exhausting kernel memory can hang or crash the host.

The record

CVE
CVE-2021-47509
Published
May 24, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 24, 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=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <2e54cf6794bf82a54aaefc78da13819aea9cd28a
  2. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <35a3e511032146941085f87dd9fb5b82ea5c00a2
  3. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <76f19e4cbb548e28547f8c328aa0bfb3a10222d3
  4. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <8839c8c0f77ab8fc0463f4ab8b37fca3f70677c2
  5. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <ad45babf7886e7a212ee1d5eda9ef49f696db43c
  6. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <b02a41eebcc36d4f07196780f2e165ca2c499257
  7. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <be55f306396cd62c6889286a7194fd8b53363aeb
  8. Affected versionversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <d1bb703ad050de9095f10b2d3416c32921ac6bcc
  9. Affected versionversion=2.6.12

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <2e54cf6794bf82a54aaefc78da13819aea9cd28a; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <35a3e511032146941085f87dd9fb5b82ea5c00a2; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <76f19e4cbb548e28547f8c328aa0bfb3a10222d3; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <8839c8c0f77ab8fc0463f4ab8b37fca3f70677c2; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <ad45babf7886e7a212ee1d5eda9ef49f696db43c; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <b02a41eebcc36d4f07196780f2e165ca2c499257; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <be55f306396cd62c6889286a7194fd8b53363aeb; version=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <d1bb703ad050de9095f10b2d3416c32921ac6bcc; version=2.6.12

Published CVSS scores

5.5CISA-ADPCVSS: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

No sourced classifications are available.

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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