LiveActive security incident?Get immediate response
CVE Record

CVE-2021-47509: ALSA: pcm: oss: Limit the period size to 16MB

In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: oss: Limit the period size to 16MB Set the practical limit to the period size (the fragment shift in OSS) instead of a full 31bit; a too large value could lead to the exhaust of memory as we allocate temporary buffers of the period size, too. As of this patch, we set to 16MB limit, which should cover all use cases.

MediumCVSS 5.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-47509 is a local Linux kernel denial-of-service issue in ALSA OSS PCM handling. A local user could request an oversized audio period buffer, causing excessive memory allocation and system availability impact. The upstream fix caps the practical period size at 16MB.

Executive priority

Treat as a moderate patching item. It is most relevant for multi-user Linux systems because exploitation requires local privileges, but successful abuse can affect system availability.

Technical view

The ALSA pcm_oss path accepted a very large fragment shift, effectively allowing period sizes up to a 31-bit range. Temporary buffers are allocated at period size, so oversized values could exhaust memory. The patch limits the period size to 16MB.

Likely exposure

Exposure is mainly Linux systems running affected kernels where local users can access ALSA OSS PCM functionality. The CVSS vector is local, low complexity, low privileges, no user interaction, and availability-only impact.

Exploitation context

The source bundle does not show CISA KEV listing or active exploitation. This is not described as remote code execution; the supported risk is local availability impact through memory exhaustion.

Researcher notes

Affected-version data in the bundle is broad and upstream-oriented. Use distribution backport status, not only kernel version strings, to decide exposure. The referenced stable commits are the primary remediation evidence.

Mitigation direction

  • Update to a vendor kernel containing the referenced upstream stable fix.
  • Prioritize shared systems with untrusted local users or shell access.
  • Check distribution advisories for exact fixed package versions.
  • If vendor-supported, disable unused OSS PCM compatibility until patched.

Validation and detection

  • Inventory Linux kernel versions against vendor fixed-version guidance.
  • Confirm the running kernel includes the ALSA pcm_oss 16MB period-size limit.
  • Review whether local users can access affected audio interfaces.
  • Validate patched systems through normal audio regression testing.
Prepared
Confidence
high
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-47509 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
2ADP providers
9Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.5CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H1.83.6CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

5.5Medium
CVSS 3.1 vector shape for CVE-2021-47509Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2unaffected
LinuxLinux2.6.12, 0, 4.4.295, 4.9.293, 4.14.258, 4.19.221, 5.4.165, 5.10.85, 5.15.8, 5.16affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.