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CVE Record

CVE-2021-46966: ACPI: custom_method: fix potential use-after-free issue

In the Linux kernel, the following vulnerability has been resolved: ACPI: custom_method: fix potential use-after-free issue In cm_write(), buf is always freed when reaching the end of the function. If the requested count is less than table.length, the allocated buffer will be freed but subsequent calls to cm_write() will still try to access it. Remove the unconditional kfree(buf) at the end of the function and set the buf to NULL in the -EINVAL error path to match the rest of function.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This Linux kernel issue is a memory-safety bug in ACPI custom_method handling. A write path could free an internal buffer while later writes still expected it to be valid. The public record does not provide CVSS, impact detail, or active exploitation evidence, so urgency depends on whether affected kernels are present in your fleet.

Executive priority

Treat this as a patch-management item until more impact evidence appears. It does not have KEV status or a published severity in the provided sources, but kernel memory-safety flaws should be cleared during normal or accelerated Linux maintenance cycles.

Technical view

In cm_write(), buf was always freed at function exit. When count was less than table.length, the buffer could be freed while subsequent cm_write() calls still referenced it, creating a potential use-after-free. The fix removes the unconditional kfree(buf) and sets buf to NULL on the -EINVAL path.

Likely exposure

Exposure is limited to Linux systems running affected kernel versions listed in the CVE data, including several 4.4 through 5.13-era stable lines. Distribution backports may change package-level exposure, so validate by vendor kernel advisory or source patch status, not version strings alone.

Exploitation context

The provided sources do not claim exploitation in the wild, and the CVE is not marked KEV. No public source bundle evidence describes exploitability, required privileges, or reachable attack surface beyond the affected ACPI custom_method write logic.

Researcher notes

Key unknowns are practical reachability, privilege requirements, and consequence after use-after-free. Analysis should focus on whether ACPI custom_method is compiled and exposed in target kernels, and whether distribution kernels have backported the stable commits without changing upstream version numbers.

Mitigation direction

  • Update affected Linux kernels through supported vendor or distribution channels.
  • Confirm the update includes one of the referenced stable kernel fixes.
  • If immediate patching is unavailable, check vendor guidance for supported interim mitigations.
  • Prioritize systems where local users or workloads can reach ACPI debug interfaces.

Validation and detection

  • Inventory Linux kernel versions and distribution package revisions across affected assets.
  • Check vendor advisories for backported fixes matching CVE-2021-46966.
  • Validate source or package changelog includes the cm_write() buffer lifetime fix.
  • Confirm no unsupported affected kernel branches remain in production.
Prepared
Confidence
medium
Sources
11

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

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CVE-2021-46966 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
3Timeline events
2ADP providers
10Source links

SSVC decision data

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

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
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux4bda2b79a9d04c8ba31681c66e95877dbb433416, 5c12dadcbef8cd55ef1f5dac799bfcbb7ea7db1d, 35b88a10535edcf62d3e6b7893a8cd506ff98a24, e4467fb6ef547aa352dc03397f9474ec84eced5b, 03d1571d9513369c17e6848476763ebbd10ec2cb, 03d1571d9513369c17e6848476763ebbd10ec2cb, 03d1571d9513369c17e6848476763ebbd10ec2cb, 03d1571d9513369c17e6848476763ebbd10ec2cb, 03d1571d9513369c17e6848476763ebbd10ec2cb, 70424999fbf1f160ade111cb9baab51776e0f9c2, 06cd4a06eb596a888239fb8ceb6ea15677cab396unaffected
LinuxLinux5.4, 0, 4.4.269, 4.9.269, 4.14.233, 4.19.191, 5.4.118, 5.10.36, 5.11.20, 5.12.3, 5.13affected
Weakness

CWE details

No CWE listed

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