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CVE Record

CVE-2021-47556: ethtool: ioctl: fix potential NULL deref in ethtool_set_coalesce()

In the Linux kernel, the following vulnerability has been resolved: ethtool: ioctl: fix potential NULL deref in ethtool_set_coalesce() ethtool_set_coalesce() now uses both the .get_coalesce() and .set_coalesce() callbacks. But the check for their availability is buggy, so changing the coalesce settings on a device where the driver provides only _one_ of the callbacks results in a NULL pointer dereference instead of an -EOPNOTSUPP. Fix the condition so that the availability of both callbacks is ensured. This also matches the netlink code. Note that reproducing this requires some effort - it only affects the legacy ioctl path, and needs a specific combination of driver options: - have .get_coalesce() and .coalesce_supported but no .set_coalesce(), or - have .set_coalesce() but no .get_coalesce(). Here eg. ethtool doesn't cause the crash as it first attempts to call ethtool_get_coalesce() and bails out on error.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel bug that can crash the system when legacy ethtool ioctl coalescing settings are changed on certain network drivers. It is not described as remote code execution. The source says reproduction requires effort and a specific driver callback mismatch.

Executive priority

Treat this as a stability and availability issue, not a confirmed active-exploitation emergency. Patch during normal kernel maintenance, faster for high-availability systems where an unexpected kernel crash would create business impact.

Technical view

ethtool_set_coalesce() can dereference a NULL callback because it did not correctly require both get_coalesce() and set_coalesce(). The issue affects the legacy ioctl path when driver callback support is incomplete. The fix changes the condition to ensure both callbacks exist, matching the netlink path behavior.

Likely exposure

Exposure is most likely on Linux systems running affected 5.15-era kernels with network drivers matching the callback combinations described in the CVE. Systems not using the legacy ioctl path or not exposing affected driver behavior are less likely to be impacted.

Exploitation context

The provided sources do not show active exploitation, and CISA KEV is false. The CVE text says reproduction requires effort, affects only the legacy ioctl path, and depends on specific driver options. Expected impact is a local or operational denial of service through kernel NULL dereference.

Researcher notes

The key exposure condition is driver-specific callback asymmetry in ethtool coalesce handling. Validate against actual driver implementations and the ioctl path. The sources do not provide CVSS, CWE, exploit reports, or distribution-specific fixed versions.

Mitigation direction

  • Apply Linux kernel updates containing the referenced stable fixes.
  • Check distribution vendor advisories for the exact fixed kernel package.
  • Avoid changing affected coalesce settings through legacy ioctl paths until patched.
  • Prioritize shared, production, and remotely managed network hosts.

Validation and detection

  • Inventory Linux kernel versions against the CVE affected range.
  • Review whether network drivers implement only one ethtool coalesce callback.
  • Confirm patched kernels include the referenced stable commits.
  • Check crash logs for NULL dereference near ethtool_set_coalesce().
Prepared
Confidence
high
Sources
4

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

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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
3Source 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

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxf3ccfda1931977b80267ba54070a1aeafa18f6ca, f3ccfda1931977b80267ba54070a1aeafa18f6caunaffected
LinuxLinux5.15, 0, 5.15.6, 5.16affected
Weakness

CWE details

No CWE listed

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