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CVE Record

CVE-2021-47559: net/smc: Fix NULL pointer dereferencing in smc_vlan_by_tcpsk()

In the Linux kernel, the following vulnerability has been resolved: net/smc: Fix NULL pointer dereferencing in smc_vlan_by_tcpsk() Coverity reports a possible NULL dereferencing problem: in smc_vlan_by_tcpsk(): 6. returned_null: netdev_lower_get_next returns NULL (checked 29 out of 30 times). 7. var_assigned: Assigning: ndev = NULL return value from netdev_lower_get_next. 1623 ndev = (struct net_device *)netdev_lower_get_next(ndev, &lower); CID 1468509 (#1 of 1): Dereference null return value (NULL_RETURNS) 8. dereference: Dereferencing a pointer that might be NULL ndev when calling is_vlan_dev. 1624 if (is_vlan_dev(ndev)) { Remove the manual implementation and use netdev_walk_all_lower_dev() to iterate over the lower devices. While on it remove an obsolete function parameter comment.

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 possible NULL pointer dereference in the SMC networking code. In business terms, the available evidence points to reliability risk rather than confirmed data theft or takeover. Severity is not provided, and active exploitation is not reported in the supplied sources.

Executive priority

Treat this as a kernel maintenance item with targeted prioritization for SMC-enabled Linux systems. It should not outrank vulnerabilities with confirmed exploitation, but it should be included in regular kernel patch cycles because NULL dereferences can affect system availability.

Technical view

smc_vlan_by_tcpsk() manually iterated lower network devices and could pass a NULL net_device pointer to is_vlan_dev(). The fix replaces that manual walk with netdev_walk_all_lower_dev(). The record lists affected Linux kernel versions including 4.18, 5.10.83, 5.15.6, and 5.16.

Likely exposure

Exposure appears limited to Linux systems on affected kernels where the net/smc code path and lower-device or VLAN handling are relevant. The source bundle does not identify affected distributions, required kernel configuration, privilege requirements, or remote reachability.

Exploitation context

No active exploitation is indicated. The CVE is not marked KEV, and the description is based on a Coverity finding for a possible NULL dereference. The supplied sources do not provide exploitability details or a public exploit report.

Researcher notes

The evidence is sparse: no CVSS, CWE, exploit status, or distro-specific fix matrix is included. Analysis should stay close to the kernel commit and CVE text. Avoid assuming remote exploitability or impact beyond a possible NULL pointer dereference.

Mitigation direction

  • Identify Linux hosts running the affected kernel versions listed in the CVE record.
  • Review distribution or kernel-vendor advisories for fixed package versions.
  • Upgrade to a vendor-supported kernel containing the referenced stable fixes.
  • Prioritize systems using SMC networking or VLAN/lower-device configurations.

Validation and detection

  • Confirm running kernel versions against vendor advisory fixed-version data.
  • Check whether SMC networking is enabled or used in affected environments.
  • Verify patched systems include the stable commits referenced by the CVE.
  • Run normal regression testing for networking workloads after kernel updates.
Prepared
Confidence
medium
Sources
5

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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CVE-2021-47559 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
4Source 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
LinuxLinuxcb9d43f6775457cac75544bc4197f26ac2b6f294, cb9d43f6775457cac75544bc4197f26ac2b6f294, cb9d43f6775457cac75544bc4197f26ac2b6f294unaffected
LinuxLinux4.18, 0, 5.10.83, 5.15.6, 5.16affected
Weakness

CWE details

No CWE listed

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