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CVE Record

CVE-2021-47495: usbnet: sanity check for maxpacket

In the Linux kernel, the following vulnerability has been resolved: usbnet: sanity check for maxpacket maxpacket of 0 makes no sense and oopses as we need to divide by it. Give up. V2: fixed typo in log and stylistic issues

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-47495 is a Linux kernel usbnet flaw where an invalid zero packet size can crash the kernel path that divides by that value. Business impact is most likely denial of service on systems that use USB network devices. The source bundle does not show data theft, privilege escalation, or confirmed exploitation.

Executive priority

Schedule remediation through normal kernel patching, with higher priority for systems where untrusted people can connect USB devices or where a crash affects safety, operations, or availability.

Technical view

The Linux kernel usbnet driver lacked a sanity check for maxpacket. A maxpacket value of 0 caused an oops because the code divided by it. Upstream stable commits add validation and give up when maxpacket is invalid. Affected kernel ranges are listed across long-term stable branches through 5.15-era releases.

Likely exposure

Exposure is most plausible on Linux endpoints, embedded systems, appliances, or servers where USB network interfaces are supported and an invalid USB network device can be attached or presented.

Exploitation context

The bundle marks KEV false and provides no cited evidence of active exploitation. It also provides no public exploit details. Treat this as a reliability and local or physical-adjacent denial-of-service risk unless vendor guidance says otherwise.

Researcher notes

Evidence supports an input-validation bug in usbnet causing kernel oops through divide-by-zero behavior. The bundle does not include CVSS, CWE, exploitability analysis, or distribution-specific fixed package versions, so validation should rely on vendor backport confirmation.

Mitigation direction

  • Apply Linux kernel updates containing the referenced upstream stable fixes.
  • Check your Linux distribution vendor advisory for backported fixes.
  • Restrict untrusted USB device attachment on sensitive systems.
  • Disable unused usbnet-related drivers where operationally safe.
  • Prioritize embedded or kiosk systems exposed to physical USB access.

Validation and detection

  • Inventory Linux kernel versions across endpoints, appliances, and embedded devices.
  • Confirm vendor kernel builds include a CVE-2021-47495 backport.
  • Identify systems with usbnet modules available or loaded.
  • Review device-control policy for untrusted USB network adapters.
  • Monitor kernel logs for usbnet-related oops or crash reports.
Prepared
Confidence
medium
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

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CVE-2021-47495 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
9Source 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
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2unaffected
LinuxLinux2.6.12, 0, 4.4.291, 4.9.289, 4.14.254, 4.19.215, 5.4.157, 5.10.77, 5.14.16, 5.15affected
Weakness

CWE details

No CWE listed

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