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CVE Record

CVE-2021-47013: net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send

In the Linux kernel, the following vulnerability has been resolved: net:emac/emac-mac: Fix a use after free in emac_mac_tx_buf_send In emac_mac_tx_buf_send, it calls emac_tx_fill_tpd(..,skb,..). If some error happens in emac_tx_fill_tpd(), the skb will be freed via dev_kfree_skb(skb) in error branch of emac_tx_fill_tpd(). But the freed skb is still used via skb->len by netdev_sent_queue(,skb->len). As i observed that emac_tx_fill_tpd() haven't modified the value of skb->len, thus my patch assigns skb->len to 'len' before the possible free and use 'len' instead of skb->len later.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2021-47013 is a Linux kernel memory-safety bug in the EMAC network driver transmit path. A packet buffer can be freed during error handling and then referenced afterward. The public record does not provide a severity score, impact statement, or evidence of active exploitation.

Executive priority

Treat this as a targeted kernel maintenance item, not an emergency based on current evidence. Prioritize affected embedded or network-facing Linux systems using the EMAC driver, and fold fixes into the next validated kernel update cycle unless vendor guidance raises severity.

Technical view

The flaw is a use-after-free in emac_mac_tx_buf_send. emac_tx_fill_tpd may free skb on an error path, but the caller later reads skb->len for netdev_sent_queue. Stable kernel commits fix this by saving the length before the possible free and using that saved value afterward.

Likely exposure

Exposure appears limited to systems running affected Linux kernel versions with the EMAC network driver code present and relevant hardware or configuration. The source lists affected Linux versions including 4.9, 4.14.233, 4.19.191, 5.4.119, 5.10.37, 5.11.21, 5.12.4, and 5.13.

Exploitation context

The provided sources do not show active exploitation, public exploit availability, or KEV listing. The likely security concern is kernel memory corruption or crash potential in an affected driver path, but the record does not prove practical exploitability or remote reachability.

Researcher notes

The record lacks CVSS, CWE, exploit status, and detailed impact. Analysis should stay anchored to the driver-specific use-after-free and the stable commit behavior. Avoid broad claims that all Linux systems are practically exposed.

Mitigation direction

  • Apply distribution kernel updates that include the referenced Linux stable fixes.
  • Check vendor kernel advisories for affected packages and fixed release versions.
  • Prioritize systems using EMAC network hardware or related embedded Linux builds.
  • If patching is delayed, assess whether the EMAC driver is needed in production.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and embedded systems.
  • Confirm whether EMAC driver support is enabled or loaded on each system.
  • Map installed kernels against vendor advisories and the referenced stable commits.
  • Verify patched kernels are booted, not only installed.
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.

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CVE-2021-47013 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
LinuxLinuxb9b17debc69d27cd55e21ee51a5ba7fc50a426cf, b9b17debc69d27cd55e21ee51a5ba7fc50a426cf, b9b17debc69d27cd55e21ee51a5ba7fc50a426cf, b9b17debc69d27cd55e21ee51a5ba7fc50a426cf, b9b17debc69d27cd55e21ee51a5ba7fc50a426cf, b9b17debc69d27cd55e21ee51a5ba7fc50a426cf, b9b17debc69d27cd55e21ee51a5ba7fc50a426cf, b9b17debc69d27cd55e21ee51a5ba7fc50a426cfunaffected
LinuxLinux4.9, 0, 4.9.269, 4.14.233, 4.19.191, 5.4.119, 5.10.37, 5.11.21, 5.12.4, 5.13affected
Weakness

CWE details

No CWE listed

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