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CVE Record

CVE-2021-47452: netfilter: nf_tables: skip netdev events generated on netns removal

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: skip netdev events generated on netns removal syzbot reported following (harmless) WARN: WARNING: CPU: 1 PID: 2648 at net/netfilter/core.c:468 nft_netdev_unregister_hooks net/netfilter/nf_tables_api.c:230 [inline] nf_tables_unregister_hook include/net/netfilter/nf_tables.h:1090 [inline] __nft_release_basechain+0x138/0x640 net/netfilter/nf_tables_api.c:9524 nft_netdev_event net/netfilter/nft_chain_filter.c:351 [inline] nf_tables_netdev_event+0x521/0x8a0 net/netfilter/nft_chain_filter.c:382 reproducer: unshare -n bash -c 'ip link add br0 type bridge; nft add table netdev t ; \ nft add chain netdev t ingress \{ type filter hook ingress device "br0" \ priority 0\; policy drop\; \}' Problem is that when netns device exit hooks create the UNREGISTER event, the .pre_exit hook for nf_tables core has already removed the base hook. Notifier attempts to do this again. The need to do base hook unregister unconditionally was needed in the past, because notifier was last stage where reg->dev dereference was safe. Now that nf_tables does the hook removal in .pre_exit, this isn't needed anymore.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysislow

Security readout for executives and security teams

Plain-English summary

This Linux kernel issue is a netfilter/nf_tables cleanup bug triggered during network namespace removal. The source describes the observed failure as a harmless kernel warning, not confirmed data theft, privilege escalation, or remote compromise. Business urgency is low unless your environment depends heavily on containers, namespaces, or nftables and runs listed affected kernels.

Executive priority

Handle through normal kernel patch management, with earlier scheduling for container infrastructure. Current public evidence does not support emergency response, but unpatched kernel bugs should not linger on shared or high-density hosts.

Technical view

nf_tables netdev notifier handling could try to unregister a base hook after nf_tables pre_exit had already removed it during network namespace teardown. syzbot reported a WARN in nf_tables/netfilter paths. The fix skips netdev events generated during netns removal. The provided sources do not include CVSS, CWE, exploitability, or impact beyond the warning.

Likely exposure

Exposure is limited to Linux systems running affected kernel versions or unpatched downstream builds with nf_tables/netdev namespace teardown behavior. Container hosts, CI runners, and systems using network namespaces are more plausible places to validate. The source bundle lists Linux 5.11, 5.14.15, and 5.15 data, but version-range detail is incomplete.

Exploitation context

No cited source reports active exploitation, and the CVE is not marked KEV. The kernel description calls the syzbot-reported WARN harmless. Treat this as a stability and hygiene issue unless vendor advisories for your distribution describe stronger impact.

Researcher notes

The source evidence is narrow: syzbot WARN, nf_tables netdev event ordering, and two stable commit references. There is no CVSS, CWE, exploit claim, or detailed affected-version matrix in the bundle, so validation should rely on distro backport status and kernel commit presence.

Mitigation direction

  • Check distribution kernel advisories for CVE-2021-47452 coverage.
  • Upgrade to a kernel containing the referenced stable fixes or vendor backports.
  • Prioritize shared container hosts and namespace-heavy systems first.
  • Avoid inventing local workarounds; follow kernel or distribution guidance.

Validation and detection

  • Inventory Linux kernel versions across servers and container hosts.
  • Confirm whether vendor changelogs include CVE-2021-47452 or the stable commits.
  • Review use of nftables netdev hooks and network namespaces.
  • Check kernel logs for related nf_tables or netfilter WARN messages.
Prepared
Confidence
medium
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

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-2021-47452 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
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

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux767d1216bff82507c945e92fe719dff2083bb2f4, 767d1216bff82507c945e92fe719dff2083bb2f4, b110391d1e806167254d3c7ae5d637191d913175, 0a0e5d47670b753d3dbf88f3c77a97a30864d9bdunaffected
LinuxLinux5.11, 0, 5.14.15, 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.