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CVE Record

CVE-2021-46913: netfilter: nftables: clone set element expression template

In the Linux kernel, the following vulnerability has been resolved: netfilter: nftables: clone set element expression template memcpy() breaks when using connlimit in set elements. Use nft_expr_clone() to initialize the connlimit expression list, otherwise connlimit garbage collector crashes when walking on the list head copy. [ 493.064656] Workqueue: events_power_efficient nft_rhash_gc [nf_tables] [ 493.064685] RIP: 0010:find_or_evict+0x5a/0x90 [nf_conncount] [ 493.064694] Code: 2b 43 40 83 f8 01 77 0d 48 c7 c0 f5 ff ff ff 44 39 63 3c 75 df 83 6d 18 01 48 8b 43 08 48 89 de 48 8b 13 48 8b 3d ee 2f 00 00 <48> 89 42 08 48 89 10 48 b8 00 01 00 00 00 00 ad de 48 89 03 48 83 [ 493.064699] RSP: 0018:ffffc90000417dc0 EFLAGS: 00010297 [ 493.064704] RAX: 0000000000000000 RBX: ffff888134f38410 RCX: 0000000000000000 [ 493.064708] RDX: 0000000000000000 RSI: ffff888134f38410 RDI: ffff888100060cc0 [ 493.064711] RBP: ffff88812ce594a8 R08: ffff888134f38438 R09: 00000000ebb9025c [ 493.064714] R10: ffffffff8219f838 R11: 0000000000000017 R12: 0000000000000001 [ 493.064718] R13: ffffffff82146740 R14: ffff888134f38410 R15: 0000000000000000 [ 493.064721] FS: 0000000000000000(0000) GS:ffff88840e440000(0000) knlGS:0000000000000000 [ 493.064725] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 493.064729] CR2: 0000000000000008 CR3: 00000001330aa002 CR4: 00000000001706e0 [ 493.064733] Call Trace: [ 493.064737] nf_conncount_gc_list+0x8f/0x150 [nf_conncount] [ 493.064746] nft_rhash_gc+0x106/0x390 [nf_tables]

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-46913 is a Linux kernel nftables bug that can crash kernel networking garbage collection when certain connlimit expressions are used in set elements. The public bundle does not provide CVSS, confirmed exploitation, or a broad product matrix, so urgency depends on whether affected Linux kernels and nftables configurations are present.

Executive priority

Treat this as a targeted kernel availability issue rather than a broad emergency. Prioritize patch validation for firewalls, gateways, container hosts, and other Linux systems where nftables failure could disrupt services or security controls.

Technical view

The flaw is in netfilter nftables set element expression handling. A memcpy-based clone of a connlimit expression template copied list-head state incorrectly; nft_expr_clone() is required. The documented failure path crashes nf_conncount garbage collection during nft_rhash_gc, indicating a kernel stability and availability risk in specific rule configurations.

Likely exposure

Exposure appears limited to Linux systems running affected kernel versions with nftables/nf_tables rules that use connlimit expressions in set elements. The source bundle lists affected Linux kernel versions including 5.7, 5.10.64, 5.11.16, and 5.12, but distro backport status is not provided.

Exploitation context

The bundle does not cite active exploitation, and KEV is false. Evidence supports a crash condition in kernel garbage collection, not remote code execution. Practical exploitability depends on local rule-management capability or deployed rules that exercise the vulnerable nftables connlimit path.

Researcher notes

The source bundle gives a precise root cause and crash stack but lacks CVSS, CWE, exploit reports, and distro-specific fixed versions. Avoid overstating impact beyond kernel crash risk tied to nftables connlimit set elements unless additional vendor advisories confirm broader exposure.

Mitigation direction

  • Update to a vendor-supported Linux kernel containing the referenced stable fixes.
  • Check Linux distribution advisories for backported fixes for CVE-2021-46913.
  • Limit nftables rule administration to trusted privileged operators.
  • Review nftables rules using connlimit expressions in set elements.
  • Prioritize systems where firewall availability is operationally critical.

Validation and detection

  • Inventory Linux kernel versions across exposed hosts and appliances.
  • Confirm whether nf_tables/nftables is enabled and actively used.
  • Review rulesets for connlimit expressions inside set elements.
  • Check vendor kernel changelogs for the referenced stable commits.
  • Review kernel logs for nf_conncount or nft_rhash_gc crash traces.
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-2021-46913 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
LinuxLinux4094445229760d0d31a4190dfe88fe815c9fc34e, 4094445229760d0d31a4190dfe88fe815c9fc34e, 4094445229760d0d31a4190dfe88fe815c9fc34eunaffected
LinuxLinux5.7, 0, 5.10.64, 5.11.16, 5.12affected
Weakness

CWE details

No CWE listed

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