Security readout for executives and security teams
Plain-English summary
This Linux kernel flaw affects netfilter connection tracking logic. A crafted or unusual nftables connection-tracking expectation path can trigger incorrect handling of already confirmed connections. The published severity is medium, with limited confidentiality and integrity impact and no availability impact in the supplied CVSS data.
Executive priority
Treat this as a routine but necessary Linux kernel maintenance item. It is not documented as actively exploited in the supplied evidence, but affected network security infrastructure should be patched promptly because it sits on sensitive traffic paths.
Technical view
nft_ct_expect_obj_eval() could call nf_ct_ext_add() on a confirmed conntrack entry, although that extension add path is only valid before confirmation. The kernel fix skips confirmed and template conntrack entries, and limits expectation creation to the first packet unless future helper attachment logic changes.
Likely exposure
Exposure is most relevant on Linux systems using nftables/netfilter connection tracking expectations, especially firewall, routing, gateway, container host, or network appliance workloads. The bundle identifies Linux kernel versions and stable fixes, but distro backport status must be checked separately.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation. CVSS indicates network reachability, low attack complexity, low privileges, and required user interaction. No public exploit evidence is provided in the supplied sources.
Researcher notes
The key behavioral change is avoiding helper extension attachment after conntrack confirmation and skipping template conntrack. The source evidence is kernel-focused and does not provide exploit proof, affected distribution matrices, or operational mitigations beyond applying fixed kernel code.
Mitigation direction
- Update to a vendor-supported kernel containing the listed upstream stable fixes.
- Check Linux distribution advisories for backported fixes before relying on version numbers alone.
- Prioritize internet-facing firewalls, routers, gateways, and hosts using nftables conntrack expectations.
- If updating is delayed, follow vendor guidance for netfilter or nftables exposure reduction.
Validation and detection
- Inventory running kernel versions across Linux hosts and network appliances.
- Identify systems using nftables, nf_tables, nft_ct, or conntrack expectation features.
- Verify package changelogs reference the upstream fix or CVE-2021-47129.
- Review firewall and gateway assets first, then lower-exposure servers.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-273: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-47129 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 4.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
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.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N2.12.5CISA-ADPVulnerability scoring details
Base CVSS 3.1 score
4.6MediumVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://git.kernel.org/stable/c/da8d31e80ff425f5a65dab7060d5c4aba749e562CVE reference, Linux
- https://git.kernel.org/stable/c/5f3429c05e4028a0e241afdad856dd15dec2ffb9CVE reference, Linux
- https://git.kernel.org/stable/c/2c0e6b35b88a961127066a1028bce9c727cbc3e5CVE reference, Linux
- https://git.kernel.org/stable/c/1710eb913bdcda3917f44d383c32de6bdabfc836CVE reference, Linux
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Check for Dropped Privileges
Improper Check for Dropped Privileges represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.