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CVE Record

CVE-2025-21826: netfilter: nf_tables: reject mismatching sum of field_len with set key length

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: reject mismatching sum of field_len with set key length The field length description provides the length of each separated key field in the concatenation, each field gets rounded up to 32-bits to calculate the pipapo rule width from pipapo_init(). The set key length provides the total size of the key aligned to 32-bits. Register-based arithmetics still allows for combining mismatching set key length and field length description, eg. set key length 10 and field description [ 5, 4 ] leading to pipapo width of 12.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-21826 is a Linux kernel netfilter nf_tables flaw involving inconsistent rule key length validation. The sources say the kernel now rejects mismatched field lengths, but they do not state impact, CVSS severity, or exploitation. Treat it as a kernel update and exposure-management item, especially for systems relying on Linux firewalling.

Executive priority

Prioritize normal vulnerability remediation until vendor advisories assign higher severity or exploitation appears. Kernel flaws can have high operational impact, but this bundle lacks impact and exploit evidence. Focus on critical Linux firewalling infrastructure and vendor-managed appliances first.

Technical view

The issue is in nf_tables pipapo set handling. A concatenated field length description can be rounded differently from the aligned set key length, allowing inconsistent values such as key length 10 with fields 5 and 4, producing a pipapo width of 12. The fix rejects mismatched sums.

Likely exposure

Exposure is likely limited to Linux systems running affected kernel versions or vendor builds containing the vulnerable nf_tables code. The bundle lists Linux as affected and references stable kernel fixes, Debian LTS notices, and Siemens advisories. Exact product exposure depends on each distribution or appliance kernel build.

Exploitation context

The source bundle marks KEV as false and provides no evidence of active exploitation, public exploit availability, or attack prerequisites. Because the vulnerability sits in kernel firewall code, confirm exposure through kernel and vendor advisories rather than assuming every Linux host is affected.

Researcher notes

Do not infer exploitability beyond the sources. The available description identifies validation logic in nf_tables pipapo width calculation, not a complete impact statement. Research should compare affected kernel branches against the stable commits and downstream advisories, then validate whether deployed kernels contain the rejection check.

Mitigation direction

  • Apply kernel updates from Linux distribution or device vendor guidance.
  • Track Debian LTS and Siemens advisories if those platforms are in scope.
  • Prioritize firewall, gateway, container host, and appliance kernels for review.
  • Use vendor-supported kernels rather than unsupported custom builds.
  • If patching is delayed, document compensating controls and vendor guidance status.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and embedded systems.
  • Check whether running kernels include the referenced stable fixes.
  • Review distribution advisories for package names and fixed versions.
  • Confirm reboot or live-patch completion after kernel update.
  • Record systems requiring vendor firmware rather than OS package updates.
Prepared
Confidence
medium
Sources
12

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-2025-21826 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
12Source links

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

CVECVE Program Container
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux2d4c0798a1ef8db15b3277697ac2def4eda42312, 77be8c495a3f841e88b46508cc20d3d7d3289da3, 9cb084df01e198119de477ac691d682fb01e80f3, dc45bb00e66a33de1abb29e3d587880e1d4d9a7e, 3ce67e3793f48c1b9635beb9bb71116ca1e51b58, 3ce67e3793f48c1b9635beb9bb71116ca1e51b58, 3ce67e3793f48c1b9635beb9bb71116ca1e51b58, ff67e3e488090908dc015ba04d7407d8bd467f7e, 5.10.209, 5.15.148, 6.1.75, 6.6.14, 6.7.2unaffected
LinuxLinux6.8, 0, 5.10.235, 5.15.179, 6.1.129, 6.6.76, 6.12.13, 6.13.2, 6.14affected
Weakness

CWE details

No CWE listed

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