# CVE-2026-23111: netfilter: nf_tables: fix inverted genmask check in nft_map_catchall_activate()

> Local attackers can exploit a use-after-free in Linux kernel nftables to achieve privilege escalation via user namespaces.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 Feb 2026
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-77483, BELL-CVE-2026-23111, DEBIAN-CVE-2026-23111, GHSA-jh9m-9mr6-3ghc, ROOT-OS-DEBIAN-11-CVE-2026-23111, ROOT-OS-DEBIAN-12-CVE-2026-23111, ROOT-OS-DEBIAN-13-CVE-2026-23111, ROOT-OS-UBUNTU-2204-CVE-2026-23111, ROOT-OS-UBUNTU-2404-CVE-2026-23111, UBUNTU-CVE-2026-23111, USN-8148-1, USN-8148-2, USN-8148-3, USN-8148-4, USN-8149-3

## What is CVE-2026-23111?

CVE-2026-23111 is a high-severity use after free vulnerability in Linux kernel, published on 13 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-672 (Operation on a Resource after Expiration or Release), CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-23111?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-23111?

Apply the vendor's patch.

## Is CVE-2026-23111 being exploited?

There is no known exploitation of CVE-2026-23111 in the wild and no public exploit code.

Public exploit code:

- CVE-2026-23111 nf_tables catchall UAF — unprivileged LPE for Linux 5.10-6.18. Auto-adaptive exploit with KASLR bypass, arbitrary kernel read, and ROP chain. Supports Debian, Ubuntu, RHEL, Fedora. C/Python/Rust + autopwn. (github_poc): https://github.com/Knz-source/CVE-2026-23111-POC-noddlenpottato
- Linux Kernel nf_tables Use-After-Free (CVE-2026-23111) — LPE PoC (github_poc): https://github.com/Baba01hacker666/CVE-2026-23111
- CVE-2026-23111 (github_poc): https://github.com/0xredash/CVE-2026-23111
- CVE-2026-23111 nf_tables UAF exploit for Ubuntu 6.8.0-101-generic: unprivileged user → host root, plus container escape to the host. (github_poc): https://github.com/kinokopio/CVE-2026-23111
- Exposure checker and safe disposable-VM lab for CVE-2026-23111 (Linux nf_tables use-after-free local privilege escalation). Defensive: detection, mitigation, multi-distro lab. No exploit. (github_poc): https://github.com/ishankaru/CVE-2026-23111-nftables-lab
- scuffed PoC for CVE-2026-23111. Made and ran on Linux Kernel 6.12.69 (github_poc): https://github.com/bakano98/cve-2026-23111-poc

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23111 and fix it if it is affected.

What it is: CVE-2026-23111 is a high-severity use after free vulnerability in Linux kernel, published on 13 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-23111 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-23111/ (Markdown: https://insights.sbomify.com/CVE-2026-23111/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23111
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23111
- OSV: https://osv.dev/vulnerability/CVE-2026-23111

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23111/
Summaries are generated and may contain mistakes; the official description above is the record.