# CVE-2026-31680: net: ipv6: flowlabel: defer exclusive option free until RCU teardown

> A race condition in the Linux kernel IPv6 flowlabel handling allows a local attacker to trigger a use-after-free crash via concurrent access to proc files.

- **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:** 25 Apr 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-84213, BELL-CVE-2026-31680, DEBIAN-CVE-2026-31680, GHSA-2xwr-gh6x-hm86, ROOT-OS-DEBIAN-11-CVE-2026-31680, ROOT-OS-DEBIAN-12-CVE-2026-31680, ROOT-OS-UBUNTU-2204-CVE-2026-31680, ROOT-OS-UBUNTU-2404-CVE-2026-31680, UBUNTU-CVE-2026-31680

## What is CVE-2026-31680?

CVE-2026-31680 is a high-severity use after free vulnerability in Linux kernel, published on 25 Apr 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:

net: ipv6: flowlabel: defer exclusive option free until RCU teardown

`ip6fl_seq_show()` walks the global flowlabel hash under the seq-file
RCU read-side lock and prints `fl->opt->opt_nflen` when an option block
is present.

Exclusive flowlabels currently free `fl->opt` as soon as `fl->users`
drops to zero in `fl_release()`. However, the surrounding
`struct ip6_flowlabel` remains visible in the global hash table until
later garbage collection removes it and `fl_free_rcu()` finally tears it
down.

A concurrent `/proc/net/ip6_flowlabel` reader can therefore race that
early `kfree()` and dereference freed option state, triggering a crash
in `ip6fl_seq_show()`.

Fix this by keeping `fl->opt` alive until `fl_free_rcu()`. That matches
the lifetime already required for the enclosing flowlabel while readers
can still reach it under RCU.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-31680?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31680?

Apply the vendor's patch.

## Is CVE-2026-31680 being exploited?

There is no known exploitation of CVE-2026-31680 in the wild and no public exploit code.

## 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-2026-31680 and fix it if it is affected.

What it is: CVE-2026-31680 is a high-severity use after free vulnerability in Linux kernel, published on 25 Apr 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-2026-31680 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-2026-31680/ (Markdown: https://insights.sbomify.com/CVE-2026-31680/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31680
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31680
- OSV: https://osv.dev/vulnerability/CVE-2026-31680

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31680/
Summaries are generated and may contain mistakes; the official description above is the record.