# CVE-2026-31668: seg6: separate dst_cache for input and output paths in seg6 lwtunnel

> A race condition in Linux kernel seg6 lwtunnel allows routing cache poisoning, potentially bypassing routing policies or leaking data.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Apr 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-83813, BELL-CVE-2026-31668, DEBIAN-CVE-2026-31668, GHSA-r2p4-96h8-cc74, ROOT-OS-DEBIAN-11-CVE-2026-31668, ROOT-OS-DEBIAN-12-CVE-2026-31668, ROOT-OS-DEBIAN-13-CVE-2026-31668, ROOT-OS-UBUNTU-2204-CVE-2026-31668, ROOT-OS-UBUNTU-2404-CVE-2026-31668, UBUNTU-CVE-2026-31668

## What is CVE-2026-31668?

CVE-2026-31668 is a critical vulnerability in Linux kernel, published on 24 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

seg6: separate dst_cache for input and output paths in seg6 lwtunnel

The seg6 lwtunnel uses a single dst_cache per encap route, shared
between seg6_input_core() and seg6_output_core(). These two paths
can perform the post-encap SID lookup in different routing contexts
(e.g., ip rules matching on the ingress interface, or VRF table
separation). Whichever path runs first populates the cache, and the
other reuses it blindly, bypassing its own lookup.

Fix this by splitting the cache into cache_input and cache_output,
so each path maintains its own cached dst independently.

Weakness: CWE-459 (Incomplete Cleanup)

## Which versions are affected by CVE-2026-31668?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31668?

Apply the vendor's patch.

## Is CVE-2026-31668 being exploited?

There is no known exploitation of CVE-2026-31668 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-2026-31668 and fix it if it is affected.

What it is: CVE-2026-31668 is a critical vulnerability in Linux kernel, published on 24 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31668 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-2026-31668/ (Markdown: https://insights.sbomify.com/CVE-2026-31668/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31668
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31668
- OSV: https://osv.dev/vulnerability/CVE-2026-31668

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31668/
Summaries are generated and may contain mistakes; the official description above is the record.