# CVE-2026-68123: openvswitch: fix GSO userspace truncation underflow

> An integer underflow in the Linux kernel's Open vSwitch module can cause a denial of service when processing GSO packets with truncation actions.

- **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:** 10 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-68123, DEBIAN-CVE-2026-68123, GHSA-wf82-h5xg-m662, UBUNTU-CVE-2026-68123

## What is CVE-2026-68123?

CVE-2026-68123 is a critical vulnerability in Linux, published on 10 Aug 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:

openvswitch: fix GSO userspace truncation underflow

OVS_ACTION_ATTR_TRUNC currently stores a delta from the original skb
length in OVS_CB(skb)->cutlen. When a later userspace action segments a
GSO skb, queue_gso_packets() reuses that delta for each smaller segment.
A segment can then reach queue_userspace_packet() with cutlen greater
than skb->len, underflowing the length passed to skb_zerocopy().

Store the maximum preserved length instead and bound each consumer
against the current skb length. Use U32_MAX as the no-truncation
sentinel so the value remains valid if skb geometry changes before a
consumer handles it.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-68123?


## How do I fix CVE-2026-68123?

Apply the vendor's patch.

## Is CVE-2026-68123 being exploited?

There is no known exploitation of CVE-2026-68123 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68123 and fix it if it is affected.

What it is: CVE-2026-68123 is a critical vulnerability in Linux, published on 10 Aug 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-2026-68123 in the wild and no public exploit code.

Affected product: Linux. 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-2026-68123/ (Markdown: https://insights.sbomify.com/CVE-2026-68123/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68123
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68123
- OSV: https://osv.dev/vulnerability/CVE-2026-68123

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68123/
Summaries are generated and may contain mistakes; the official description above is the record.