# CVE-2026-68299: vmxnet3: fix BUG_ON in vmxnet3_get_hdr_len() for Geneve packets

> A remote attacker can crash the Linux kernel by sending specially crafted Geneve packets to a system using the vmxnet3 driver.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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-2026-68299, DEBIAN-CVE-2026-68299, GHSA-m243-8cm2-374c, UBUNTU-CVE-2026-68299

## What is CVE-2026-68299?

CVE-2026-68299 is a high-severity denial of service 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:

vmxnet3: fix BUG_ON in vmxnet3_get_hdr_len() for Geneve packets

vmxnet3_get_hdr_len() assumes gdesc->rcd.v4/v6/tcp always describe the
outer header, but for a Geneve-encapsulated packet the device can set
them based on the inner header instead, signalled by the
VMXNET3_RCD_HDR_INNER_SHIFT bit in the completion descriptor. Since the
function never skips the outer encapsulation, this mismatch triggers:

- BUG_ON(hdr.ipv4->protocol != IPPROTO_TCP), because the outer
  protocol is UDP (Geneve), not TCP.
- BUG_ON(hdr.eth->h_proto != ...), when the tunnel's outer and inner
  IP versions differ (e.g. outer IPv6/inner IPv4 or vice versa).

Check VMXNET3_RCD_HDR_INNER_SHIFT up front and bail out, since the
function cannot locate the inner header it would need to parse. Also
convert the remaining BUG_ON()s in this function to return 0
defensively.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-68299?


## How do I fix CVE-2026-68299?

Apply the vendor's patch.

## Is CVE-2026-68299 being exploited?

There is no known exploitation of CVE-2026-68299 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68299 and fix it if it is affected.

What it is: CVE-2026-68299 is a high-severity denial of service 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-2026-68299 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-2026-68299/ (Markdown: https://insights.sbomify.com/CVE-2026-68299/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68299
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68299
- OSV: https://osv.dev/vulnerability/CVE-2026-68299

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68299/
Summaries are generated and may contain mistakes; the official description above is the record.