# CVE-2026-63868: net: garp: fix unsigned integer underflow in garp_pdu_parse_attr

> An integer underflow in the Linux kernel GARP parser causes received Join/Leave events to be ignored, breaking VLAN registration and causing denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 19 Jul 2026
- **Also known as:** BELL-CVE-2026-63868, DEBIAN-CVE-2026-63868, GHSA-3pm7-r452-gg96, ROOT-OS-UBUNTU-2204-CVE-2026-63868, UBUNTU-CVE-2026-63868

## What is CVE-2026-63868?

CVE-2026-63868 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 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: garp: fix unsigned integer underflow in garp_pdu_parse_attr

The receive-side GARP attribute parser computes dlen with reversed
operands:

        dlen = sizeof(*ga) - ga->len;

ga->len is the on-wire attribute length and includes the GARP attribute
header. For normal attributes with data, ga->len is larger than
sizeof(*ga), so the subtraction underflows in unsigned arithmetic.

The resulting value is later passed to garp_attr_lookup(), whose length
argument is u8. After truncation, the parsed data length usually no
longer matches the length stored for locally registered attributes, so
received Join/Leave events are ignored. This breaks the GARP receive path
for common attributes, such as GVRP VLAN registration attributes.

Compute the data length as the attribute length minus the header length.

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

## Which versions are affected by CVE-2026-63868?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-63868?

Apply the vendor's patch.

## Is CVE-2026-63868 being exploited?

There is no known exploitation of CVE-2026-63868 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-2026-63868 and fix it if it is affected.

What it is: CVE-2026-63868 is a medium-severity vulnerability in Linux kernel, published on 19 Jul 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-2026-63868 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-2026-63868/ (Markdown: https://insights.sbomify.com/CVE-2026-63868/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63868
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63868
- OSV: https://osv.dev/vulnerability/CVE-2026-63868

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63868/
Summaries are generated and may contain mistakes; the official description above is the record.