# CVE-2026-97876: Bypass of GRUB lockdown restriction in Secure Boot mode via serial command MMIO base address

> A local attacker can bypass Secure Boot lockdown restrictions in GRUB to load unsigned modules by exploiting insufficient MMIO address validation.

- **Severity:** Medium 6.4 (`CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 2 Oct 2026
- **Updated:** 2 Oct 2026
- **Also known as:** BELL-CVE-2026-97876, DEBIAN-CVE-2026-97876, GHSA-v555-hf4g-q6pc, UBUNTU-CVE-2026-97876

## What is CVE-2026-97876?

CVE-2026-97876 is a medium-severity vulnerability in GNU grub2, published on 2 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A local attacker with control over GRUB's configuration can bypass lockdown restrictions when booting with Secure Boot and load an unsigned GRUB module, while GRUB continues to report lockdown is enabled.

The vulnerability is caused by insufficient validation of the MMIO base address passed to the GRUB serial command. GRUB does not validate that the base address corresponds to a UART device, rather than being an arbitrary memory address. This allows an attacker to trick GRUB into writing non-arbitrary data at an attacker-controlled address, including resetting the grub_file_verifiers list in a way that disables the subsequent verification of loaded modules.

Weakness: CWE-822 (Untrusted Pointer Dereference)

## Which versions are affected by CVE-2026-97876?


## How do I fix CVE-2026-97876?

Apply the vendor's patch.

## Is CVE-2026-97876 being exploited?

There is no known exploitation of CVE-2026-97876 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97876 and fix it if it is affected.

What it is: CVE-2026-97876 is a medium-severity vulnerability in GNU grub2, published on 2 Oct 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-2026-97876 in the wild and no public exploit code.

Affected product: GNU grub2. 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-2026-97876/ (Markdown: https://insights.sbomify.com/CVE-2026-97876/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97876
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97876
- OSV: https://osv.dev/vulnerability/CVE-2026-97876

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97876/
Summaries are generated and may contain mistakes; the official description above is the record.