# CVE-2021-3418: Security feature bypass in grub2

> Attackers can bypass Secure Boot signature validation to boot tampered kernels, enabling privilege escalation and code execution on affected systems.

- **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:** 15 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ALPINE-CVE-2021-3418, AZL-6467, GHSA-j6wm-c7q8-jcx7

## What is CVE-2021-3418?

CVE-2021-3418 is a medium-severity vulnerability in grub2, published on 15 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

If certificates that signed grub are installed into db, grub can be booted directly. It will then boot any kernel without signature validation. The booted kernel will think it was booted in secureboot mode and will implement lockdown, yet it could have been tampered. This flaw is a reintroduction of CVE-2020-15705 and only affects grub2 versions prior to 2.06 and upstream and distributions using the shim_lock mechanism.

Weakness: CWE-281 (Improper Preservation of Permissions)

## Which versions are affected by CVE-2021-3418?

It affects 1 product.


Products: Gnu Grub2.

## How do I fix CVE-2021-3418?

Upgrade to a fixed version.

## Is CVE-2021-3418 being exploited?

There is no known exploitation of CVE-2021-3418 in the wild and no public exploit code.

## Other vulnerabilities in grub2

- [CVE-2024-56737](https://insights.sbomify.com/CVE-2024-56737/): Memory corruption in GRUB2 (high 8.8)
- [CVE-2022-28733](https://insights.sbomify.com/CVE-2022-28733/): Integer underflow in grub_net_recv_ip4_packets (high 8.1)
- [CVE-2022-28734](https://insights.sbomify.com/CVE-2022-28734/): Out-of-bounds write when handling split HTTP headers (high 8.1)
- [CVE-2025-61662](https://insights.sbomify.com/CVE-2025-61662/): Grub2: missing unregister call for gettext command may lead to use-after-free (high 7.8)
- [CVE-2024-45782](https://insights.sbomify.com/CVE-2024-45782/): Grub2: fs/hfs: strcpy() using the volume name (fs/hfs.c:382) (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3418 and fix it if it is affected.

What it is: CVE-2021-3418 is a medium-severity vulnerability in grub2, published on 15 Mar 2021. 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-2021-3418 in the wild and no public exploit code.

Affected product: 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-2021-3418/ (Markdown: https://insights.sbomify.com/CVE-2021-3418/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3418
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3418
- OSV: https://osv.dev/vulnerability/CVE-2021-3418

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3418/
Summaries are generated and may contain mistakes; the official description above is the record.