# CVE-2021-20233: Memory corruption in grub2

> An attacker can corrupt memory in GRUB2 via crafted input, potentially leading to code execution or privilege escalation during boot.

- **Severity:** High 8.2 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/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:** 3 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ALPINE-CVE-2021-20233, AZL-6466, AZL-78305, DEBIAN-CVE-2021-20233, GHSA-257g-8w4g-3cc3, UBUNTU-CVE-2021-20233

## What is CVE-2021-20233?

CVE-2021-20233 is a high-severity memory corruption vulnerability in Fedoraproject Fedora, published on 3 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw was found in grub2 in versions prior to 2.06. Setparam_prefix() in the menu rendering code performs a length calculation on the assumption that expressing a quoted single quote will require 3 characters, while it actually requires 4 characters which allows an attacker to corrupt memory by one byte for each quote in the input. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2021-20233?

It affects 8 products.


Products: Fedoraproject Fedora, Gnu Grub2, Netapp Ontap Select Deploy Administration Utility, Redhat Enterprise Linux, Redhat Enterprise Linux Server Aus, Redhat Enterprise Linux Server Eus, Redhat Enterprise Linux Server Tus, Redhat Enterprise Linux Workstation.

## How do I fix CVE-2021-20233?

Upgrade to a fixed version.

## Is CVE-2021-20233 being exploited?

There is no known exploitation of CVE-2021-20233 in the wild and no public exploit code.

Public exploit code:

- This script will remediate the BootHole bug identified in CVE-2020-25632 and/or CVE-2021-20233. (github_poc): https://github.com/pauljrowland/BootHoleFix

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20233 and fix it if it is affected.

What it is: CVE-2021-20233 is a high-severity memory corruption vulnerability in Fedoraproject Fedora, published on 3 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-2021-20233 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2021-20233/ (Markdown: https://insights.sbomify.com/CVE-2021-20233/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20233
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20233
- OSV: https://osv.dev/vulnerability/CVE-2021-20233

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20233/
Summaries are generated and may contain mistakes; the official description above is the record.