# CVE-2009-4128: Auth bypass in n/a

> Physically proximate attackers can bypass GRUB password authentication by submitting a single-character password, allowing unauthorized system access.

- **Severity:** High 7.2 (`AV:L/AC:L/Au:N/C:C/I:C/A:C`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 1 Dec 2009
- **Updated:** 7 Aug 2024
- **Also known as:** DEBIAN-CVE-2009-4128, GHSA-prgr-9xf7-v9fw

## What is CVE-2009-4128?

CVE-2009-4128 is a high-severity authentication bypass vulnerability in n/a, published on 1 Dec 2009. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

GNU GRand Unified Bootloader (GRUB) 2 1.97 only compares the submitted portion of a password with the actual password, which makes it easier for physically proximate attackers to conduct brute force attacks and bypass authentication by submitting a password whose length is 1.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2009-4128?

It affects 1 product.


Products: Gnu Grub 2.

## How do I fix CVE-2009-4128?

Apply the vendor's patch.

## Is CVE-2009-4128 being exploited?

There is no known exploitation of CVE-2009-4128 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2009-4128 and fix it if it is affected.

What it is: CVE-2009-4128 is a high-severity authentication bypass vulnerability in n/a, published on 1 Dec 2009. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2009-4128 in the wild and no public exploit code.

Affected product: n/a. 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-2009-4128/ (Markdown: https://insights.sbomify.com/CVE-2009-4128/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2009-4128
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2009-4128
- OSV: https://osv.dev/vulnerability/CVE-2009-4128

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From sbomify Insights: https://insights.sbomify.com/CVE-2009-4128/
Summaries are generated and may contain mistakes; the official description above is the record.