# CVE-2023-40550: Shim: out-of-bound read in verify_buffer_sbat()

> An out-of-bounds read in Shim's SBAT validation may expose sensitive data during the system boot phase on Linux operating systems.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Jan 2024
- **Updated:** 27 Jan 2026
- **Also known as:** AZL-34094, AZL-34159, AZL-35257, AZL-35265, AZL-35277, BELL-CVE-2023-40550, DEBIAN-CVE-2023-40550, GHSA-grx2-83w4-8647, UBUNTU-CVE-2023-40550

## What is CVE-2023-40550?

CVE-2023-40550 is a medium-severity vulnerability in Fedoraproject Fedora, published on 29 Jan 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An out-of-bounds read flaw was found in Shim when it tried to validate the SBAT information. This issue may expose sensitive data during the system's boot phase.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2023-40550?

It affects 3 products.


Products: Fedoraproject Fedora, Redhat Enterprise Linux, Redhat Shim.

## How do I fix CVE-2023-40550?

Apply the vendor's patch.

## Is CVE-2023-40550 being exploited?

There is no known exploitation of CVE-2023-40550 in the wild and no public exploit code.

## 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-2023-40550 and fix it if it is affected.

What it is: CVE-2023-40550 is a medium-severity vulnerability in Fedoraproject Fedora, published on 29 Jan 2024. 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-2023-40550 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-2023-40550/ (Markdown: https://insights.sbomify.com/CVE-2023-40550/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-40550
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-40550
- OSV: https://osv.dev/vulnerability/CVE-2023-40550

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-40550/
Summaries are generated and may contain mistakes; the official description above is the record.