# CVE-2026-54566: Code injection in vscode-markdown-preview-enhanced

> Attackers can execute arbitrary OS commands by tricking users into opening a malicious repository, exploiting unsafe JavaScript evaluation in the Markdown Preview Enhanced extension.

- **Severity:** High 8.5 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **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:** No
- **Published:** 14 Oct 2026
- **Updated:** 14 Oct 2026
- **Also known as:** GHSA-427h-jhpr-8jch

## What is CVE-2026-54566?

CVE-2026-54566 is a high-severity code injection vulnerability in shd101wyy vscode-markdown-preview-enhanced, published on 14 Oct 2026. 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

Markdown Preview Enhanced is a Markdown preview extension for Visual Studio Code. Prior to 0.8.29, Markdown Preview Enhanced evaluates repository-controlled .crossnote/config.js and .crossnote/parser.js files with vm.runInNewContext, which does not provide a security boundary from the Node.js host realm. Opening a Markdown file in a malicious repository automatically loads these files, and prototype-chain traversal can reach the host Function constructor and process object, allowing operating-system commands to execute as the victim account without further interaction. Both configuration evaluation and parser-hook evaluation are affected, and the attack does not depend on module-scoped require being available. This issue is fixed in version 0.8.29.

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-54566?


## How do I fix CVE-2026-54566?

No fix has been published for CVE-2026-54566 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-54566 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54566 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54566 and fix it if it is affected.

What it is: CVE-2026-54566 is a high-severity code injection vulnerability in shd101wyy vscode-markdown-preview-enhanced, published on 14 Oct 2026. 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54566 exists.

Affected product: shd101wyy vscode-markdown-preview-enhanced. 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-2026-54566/ (Markdown: https://insights.sbomify.com/CVE-2026-54566/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54566
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54566
- OSV: https://osv.dev/vulnerability/CVE-2026-54566

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-54566/
Summaries are generated and may contain mistakes; the official description above is the record.