# CVE-2026-54566: Markdown Preview Enhanced code execution via untrusted config.js

Source: https://junglewise.ai/threats/cve-2026-54566-markdown-preview-enhanced-is-a-markdown-preview-extension-for  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-14. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-54566 · Severity: info · Published 2026-10-14

Markdown Preview Enhanced is a preview extension for Visual Studio Code that renders Markdown files. When opening a Markdown file from a malicious repository, the extension automatically loads and executes repository-controlled configuration and parser files without proper security isolation, allowing an attacker to run arbitrary operating-system commands with the victim's privileges without any user interaction beyond opening the file.

Technologies: [Shd101wyy Markdown Preview Enhanced](https://junglewise.ai/threats/technologies/markdown-preview-enhanced). Vendors: [Shd101wyy](https://junglewise.ai/threats/vendors/shd101wyy).

## Quick answers

**Is CVE-2026-54566 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-54566 being exploited in the wild.

**How severe is CVE-2026-54566?** Informational severity, published 14 October 2026.

**Which products and versions are affected?** Shd101wyy Markdown Preview Enhanced before 0.8.29.

**Is there a fix for CVE-2026-54566?** Yes: fixed in 0.8.29. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-54566 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-54566?** Check whether you run Shd101wyy Markdown Preview Enhanced at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 0.8.29

## Technical details

The vulnerability exists in the evaluation of .crossnote/config.js and .crossnote/parser.js files using vm.runInNewContext() and sval, neither of which provides a security boundary from the Node.js host realm. Attackers can use prototype-chain traversal via ({}).constructor.constructor to reach the host Function constructor and access the process object, achieving remote code execution simply by a user opening a Markdown file in a malicious repository. The fix isolates these files in a QuickJS WebAssembly sandbox with separate realm and intrinsics, preventing access to host globals and process.

## Affected products

- shd101wyy Markdown Preview Enhanced before 0.8.29

## Timeline

- 2026-10-14: disclosed
- 2026-06-06: patched: Fix released in version 0.9.30 with QuickJS WebAssembly sandbox

## References

- [https://github.com/shd101wyy/crossnote/commit/e4890d64502e53b717cce0cb73f1a78b244dc640](https://github.com/shd101wyy/crossnote/commit/e4890d64502e53b717cce0cb73f1a78b244dc640)
- [https://github.com/shd101wyy/crossnote/pull/443](https://github.com/shd101wyy/crossnote/pull/443)

## Related threats

- [Markdown Preview Enhanced command injection in webview message handler](https://junglewise.ai/threats/cve-2026-54702-markdown-preview-enhanced-is-a-markdown-preview-extension-for)
- [Markdown Preview Enhanced command injection in preview links on Windows](https://junglewise.ai/threats/cve-2026-54525-markdown-preview-enhanced-is-a-markdown-preview-extension-for)
- [Markdown Preview Enhanced code injection in WaveDrom rendering](https://junglewise.ai/threats/cve-2026-11422-markdown-preview-enhanced-code-injection-in-wavedrom-rendering)
- [Markdown Preview Enhanced code injection in WaveDrom rendering](https://junglewise.ai/threats/cve-2026-50733-markdown-preview-enhanced-code-injection-in-wavedrom-rendering)
- [Markdown Preview Enhanced code execution in Bitfield renderer](https://junglewise.ai/threats/cve-2026-49493-markdown-preview-enhanced-code-execution-in-bitfield-renderer)