Markdown Preview Enhanced: Remote code execution via .crossnote config files
Summary
Markdown Preview Enhanced, a Visual Studio Code extension for Markdown previews, evaluates the repository-controlled files .crossnote/config.js and .crossnote/parser.js in a sandbox that is not a security boundary. An attacker who controls a repository can use prototype-chain traversal to reach the host process and run operating system commands under the victim's account. Exploitation requires only that the victim opens a Markdown file from the malicious repository.
Affected
- shd101wyy vscode-markdown-preview-enhanced before 0.8.29
Fixed in
- Version 0.8.29 or later (includes crossnote 0.9.30 with a QuickJS WebAssembly sandbox)
Workaround
Unknown. No vendor workaround has been published.
Exploitation
- CISA SSVC: exploitation status poc, automatable no, technical impact total
- Not listed in the CISA KEV catalog
- No confirmed in-the-wild exploitation known
Our recommendation
- Check endpoints, including remote development environments and devcontainers, for the extension
- Update the extension to version 0.8.29 or later
- Until the update is applied, disable the extension on systems that open untrusted repositories
- Do not open Markdown files from unknown repositories in Visual Studio Code
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- GitHub Security Advisory GHSA-427h-jhpr-8jch github.com
- Release 0.8.29 (vscode-markdown-preview-enhanced) github.com
- Fix commit (vscode-markdown-preview-enhanced) github.com
- crossnote release 0.9.30 github.com
- ProjectDiscovery write-up projectdiscovery.io
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 10:33.
Original description (NVD)
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.
NVD references (8)
- https://github.com/shd101wyy/crossnote/commit/e4890d64502e53b717cce0cb73f1a78b244dc640
- https://github.com/shd101wyy/crossnote/pull/443
- https://github.com/shd101wyy/crossnote/releases/tag/0.9.30
- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/commit/0d4010988c6ae56a38c6dec4a7509cbd5a7dcb4c
- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/pull/2320
- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/releases/tag/0.8.29
- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/security/advisories/GHSA-427h-jhpr-8jch
- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/security/advisories/GHSA-427h-jhpr-8jch
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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