CVE-2026-11422: Markdown Preview Enhanced 0.8.x Code Injection via WaveDrom Rendering

Synopsis

Code injection in Markdown Preview Enhanced 0.8.x (with crossnote engine below 0.9.28) allows an attacker to execute arbitrary JavaScript by embedding malicious content inside a WaveDrom fenced code block in a crafted Markdown document. The vulnerability is local and requires no authentication, but does require a victim to open the malicious file in VS Code with the extension active. Successful exploitation enables arbitrary file writes on the local filesystem by abusing the extension's message-passing channel from the VS Code webview context. Patched-image rebuilds at versions 0.8.27 and crossnote 0.9.28 are available on HarborGuard for environments running affected versions.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityNot required

  The attacker needs an existing shell or process on the host; no network-facing service is involved in the attack path.

• AuthenticationNot required

  No account or credentials are required to craft or deliver the malicious Markdown file.

• Victim interactionRequired

  The victim must open the attacker-supplied Markdown document in VS Code with the Markdown Preview Enhanced extension active, making social engineering a prerequisite.

• Attack complexityDetail

  The exploit is reliable and condition-free once the victim opens the file; no race conditions or special memory layout are needed to trigger the eval call.

Blast Radius

• Executes arbitrary JavaScript inside the VS Code webview context, giving the attacker full control over the extension's rendering sandbox.
• Writes arbitrary files to the local filesystem by abusing the extension's message-passing channel between the webview and the VS Code host process.
• Confidential files readable by the VS Code process, such as local credentials, SSH keys, or source code, can be read and exfiltrated through the injected script.