CVE-2026-46492: md-fileserver: Stored/Reflected XSS when viewing Markdown (raw HTML allowed)

Synopsis

Stored and reflected cross-site scripting (XSS) affects md-fileserver, a tool for viewing Markdown files locally in a browser. The vulnerability is reachable over the network with no authentication required and no victim interaction needed, because raw HTML embedded in Markdown content is injected into rendered pages without sanitization, allowing arbitrary JavaScript to execute in the context of the affected domain. Successful exploitation lets an attacker read sensitive page data, forge requests, or manipulate page content within the victim's browser session. HarborGuard tracks this advisory and will make a patched-image rebuild available the moment an upstream fix is published.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the md-fileserver instance over the network; the CVSS vector specifies AV:N, meaning the service is exposed to network-level access.

• AuthenticationNot required

  No credentials or account are needed; PR:N indicates the attacker can interact with the vulnerable endpoint without authenticating.

• Victim interactionNot required

  No user action such as clicking a link is needed to trigger the vulnerability; UI:N means the malicious payload executes without social engineering.

• Attack complexityDetail

  Attack complexity is low (AC:L), meaning the exploit is reliable and requires no special conditions, race timing, or environmental prerequisites.

Blast Radius

• An attacker executes arbitrary JavaScript in the browser context of the affected domain, enabling reads of cookies, session tokens, and any data visible on the rendered page.
• Injected scripts can forge authenticated requests on behalf of the current user, modifying application state or exfiltrating form inputs.
• The scope token S:C indicates the impact crosses the security boundary of the originating component, so a single compromised Markdown file can affect other resources sharing the domain.
• Confidentiality and integrity are both rated L (partial impact), meaning an attacker reads and modifies a meaningful subset of accessible data even without full control of the host.