GHSA-cpm7-cfpx-3hvp Emissary has Stored XSS via Navigation Template Link Injection

• Maven gov.nsa.emissary:emissary: < 8.39.0 → fixed in 8.39.0

Summary Mustache navigation templates interpolated configuration-controlled link values directly into `href` attributes without URL scheme validation. An administrator who could modify the `navItems` configuration could inject `javascript:` URIs, enabling stored cross-site scripting (XSS) against other authenticated users viewing the Emissary web interface. Details Vulnerable code — `nav.mustache` (line 10) ```html {{#navItems}} {{display}} {{/navItems}} ``` The `{{link}}` value was rendered without any scheme validation. Mustache's default HTML escaping protects against injection of new HTML tags but does not prevent `javascript:` URIs in `href` attributes, since `javascript:` contains no characters that HTML-escaping would alter. Attack vector An administrator sets a navigation item's link to: ``` javascript:alert(document.cookie) ``` Any authenticated user who clicks the navigation link executes the script in their browser context. Impact • Session hijacking via cookie theft • Actions performed on behalf of the victim user • Requires administrative access to modify navigation configuration • Requires user interaction (clicking the malicious link) Mitigating factors • Exploitation requires administrative access to modify the `navItems` configuration • User interaction (clicking the link) is required • The Emissary web interface is typically accessed only by authenticated operators within a trusted network Remediation Fixed in PR #1293, merged into release 8.39.0. Server-side link validation — `NavAction.java` An allowlist regex was added that only permits `http://`, `https://`, or site-relative (`/`) URLs: ```java private static final Pattern VALID_LINK = Pattern.compile("^(https?:/)?/.*"); private static boolean isValidLink(String link) { if (!VALID_LINK.matcher(link).matches()) { logger.warn("Skipping invalid navigation link '{}'", link); return false; } return true; } ``` Invalid links are logged and silently dropped from the rendered navigation. Template hardening — `nav.mustache` Added `rel="noopener noreferrer"` to all navigation link anchor tags as a defense-in-depth measure: ```html {{display}} ``` Tests were added to verify that `javascript:` and `ftp://` URIs are rejected while `http://`, `https://`, and site-relative (`/path`) links are accepted. Workarounds If upgrading is not immediately possible, audit the navigation configuration to ensure all `navItems` link values use only `http://`, `https://`, or relative (`/`) URL schemes. References • PR #1293 — validate nav links • Original report: GHSA-wjqm-p579-x3ww