CVE-2026-35571

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)

{{#navItems}}
<li class="nav-item">
  <a class="nav-link" href="{{link}}">{{display}}</a>
</li>
{{/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.

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

Server-side link validation, NavAction.java

An allowlist regex was added that only permits http://, https://, or
site-relative (/) URLs:

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:

<a class="nav-link" href="{{link}}" rel="noopener noreferrer">{{display}}</a>

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

• 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)

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-35571 has a CVSS score of 4.8 (Medium). The vector is network-reachable, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (8.39.0); upgrading removes the vulnerable code path.

Kodem intelligence

Fixed in PR #1293,
merged into release 8.39.0.

1. What is CVE-2026-35571? CVE-2026-35571 is a medium-severity cross-site scripting (XSS) vulnerability in gov.nsa.emissary:emissary (maven), affecting versions <= 8.38.0. It is fixed in 8.39.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-35571? CVE-2026-35571 has a CVSS score of 4.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of gov.nsa.emissary:emissary are affected by CVE-2026-35571? gov.nsa.emissary:emissary (maven) versions <= 8.38.0 is affected.
4. Is there a fix for CVE-2026-35571? Yes. CVE-2026-35571 is fixed in 8.39.0. Upgrade to this version or later.
5. Is CVE-2026-35571 exploitable, and should I be worried? Whether CVE-2026-35571 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-35571 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-35571? Upgrade gov.nsa.emissary:emissary to 8.39.0 or later.