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Response snapshot Nov 5, 2026, 00:26 UTC

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VulnerabilityCVE-2026-35571

Emissary has Stored XSS via Navigation Template Link Injection

Mustache navigation templates interpolated configuration-controlled link values directly into href attributes without URL scheme validation.

At a glance

Exploited
Not known
Severity
4.8 Medium (CVSS 3.1)
Chance of exploitation
0.2% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: gov.nsa.emissary:emissary: 8.39.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-cpm7-cfpx-3hvp (opens a new tab)

What happened

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.

Vulnerable code — nav.mustache (line 10)

{{#navItems}}
 
 {{display}} 

{{/navItems}}
Continue reading

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](https://github.com/NationalSecurityAgency/emissary/pull/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:

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:

 {{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](https://github.com/NationalSecurityAgency/emissary/pull/1293) - Original report: GHSA-wjqm-p579-x3ww

Affected package ranges reported by GitHub: gov.nsa.emissary:emissary: <= 8.38.0

Scores and how they were measured

CVSS base severity

4.8

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.2%

Scored Percentile 7.9%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-cpm7-cfpx-3hvp (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-cpm7-cfpx-3hvp, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-35571, scored 2026-11-04. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 4). Emissary has Stored XSS via Navigation Template Link Injection (CVE-2026-35571). https://kevwire.com/record/CVE-2026-35571

MLA

"Emissary has Stored XSS via Navigation Template Link Injection (CVE-2026-35571)." KEVWire, 4 Nov. 2026, kevwire.com/record/CVE-2026-35571.

Chicago

KEVWire. "Emissary has Stored XSS via Navigation Template Link Injection (CVE-2026-35571)." Last modified November 4, 2026. https://kevwire.com/record/CVE-2026-35571.

Evidence summary (plain text)

Emissary has Stored XSS via Navigation Template Link Injection (Apr 7, 2026).
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.

The {{link}} value was rendered without any scheme validation.
CVSS 4.8 (version 3.1; evidence as of Nov 4, 2026; https://github.com/advisories/GHSA-cpm7-cfpx-3hvp).
EPSS 0.2% for the following 30 days, scored Nov 4, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-35571&date=2026-11-04).
Sources:
GitHub-reviewed advisory GHSA-cpm7-cfpx-3hvp: https://github.com/advisories/GHSA-cpm7-cfpx-3hvp
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-35571&date=2026-11-04
Record ID: CVE-2026-35571.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 5, 2026, 00:26 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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