CVE-2026-35571: Emissary Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-cpm7-cfpx-3hvp",
  "modified" : "2026-04-07T20:17:14Z",
  "published" : "2026-04-07T20:17:14Z",
  "aliases" : [ "CVE-2026-35571" ],
  "summary" : "Emissary has Stored XSS via Navigation Template Link Injection",
  "details" : "## Summary\n\nMustache navigation templates interpolated configuration-controlled link values\ndirectly into `href` attributes without URL scheme validation. An administrator\nwho could modify the `navItems` configuration could inject `javascript:` URIs,\nenabling stored cross-site scripting (XSS) against other authenticated users\nviewing the Emissary web interface.\n\n## Details\n\n### Vulnerable code — `nav.mustache` (line 10)\n\n```html\n{{#navItems}}\n<li class=\"nav-item\">\n  <a class=\"nav-link\" href=\"{{link}}\">{{display}}</a>\n</li>\n{{/navItems}}\n```\n\nThe `{{link}}` value was rendered without any scheme validation. Mustache's\ndefault HTML escaping protects against injection of new HTML tags but does\n**not** prevent `javascript:` URIs in `href` attributes, since `javascript:`\ncontains no characters that HTML-escaping would alter.\n\n### Attack vector\n\nAn administrator sets a navigation item's link to:\n```\njavascript:alert(document.cookie)\n```\n\nAny authenticated user who clicks the navigation link executes the script in\ntheir browser context.\n\n### Impact\n\n- Session hijacking via cookie theft\n- Actions performed on behalf of the victim user\n- Requires administrative access to modify navigation configuration\n- Requires user interaction (clicking the malicious link)\n\n### Mitigating factors\n\n- Exploitation requires administrative access to modify the `navItems`\n  configuration\n- User interaction (clicking the link) is required\n- The Emissary web interface is typically accessed only by authenticated\n  operators within a trusted network\n\n## Remediation\n\nFixed in [PR #1293](https://github.com/NationalSecurityAgency/emissary/pull/1293),\nmerged into release 8.39.0.\n\n### Server-side link validation — `NavAction.java`\n\nAn allowlist regex was added that only permits `http://`, `https://`, or\nsite-relative (`/`) URLs:\n\n```java\nprivate static final Pattern VALID_LINK = Pattern.compile(\"^(https?:/)?/.*\");\n\nprivate static boolean isValidLink(String link) {\n    if (!VALID_LINK.matcher(link).matches()) {\n        logger.warn(\"Skipping invalid navigation link '{}'\", link);\n        return false;\n    }\n    return true;\n}\n```\n\nInvalid links are logged and silently dropped from the rendered navigation.\n\n### Template hardening — `nav.mustache`\n\nAdded `rel=\"noopener noreferrer\"` to all navigation link anchor tags as a\ndefense-in-depth measure:\n\n```html\n<a class=\"nav-link\" href=\"{{link}}\" rel=\"noopener noreferrer\">{{display}}</a>\n```\n\nTests were added to verify that `javascript:` and `ftp://` URIs are rejected\nwhile `http://`, `https://`, and site-relative (`/path`) links are accepted.\n\n## Workarounds\n\nIf upgrading is not immediately possible, audit the navigation configuration\nto ensure all `navItems` link values use only `http://`, `https://`, or\nrelative (`/`) URL schemes.\n\n## References\n\n- [PR #1293 — validate nav links](https://github.com/NationalSecurityAgency/emissary/pull/1293)\n- Original report: GHSA-wjqm-p579-x3ww",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "gov.nsa.emissary:emissary"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "8.39.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 8.38.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/NationalSecurityAgency/emissary/security/advisories/GHSA-cpm7-cfpx-3hvp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-35571"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/NationalSecurityAgency/emissary/pull/1293"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/NationalSecurityAgency/emissary/commit/e2078417464b9004620dde28dcbca2f73ea06c13"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/NationalSecurityAgency/emissary"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-07T20:17:14Z",
    "nvd_published_at" : "2026-04-07T16:16:29Z"
  }
}