{"id":"CVE-2026-35571","aliases":["GHSA-cpm7-cfpx-3hvp"],"url":"https://o3.security/vulnerability/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","published":"2026-04-07T15:26:30.391Z","modified":"2026-10-28T02:31:13.539660831Z","cvss":{"score":4.8,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Maven","name":"gov.nsa.emissary:emissary","fixedVersion":"8.39.0"}],"fix":{"url":"https://github.com/NationalSecurityAgency/emissary/pull/1293","label":"NationalSecurityAgency/emissary#1293"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/35xxx/CVE-2026-35571.json"},{"type":"ADVISORY","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":"FIX","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"},{"type":"WEB","url":"https://github.com/NationalSecurityAgency/emissary/releases/tag/8.39.0"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:31:13.539660831Z"}}