CVE-2026-35583: Emissary Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hxf2-gm22-7vcm",
  "modified" : "2026-04-08T00:12:55Z",
  "published" : "2026-04-08T00:12:55Z",
  "aliases" : [ "CVE-2026-35583" ],
  "summary" : "Emissary has a Path Traversal via Blacklist Bypass in Configuration API",
  "details" : "## Summary\n\nThe configuration API endpoint (`/api/configuration/{name}`) validated\nconfiguration names using a blacklist approach that checked for `\\`, `/`, `..`,\nand trailing `.`. This could potentially be bypassed using URL-encoded variants,\ndouble-encoding, or Unicode normalization to achieve path traversal and read\nconfiguration files outside the intended directory.\n\n## Details\n\n### Vulnerable code — `Configs.java` (line 126)\n\n```java\nprotected static String validate(String config) {\n    if (StringUtils.isBlank(config) || config.contains(\"\\\\\") || config.contains(\"/\")\n        || config.contains(\"..\") || config.endsWith(\".\")) {\n        throw new IllegalArgumentException(\"Invalid config name: \" + config);\n    }\n    return Strings.CS.appendIfMissing(config.trim(), CONFIG_FILE_ENDING);\n}\n```\n\n### Weakness\n\nThe blacklist blocked literal `\\`, `/`, `..`, and trailing `.` but could\npotentially miss:\n\n- URL-encoded variants (`%2e%2e%2f`) if decoded after validation\n- Double-encoded sequences (`%252e%252e%252f`)\n- Unicode normalization bypasses\n- The approach relies on string matching rather than canonical path resolution\n\n### Impact\n\n- Potential read access to configuration files outside the intended config\n  directory\n- Information disclosure of sensitive configuration values\n\n## Remediation\n\nFixed in [PR #1292](https://github.com/NationalSecurityAgency/emissary/pull/1292),\nmerged into release 8.39.0.\n\nThe blacklist was replaced with an allowlist regex that only permits characters\nmatching `^[a-zA-Z0-9._-]+$`:\n\n```java\nprotected static final Pattern VALID_CONFIG_NAME = Pattern.compile(\"^[a-zA-Z0-9._-]+$\");\n\nprotected static String validate(String config) {\n    if (!VALID_CONFIG_NAME.matcher(config).matches() || config.contains(\"..\") || config.endsWith(\".\")) {\n        throw new IllegalArgumentException(\"Invalid config name: \" + config);\n    }\n    return Strings.CS.appendIfMissing(config.trim(), CONFIG_FILE_ENDING);\n}\n```\n\nThis ensures that any character outside the allowed set — including encoded\nslashes, percent signs, and Unicode sequences — is rejected before the config\nname reaches the filesystem.\n\nTests were added to verify that URL-encoded (`%2e%2e%2f`), double-encoded\n(`%252e%252e%252f`), and Unicode (`U+002F`) traversal attempts are blocked.\n\n## Workarounds\n\nIf upgrading is not immediately possible, deploy a reverse proxy or WAF rule\nthat rejects requests to `/api/configuration/` containing encoded path traversal\nsequences.\n\n## References\n\n- [PR #1292 — validate config name with an allowlist](https://github.com/NationalSecurityAgency/emissary/pull/1292)\n- Original report: GHSA-wjqm-p579-x3ww",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "gov.nsa.emissary:emissary"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "8.39.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/NationalSecurityAgency/emissary/security/advisories/GHSA-hxf2-gm22-7vcm"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-35583"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/NationalSecurityAgency/emissary/pull/1292"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/NationalSecurityAgency/emissary"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-08T00:12:55Z",
    "nvd_published_at" : "2026-04-07T17:16:33Z"
  }
}