Vulnerabilities in pkg:npm/@simplewebauthn/server

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6hxq-p678-4hr2",
  "modified" : "2026-09-04T17:33:20Z",
  "published" : "2026-09-04T17:33:20Z",
  "aliases" : [ ],
  "summary" : "SimpleWebAuthn: Registration verification does not sufficiently ensure that attestation certificates chain to a trust anchor",
  "details" : "## Summary\n`validateCertificatePath()` does not verify that an attestation's certificate chain actually terminates at a configured trust anchor. When walking the chain it stops at the first self-signed certificate it finds (which could be user-supplied), and exits early.\n\nThis happens before the configured Apple/Google/etc trust anchor (which is concatenated to the end of the chain) is reached.\n\nA user can therefore register a credential and have the server accept it as if it were backed by a genuine Apple / Android SafetyNet / Yubikey / etc.\n\n## Details\n`packages/server/src/helpers/validateCertificatePath.ts`:\n\nThe configured trust anchor is appended to the end of the untrusted chain (line **83**):\n\n```ts\nconst x5cWithTrustAnchor = x5cCertsParsed.concat([anchor]);\n```\n\nThe walk then verifies each cert was signed by the next, but breaks on the first self-signed cert (lines **104–116**):\n\n```ts\nif (issuer.subject === issuer.issuer) {\n  // Root cert detected, make sure it signed itself\n  const issuerSignedIssuer = await issuer.verify(\n    { publicKey: issuer.publicKey, signatureOnly: true },\n    WebCrypto,\n  );\n  if (!issuerSignedIssuer) {\n    throw new InvalidSubjectAndIssuer();\n  }\n  break;   // <-- exits before the appended trust anchor is ever checked if user supplied self-signed cert comes first\n}\n```\n\nThe success condition is therefore \"the certs form an internally-consistent chain ending in some self-signed cert\" Rather than \"the chain terminates at one of the configured trust anchors.\"\n\n## Exploit shape\n\n```\nattacker sends:  x5c = [ forgedLeaf (signed by attacker root),\n                         attackerSelfSignedRoot ]\n\nlibrary builds:  [ forgedLeaf, attackerSelfSignedRoot, <configured Apple/Google/etc root> ]\n\nwalk:  forgedLeaf -> attackerSelfSignedRoot        (verifies, attacker controls both)\n       attackerSelfSignedRoot is self-signed        -> break\n       attackerSelfSignedRoot -> configured root    (NEVER CHECKED)\n```\n\n`return true`. The configured anchor never gets checked.\n\n\nAs far as observed, all attestation enforcement uses validateCertificatePath when using MDS etc.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@simplewebauthn/server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "13.3.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 13.3.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/MasterKale/SimpleWebAuthn/security/advisories/GHSA-6hxq-p678-4hr2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/MasterKale/SimpleWebAuthn/commit/67a41fed3dfd96cab1dcf414f6d1792a72e06e35"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/MasterKale/SimpleWebAuthn/commit/8a53d70f42bcbb7c744ef1b90e6db35bc4b26d06"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/MasterKale/SimpleWebAuthn/commit/dd0d73c716a528e6645efafbd43a972b64df71f9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/MasterKale/SimpleWebAuthn"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/MasterKale/SimpleWebAuthn/releases/tag/v13.3.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-295", "CWE-296" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-04T17:33:20Z",
    "nvd_published_at" : null
  }
}