GHSA-V9WW-2J6R-98Q6

Vulnerability from github – Published: 2026-04-16 22:28 – Updated: 2026-04-16 22:28
VLAI?
Summary
@fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option
Details

Impact

@fastify/middie v9.3.1 and earlier does not read the deprecated (but still functional) top-level ignoreDuplicateSlashes option, only reading from routerOptions. This creates a normalization gap: Fastify's router normalizes duplicate slashes but middie does not, allowing middleware bypass via URLs with duplicate leading slashes (e.g., //admin/secret).

This only affects applications using the deprecated top-level configuration style (fastify({ ignoreDuplicateSlashes: true })). Applications using routerOptions: { ignoreDuplicateSlashes: true } are not affected.

This is distinct from GHSA-8p85-9qpw-fwgw (CVE-2026-2880), which was patched in v9.2.0.

Patches

Upgrade to @fastify/middie >= 9.3.2.

Workarounds

Migrate from deprecated top-level ignoreDuplicateSlashes: true to routerOptions: { ignoreDuplicateSlashes: true }.

Severity ?
7.4 (High)
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Show details on source website
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{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 9.3.1"
      },
      "package": {
        "ecosystem": "npm",
        "name": "@fastify/middie"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "9.3.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33804"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-436"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-16T22:28:54Z",
    "nvd_published_at": "2026-04-16T15:17:34Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\n`@fastify/middie` v9.3.1 and earlier does not read the deprecated (but still functional) top-level `ignoreDuplicateSlashes` option, only reading from `routerOptions`. This creates a normalization gap: Fastify\u0027s router normalizes duplicate slashes but middie does not, allowing middleware bypass via URLs with duplicate leading slashes (e.g., `//admin/secret`).\n\nThis only affects applications using the deprecated top-level configuration style (`fastify({ ignoreDuplicateSlashes: true })`). Applications using `routerOptions: { ignoreDuplicateSlashes: true }` are not affected.\n\nThis is distinct from [GHSA-8p85-9qpw-fwgw](https://github.com/fastify/middie/security/advisories/GHSA-8p85-9qpw-fwgw) (CVE-2026-2880), which was patched in v9.2.0.\n\n### Patches\n\nUpgrade to `@fastify/middie` \u003e= 9.3.2.\n\n### Workarounds\n\nMigrate from deprecated top-level `ignoreDuplicateSlashes: true` to `routerOptions: { ignoreDuplicateSlashes: true }`.",
  "id": "GHSA-v9ww-2j6r-98q6",
  "modified": "2026-04-16T22:28:54Z",
  "published": "2026-04-16T22:28:54Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fastify/middie/security/advisories/GHSA-v9ww-2j6r-98q6"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33804"
    },
    {
      "type": "WEB",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/fastify/middie"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "@fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option"
}


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