CVE-2026-2880: @fastify/middie @fastify/middie Has Improper Path Normalization Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-8p85-9qpw-fwgw",
  "modified" : "2026-02-28T02:47:17Z",
  "published" : "2026-02-28T02:47:17Z",
  "aliases" : [ "CVE-2026-2880" ],
  "summary" : "@fastify/middie has Improper Path Normalization when Using Path-Scoped Middleware",
  "details" : "## Summary\nA path normalization inconsistency in `@fastify/middie` can result in authentication/authorization bypass when using path-scoped middleware (for example, `app.use('/secret', auth)`).\n\nWhen Fastify router normalization options are enabled (such as `ignoreDuplicateSlashes`, `useSemicolonDelimiter`, and related trailing-slash behavior), crafted request paths may bypass middleware checks while still being routed to protected handlers.\n\n## Impact\nAn unauthenticated remote attacker can access endpoints intended to be protected by middleware-based auth/authorization controls by sending specially crafted URL paths (for example, `//secret` or `/secret;foo=bar`), depending on router option configuration.\n\nThis may lead to unauthorized access to protected functionality and data exposure.\n\n## Affected versions\n- Confirmed affected: `@fastify/middie@9.1.0`\n- All versions prior to the patch are affected.\n\n## Patched versions\n- Fixed in: *9.2.0*\n\n## Details\nThe issue is caused by canonicalization drift between:\n1. `@fastify/middie` path matching for `app.use('/prefix', ...)`, and\n2. Fastify/find-my-way route lookup normalization.\n\nBecause middleware and router did not always evaluate the same normalized path, auth middleware could be skipped while route resolution still succeeded.\n\n## Workarounds\nUntil patched version is deployed:\n- Avoid relying solely on path-scoped middie guards for auth/authorization.\n- Enforce auth at route-level handlers/hooks after router normalization.\n- Disable risky normalization combinations only if operationally feasible.\n\n## Resources\n- Fluid Attacks Disclosure Policy: https://fluidattacks.com/advisories/policy\n- Fluid Attacks advisory URL: https://fluidattacks.com/advisories/jimenez\n\n## Credits\n- **Cristian Vargas** (Fluid Attacks Research Team) — discovery and report.\n- **Oscar Uribe** (Fluid Attacks) — coordination and disclosure.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@fastify/middie"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "9.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fastify/middie/security/advisories/GHSA-8p85-9qpw-fwgw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-2880"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/middie/commit/140e0dd0359d890fec7e6ea1dcc5134d6bd554d4"
  }, {
    "type" : "WEB",
    "url" : "https://fluidattacks.com/advisories/jimenez"
  }, {
    "type" : "WEB",
    "url" : "https://fluidattacks.com/advisories/policy"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fastify/middie"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/middie/releases/tag/v9.2.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-28T02:47:17Z",
    "nvd_published_at" : "2026-02-27T19:16:12Z"
  }
}