{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "4.0.0"
              },
              {
                "fixed": "5.12.2"
              },
              {
                "introduced": "0"
              }
            ],
            "source": [
              "AFFECTED_FIELD",
              "DESCRIPTION"
            ]
          },
          "events": [
            {
              "introduced": "e941c24bf51af7184cf658ca138e069e8c166ef8"
            },
            {
              "fixed": "942a2be8704244db778f8db9a0bb4951b8825156"
            }
          ],
          "repo": "https://github.com/fastify/fastify",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-p68q-wchp-6fh7"
  ],
  "database_specific": {
    "cna_assigner": "openjs",
    "cwe_ids": [
      "CWE-288"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/76xxx/CVE-2026-76169.json"
  },
  "details": "fastify versions \u003e= 4.0.0 and before 5.12.2 can route a malformed URL sent under one plugin prefix to the custom not-found handler of a different sibling plugin, and invoke it without the preHandler hook declared for that handler. The internal not-found router for encapsulated handlers dispatches malformed paths through a single shared handler pointer before URL decoding, ignoring the prefix and skipping the selected handler's normal lifecycle. An unauthenticated attacker can therefore reach an authentication-protected private fallback through an unrelated public prefix and read its full response, bypassing the authentication hook and breaking prefix encapsulation. Users should upgrade to fastify 5.12.2 or later.",
  "id": "CVE-2026-76169",
  "modified": "2026-09-10T03:30:58.937843297Z",
  "published": "2026-09-04T09:51:03.556Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/76xxx/CVE-2026-76169.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-76169"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers"
}