{"id":"GHSA-v9ww-2j6r-98q6","summary":"@fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes option","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's 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 }`.","aliases":["CVE-2026-33804"],"modified":"2026-04-16T22:57:17.885Z","published":"2026-04-16T22:28:54Z","database_specific":{"cwe_ids":["CWE-436"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-04-16T22:28:54Z","nvd_published_at":"2026-04-16T15:17:34Z"},"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"}],"affected":[{"package":{"name":"@fastify/middie","ecosystem":"npm","purl":"pkg:npm/%40fastify/middie"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"9.3.2"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 9.3.1","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-v9ww-2j6r-98q6/GHSA-v9ww-2j6r-98q6.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"}]}