{"id":"CVE-2026-2880","aliases":["GHSA-8p85-9qpw-fwgw"],"url":"https://o3.security/vulnerability/CVE-2026-2880","summary":"@fastify/middie has an improper path normalization vulnerability","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.","published":"2026-02-27T18:25:37.428Z","modified":"2026-10-28T02:31:08.049961552Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@fastify/middie","fixedVersion":"9.2.0"}],"fix":{"url":"https://github.com/fastify/middie/commit/140e0dd0359d890fec7e6ea1dcc5134d6bd554d4","label":"fastify/middie@140e0dd"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/2xxx/CVE-2026-2880.json"},{"type":"ADVISORY","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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:31:08.049961552Z"}}