{"id":"CVE-2021-21321","aliases":["GHSA-qmw8-3v4g-gwj4"],"url":"https://o3.security/vulnerability/CVE-2021-21321","summary":"Prefix escape","details":"### Impact\n\nBy crafting a specific URL, it is possible to escape the prefix of the proxied backend service.\nIf the base url of the proxied server is `/pub/`, a user expect that accessing `/priv` on the target service would not be possible. Unfortunately, it is.\n\n[CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N](https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N)\n\n### Patches\n\nA patch have been submitted by Corey Farrell git@cfware.com, the reporter.\nAll releases after v4.0.2 include the fix.\n\n### Workarounds\n\nThere are no workaround available.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [fastify-reply-from](https://github.com/fastify/fastify-reply-from)\n* Email us at [hello@matteocollina.com](mailto:hello@matteocollina.com)","published":"2021-03-02T04:15:12.487Z","modified":"2026-08-07T17:28:12.862976Z","cvss":{"score":10,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"fastify-reply-from","fixedVersion":"4.0.2"}],"fix":{"url":"https://github.com/fastify/fastify-reply-from/commit/dea227dda606900cc01870d08541b4dcc69d3889","label":"fastify/fastify-reply-from@dea227d"},"references":[{"type":"ADVISORY","url":"https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-qmw8-3v4g-gwj4"},{"type":"ADVISORY","url":"https://www.npmjs.com/package/fastify-reply-from"},{"type":"FIX","url":"https://github.com/fastify/fastify-reply-from/commit/dea227dda606900cc01870d08541b4dcc69d3889"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21321"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T17:28:12.862976Z"}}