{"id":"CVE-2023-27495","aliases":["GHSA-qrgf-9gpc-vrxw"],"url":"https://o3.security/vulnerability/CVE-2023-27495","summary":"Bypass of CSRF protection in the presence of predictable userInfo in @fastify/csrf-protection","details":"## Description\nThe [CSRF](https://owasp.org/www-community/attacks/csrf) protection enforced by the `@fastify/csrf-protection` library in combination with `@fastify/cookie` can be bypassed from network and same-site attackers under certain conditions.\n\n`@fastify/csrf-protection` supports an optional `userInfo` parameter that binds the CSRF token to the user. This parameter has been introduced to prevent cookie-tossing attacks as a fix for [CVE-2021-29624](https://www.cvedetails.com/cve/CVE-2021-29624). Whenever `userInfo` parameter is missing, or its value can be predicted for the target user account, network and [same-site](https://canitakeyoursubdomain.name/) attackers can 1. fixate a `_csrf` cookie in the victim's browser, and 2. forge CSRF tokens that are valid for the victim's session. This allows attackers to bypass the CSRF protection mechanism.\n\nAs a fix, `@fastify/csrf-protection` starting from version 6.3.0 (and v4.1.0) includes a server-defined secret `hmacKey` that cryptographically binds the CSRF token to the value of the `_csrf` cookie and the `userInfo` parameter, making tokens non-spoofable by attackers. This protection is effective as long as the `userInfo` parameter is unique for each user.\n\n### Patches\n\nThis is patched in version 6.3.0 and v4.1.0.\n\n### Workarounds\n\nAs a workaround, developers can use a random, non-predictable `userInfo` parameter for each user.\n\n## Credits\n* Pedro Adão (@pedromigueladao), [Instituto Superior Técnico, University of Lisbon](https://tecnico.ulisboa.pt/)\n* Marco Squarcina (@lavish), [Security & Privacy Research Unit, TU Wien](https://secpriv.wien/)","published":"2023-04-20T17:05:21.515Z","modified":"2026-10-28T02:30:49.323498028Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@fastify/csrf-protection","fixedVersion":"4.1.0"},{"ecosystem":"npm","name":"@fastify/csrf-protection","fixedVersion":"6.3.0"}],"fix":{"url":"https://github.com/fastify/csrf-protection/commit/be3e5761f37aa05c7c1ac8ed44499c51ecec8058","label":"fastify/csrf-protection@be3e576"},"references":[{"type":"WEB","url":"https://www.cvedetails.com/cve/CVE-2021-29624"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/27xxx/CVE-2023-27495.json"},{"type":"ADVISORY","url":"https://github.com/fastify/csrf-protection/security/advisories/GHSA-qrgf-9gpc-vrxw"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2023-27495"},{"type":"FIX","url":"https://github.com/fastify/csrf-protection/commit/be3e5761f37aa05c7c1ac8ed44499c51ecec8058"},{"type":"WEB","url":"https://github.com/fastify/csrf-protection/security/advisories/GHSA-rc4q-9m69-gqp8"},{"type":"PACKAGE","url":"https://github.com/fastify/csrf-protection"},{"type":"WEB","url":"https://github.com/fastify/csrf-protection/releases/tag/v4.1.0"},{"type":"WEB","url":"https://github.com/fastify/csrf-protection/releases/tag/v6.3.0"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:49.323498028Z"}}