Bypass of CSRF protection in the presence of predictable userInfo
Description
The 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.
@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. Whenever userInfo parameter is missing, or its value can be predicted for the target user account, network and same-site 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.
As 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.
Patches
This is patched in version 6.3.0 and v4.1.0.
Workarounds
As a workaround, developers can use a random, non-predictable userInfo parameter for each user.
Credits
- Pedro Adão (@pedromigueladao), Instituto Superior Técnico, University of Lisbon
- Marco Squarcina (@lavish), Security & Privacy Research Unit, TU Wien
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | @fastify/csrf-protection | < 4.1.0, >= 5.0.0, < 6.3.0 | 4.1.0, 6.3.0 |
References
- https://github.com/fastify/csrf-protection/security/advisories/GHSA-qrgf-9gpc-vrxw
- https://github.com/fastify/csrf-protection/security/advisories/GHSA-rc4q-9m69-gqp8
- https://nvd.nist.gov/vuln/detail/CVE-2023-27495
- https://github.com/fastify/csrf-protection/commit/be3e5761f37aa05c7c1ac8ed44499c51ecec8058
- https://github.com/fastify/csrf-protection
- https://github.com/fastify/csrf-protection/releases/tag/v4.1.0
- https://github.com/fastify/csrf-protection/releases/tag/v6.3.0
- https://www.cvedetails.com/cve/CVE-2021-29624
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N- Weakness (CWE)
CWE-352- Platform
- npm
- Package
@fastify/csrf-protection- Disclosed
- 20.04.2023
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-qrgf-9gpc-vrxw - CC BY 4.0
Vulnerability history: @fastify/csrf-protection
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
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