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Security Advisories: GSA_kwCzR0hTQS1xcmdmLTlncGMtdnJ4d84AAy5b

Bypass of CSRF protection in the presence of predictable userInfo


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.


This is patched in version 6.3.0 and v4.1.0.


As a workaround, developers can use a random, non-predictable userInfo parameter for each user.


Source: GitHub Advisory Database
Origin: Unspecified
Severity: Moderate
Classification: General
Published: 5 months ago
Updated: 5 months ago

CVSS Score: 5.3
CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

Identifiers: GHSA-qrgf-9gpc-vrxw, CVE-2023-27495

Affected Packages

Versions: >= 5.0.0, < 6.3.0, < 4.1.0
Fixed in: 6.3.0, 4.1.0