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Bypass of CSRF protection in the presence of predictable userInfo

Moderate
mcollina published GHSA-qrgf-9gpc-vrxw Apr 20, 2023

Package

npm @fastify/csrf-protection (npm)

Affected versions

<= 4.0.1 && 5.0.0 <= 6.2.0

Patched versions

>= 4.1.0 < 5.0.0 && >= 6.3.0

Description

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

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

CVE ID

CVE-2023-27495

Weaknesses

Cross-Site Request Forgery (CSRF)

The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request. Learn more on MITRE.

Credits