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Insecure CORS Configuration Allowing Wildcard Origin with Credentials

Critical
ReneWerner87 published GHSA-fmg4-x8pw-hjhg Feb 21, 2024

Package

gomod github.com/gofiber/fiber/v2 (Go)

Affected versions

< 2.52.1

Patched versions

>= 2.52.1
gomod github.com/gofiber/fiber/v2/middleware/cors (Go)
< 2.52.1
>= 2.52.1

Description

The CORS middleware allows for insecure configurations that could potentially expose the application to multiple CORS-related vulnerabilities. Specifically, it allows setting the Access-Control-Allow-Origin header to a wildcard ("*") while also having the Access-Control-Allow-Credentials set to true, which goes against recommended security best practices.

Impact

The impact of this misconfiguration is high as it can lead to unauthorized access to sensitive user data and expose the system to various types of attacks listed in the PortSwigger article linked in the references.

Proof of Concept

The code in cors.go allows setting a wildcard in the AllowOrigins while having AllowCredentials set to true, which could lead to various vulnerabilities.

Potential Solution

Here is a potential solution to ensure the CORS configuration is secure:

func New(config ...Config) fiber.Handler {
    if cfg.AllowCredentials && cfg.AllowOrigins == "*" {
        panic("[CORS] Insecure setup, 'AllowCredentials' is set to true, and 'AllowOrigins' is set to a wildcard.")
    }
    // Return new handler goes below
}

The middleware will not allow insecure configurations when using `AllowCredentials` and `AllowOrigins`.

Workarounds

For the meantime, users are advised to manually validate the CORS configurations in their implementation to ensure that they do not allow a wildcard origin when credentials are enabled. The browser fetch api, browsers and utilities that enforce CORS policies are not affected by this.

References

MDN Web Docs on CORS Errors
CodeQL on CORS Misconfiguration
PortSwigger on Exploiting CORS Misconfigurations
WhatWG CORS protocol and credentials

Severity

Critical

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
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
Low

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:L/PR:N/UI:N/S:U/C:H/I:H/A:L

CVE ID

CVE-2024-25124

Credits