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CVE-2025-59934: Critical Vulnerability in Formbricks Prior to Version 4.0.1 – Missing JWT Signature Verification

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Overview

The cybersecurity industry has identified a critical vulnerability, CVE-2025-59934, within Formbricks, an open-source alternative to Qualtrics. This vulnerability, which primarily affects versions of Formbricks prior to 4.0.1, involves a missing JSON Web Token (JWT) signature verification. The severity of this issue is underscored by the potential for system compromise and data leakage, putting user privacy and security at high risk. The vulnerability exists in a crucial security layer of Formbricks, making it an issue of paramount importance.

Vulnerability Summary

CVE ID: CVE-2025-59934
Severity: Critical (9.4 CVSS Score)
Attack Vector: Network
Privileges Required: Low
User Interaction: Required
Impact: Potential system compromise or data leakage

Affected Products

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Product | Affected Versions

Formbricks | Versions prior to 4.0.1

How the Exploit Works

The vulnerability stems from a token validation routine that only decodes JWTs (jwt.decode) without verifying their signatures. In this scenario, both the email verification token login path and the password reset server action use the same validator, which does not check the token’s signature, expiration, issuer, or audience. If an attacker gains knowledge of a user’s id, they can generate an arbitrary JWT with an ‘alg: “none”‘ header. This token can then be used to authenticate as the user and reset the user’s password.

Conceptual Example Code

Here is a hypothetical example of how an attacker could exploit this vulnerability:

POST /password/reset HTTP/1.1
Host: formbricks.example.com
Content-Type: application/json
Authorization: Bearer eyJhbGciOiJub25lIiwidHlwIjoiSldUIn0.eyJ1c2VyLmlkIjoiMTIzNDUifQ.
{ "new_password": "new_password_for_victim" }

In this example, the “Authorization” header contains a JWT token with the “none” algorithm specified and a user.id of “12345”. The payload of the POST request is a new password for the user, effectively allowing the attacker to change the user’s password.

Mitigation

The vulnerability has been patched in version 4.0.1 of Formbricks. It is strongly recommended that users upgrade to this version or later. As a temporary mitigation, users could employ a Web Application Firewall (WAF) or an Intrusion Detection System (IDS) to monitor for and block suspicious activities related to this exploit.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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