CVE-2025-63700: Clerk-js 5.88.0 OAuth Bypass – A Deep Dive and Remediation

Overview

CVE-2025-63700 identifies a security vulnerability in Clerk-js version 5.88.0. This flaw allows attackers to potentially bypass the OAuth authentication flow by manipulating requests during the One-Time Password (OTP) verification stage. This bypass can lead to unauthorized access to user accounts and sensitive data.

Technical Details

The vulnerability resides in the OTP verification process within Clerk-js 5.88.0. An attacker can intercept and modify the request sent to the server during OTP verification. By manipulating specific parameters within this request, the attacker can circumvent the intended authentication checks, effectively bypassing the OAuth flow and gaining unauthorized access as another user. The specific manipulation techniques are detailed in the linked GitHub repository.

Exploitation requires a deep understanding of the Clerk-js OTP verification implementation. An attacker would need to be able to intercept and modify network requests between the client and the Clerk backend during the OTP verification phase.

CVSS Analysis

Currently, a CVSS score has not been assigned to CVE-2025-63700. The severity is marked as N/A. However, given the potential for complete OAuth bypass, a high severity score is anticipated once the details of the vulnerability are fully assessed and a CVSS vector is calculated. We will update this section as soon as official CVSS metrics are available.

Possible Impact

The successful exploitation of CVE-2025-63700 can have severe consequences:

• Account Takeover: Attackers can gain unauthorized access to user accounts, potentially leading to data theft, financial fraud, and other malicious activities.
• Data Breach: If user accounts hold sensitive information, attackers can exfiltrate this data, leading to a data breach and potential legal ramifications for the affected application.
• Reputation Damage: A successful attack can severely damage the reputation of the application using Clerk-js and erode user trust.
• Privilege Escalation: If the compromised account has elevated privileges, the attacker could gain access to sensitive administrative functions.

Mitigation and Patch Steps

The recommended mitigation steps are as follows:

1. Upgrade Clerk-js: The most critical step is to upgrade Clerk-js to a patched version that addresses CVE-2025-63700. Check the Clerk.com website for the latest version and release notes.
2. Implement Server-Side Validation: Ensure robust server-side validation of all OTP verification requests. Do not rely solely on client-side checks. Verify the integrity of the request and confirm that the OTP is valid for the specific user and authentication attempt.
3. Rate Limiting: Implement rate limiting on OTP verification requests to prevent brute-force attacks.
4. Monitor for Suspicious Activity: Monitor application logs for suspicious OTP verification attempts and unusual authentication patterns.
5. Review Authentication Flows: Conduct a thorough review of all authentication flows to identify and address any potential vulnerabilities.