EUVD-2025-201128

Comprehensive Technical Analysis of EUVD-2025-201128

1. Vulnerability Assessment and Severity Evaluation

The vulnerability described in EUVD-2025-201128 affects Cal.com, an open-source scheduling software. The flaw in the login credentials provider allows an attacker to bypass password verification when a TOTP (Time-based One-Time Password) code is provided. This vulnerability is rated with a CVSS (Common Vulnerability Scoring System) base score of 9.9, indicating a critical severity level.

CVSS Vector Breakdown:

• AV:N (Network Vector): The vulnerability is exploitable over the network.
• AC:L (Low Complexity): The attack requires low skill or resources to exploit.
• AT:N (No Authentication): No authentication is required to exploit the vulnerability.
• PR:N (No Privileges Required): No privileges are required to exploit the vulnerability.
• UI:N (No User Interaction): No user interaction is required to exploit the vulnerability.
• VC:H (High Confidentiality Impact): The vulnerability has a high impact on confidentiality.
• VI:H (High Integrity Impact): The vulnerability has a high impact on integrity.
• VA:H (High Availability Impact): The vulnerability has a high impact on availability.
• SC:H (High Scope Change): The vulnerability affects components beyond its security scope.
• SI:H (High Scope Integrity): The vulnerability affects the integrity of components beyond its security scope.
• SA:N (No Scope Availability): The vulnerability does not affect the availability of components beyond its security scope.

2. Potential Attack Vectors and Exploitation Methods

The primary attack vector involves exploiting the flaw in the login credentials provider. An attacker could:

• Intercept TOTP Codes: Obtain a valid TOTP code through phishing, social engineering, or other means.
• Bypass Password Verification: Use the TOTP code to bypass the password verification process, gaining unauthorized access to user accounts.

3. Affected Systems and Software Versions

The vulnerability affects all versions of Cal.com prior to 5.9.8. Users and organizations running any version of Cal.com below 5.9.8 are at risk.

4. Recommended Mitigation Strategies

Immediate Actions:

• Update Software: Upgrade to Cal.com version 5.9.8 or later, which includes the fix for this vulnerability.
• Monitor Logs: Closely monitor authentication logs for any suspicious activity or unauthorized access attempts.

Long-Term Strategies:

• Implement Multi-Factor Authentication (MFA): Ensure that MFA is properly configured and enforced.
• Regular Security Audits: Conduct regular security audits and vulnerability assessments to identify and mitigate similar issues.
• User Education: Educate users about the risks of phishing and social engineering attacks, and how to protect their TOTP codes.

5. Impact on European Cybersecurity Landscape

The vulnerability poses a significant risk to European organizations using Cal.com for scheduling purposes. Unauthorized access to user accounts can lead to data breaches, loss of sensitive information, and potential disruption of services. Given the critical nature of the vulnerability, it is essential for organizations to prioritize patching and implementing robust security measures to protect against such threats.

6. Technical Details for Security Professionals

Conditional Logic Flaw: The root cause of the vulnerability is a problematic conditional logic in the authentication flow. Specifically, the flaw allows the TOTP code to bypass the password verification step, granting access to the account without verifying the password.

Code Review: Security professionals should conduct a thorough code review of the authentication mechanisms in Cal.com to ensure that similar flaws do not exist elsewhere. Particular attention should be paid to the logic handling TOTP codes and password verification.

Incident Response: In case of a suspected breach, incident response teams should:

• Isolate Affected Systems: Immediately isolate any systems suspected of being compromised.
• Forensic Analysis: Perform a detailed forensic analysis to determine the extent of the breach and identify any compromised data.
• Notify Stakeholders: Inform relevant stakeholders, including users and regulatory bodies, about the incident and the steps being taken to mitigate it.

References: For further details, refer to the GitHub security advisory: GHSA-9r3w-4j8q-pw98.

By addressing this vulnerability promptly and implementing robust security measures, organizations can significantly reduce the risk of unauthorized access and data breaches.