CVE-2025-62236 is a vulnerability classified under CWE-204 (Observable Response Discrepancy) affecting the Frontier Airlines website flyfrontier.com. The issue arises because a publicly accessible endpoint responds differently based on whether an email address is associated with an existing account. This discrepancy allows unauthenticated, remote attackers to enumerate valid email addresses by submitting them to the endpoint and analyzing the responses. The vulnerability does not require any authentication or user interaction, making it easier to exploit at scale. The CVSS v3.1 base score is 5.3 (medium), reflecting that the impact is limited to confidentiality (disclosure of valid email addresses) without affecting integrity or availability. Although no known exploits exist currently, the ability to confirm valid email addresses can facilitate further attacks such as phishing, social engineering, or credential stuffing, especially when combined with leaked password databases. The vulnerability affects all versions of the flyfrontier.com platform, and no patches or mitigations have been officially released as of the publication date. The root cause is the inconsistent response behavior of the email validation endpoint, which leaks information about account existence. Remediation would require standardizing responses to avoid revealing account status and implementing additional protections such as rate limiting and CAPTCHA challenges.

For European organizations, the primary impact is indirect but significant. Employees or customers who use Frontier Airlines services may have their email addresses enumerated by attackers, increasing their risk of targeted phishing or social engineering attacks. This can lead to credential compromise, unauthorized access to corporate resources, or financial fraud. Additionally, if European travel agencies or partners integrate with Frontier Airlines systems or share customer data, they may also be exposed to increased risk. The vulnerability does not directly compromise European IT infrastructure but raises the threat level for identity-based attacks. Organizations with frequent transatlantic travel or business relationships with Frontier Airlines should heighten awareness and monitoring for suspicious emails or login attempts. The exposure of valid email addresses can also facilitate broader reconnaissance campaigns targeting European users, potentially leading to multi-stage attacks.

To mitigate this vulnerability, Frontier Airlines should immediately standardize the email validation endpoint responses so that they do not reveal whether an email address is registered, for example by returning a generic success message regardless of input. Implementing rate limiting and CAPTCHA challenges on the endpoint can reduce automated enumeration attempts. Organizations should monitor logs for unusual spikes in email validation requests and suspicious login attempts. Employees and customers should be educated about phishing risks and encouraged to use multi-factor authentication (MFA) on their accounts. European organizations can also implement email filtering and threat intelligence solutions to detect and block phishing campaigns leveraging enumerated addresses. Collaboration with Frontier Airlines to receive timely updates and patches is essential. Finally, security teams should conduct periodic audits of public-facing endpoints to identify and remediate similar information disclosure issues.